THE ENGINE OIL BIBLE
How much do you value the engine in your car? The life of your engine depends in no small part on the quality of the oil you put in it - oil is its lifeblood. People typically don't pay much attention to their oil - oil is oil, right? In the bad old days, maybe, but engine oil underwent something of a revolution in the 80's and 90's when hot hatches, 16-valve engines and turbos started to become popular. High compression engines and black death meant the days of one oil catering for everyone were over. Take Castrol for example. They led the field for years with their GTX mineral oil. This was eventually surpassed by semi-synthetic and fully synthetic oils, including GTX2 and GTX3 Lightec. Those were surpassed by Formula SLX and most recently, Castrol GTX Magnatec. All manufacturers have a similar broad spectrum of oils now. I just mention Castrol in particular as they're my oil of choice.
WHAT DOES MY OIL ACTUALLY DO? Your engine oil performs many functions. It stops all the metal surfaces in your engine from grinding together and tearing themselves apart from friction, and it transfers heat away from the combustion cycle. Engine oil must also be able to hold in suspension all the nasty by-products of combustion like silica (silicon oxide) and acids. Finally, engine oil minimises the exposure to oxygen and thus oxidation at higher temperatures. It does all of these things under tremendous heat and pressure. HOW DO I READ THE '5W40' TYPE NUMBER? As oils heat up, they generally get thinner. Single grade oils get too thin when hot for most modern engines which is where multigrade oil comes in. The idea is simple - use science and physics to prevent the base oil from getting too thin when it gets hot. The number before the 'W' is the 'cold' viscosity rating of the oil, and the number after the 'W' is the 'hot' viscosity rating. So a 5W40 oil is one that behaves like a 5-rated single grade oil when cold, but doesn't thin any more than a 40-rated single grade oil when hot. The lower the 'winter' number (hence the 'W'), the easier the engine will turn over when starting in cold climates. There's more detail on this later in the page under both viscosity, and SAE ratings. A QUICK GUIDE TO THE DIFFERENT GRADES OF OIL. Fully Synthetic Characteristics Fuel economy savings Enhances engine performance and power Ensures engine is protected from wear and deposit build-up 0W-30 Ensures good cold starting and quick circulation in freezing 0W-40 temperatures 5W-40 Gets to moving parts of the engine quickly Semi-synthetic Characteristics Better protection 5W-30 Good protection within the first 10 minutes after starting out 10W-40 Roughly three times better at reducing engine wear 15W-40 Increased oil change intervals - don't need to change it quite so often Mineral Characteristics 10W-40 Basic protection for a variety of engines 15W-40 Oil needs to be changed more often WHAT THE HECK WAS 'BLACK DEATH'? Black Death first appeared in the early 80's when a sticky black substance was found to be the cause of many engine seizures in Europe. It was extremely frustrating for vehicle owners because dealers and mechanics had no idea what was going on. Black Death just wasn't covered under insurance - if your engine had it, you paid to fix it yourself. Many engines were affected but Ford and Vauxhall (GM) suffered the most. Faster roads, higher under-hood temperatures, tighter engineering tolerances and overworked engine oils turned out to be contributors to the problem. The oils just couldn't handle it and changed their chemical makeup under pressure into a sort of tar-like glue. This blocked all the oil channels in the engines, starved them of lubrication and caused them to seize. I don't recommend this but you can reproduce the effect with a frying pan, cooking oil and a blowtorch. The cooking oil will heat up far quicker than it's designed to and will turn to a sticky black tar in your pan. Either that or it will set fire to your kitchen, which is why I said "don't do this". Anyway, burning kitchens aside, Black Death was the catalyst for the production of newer higher quality oils, many of them man-made rather than mineral-based. BLACK DEATH FOR THE 21ST CENTURY: SLUDGE There's a snappy new moniker for Black Death now: sludge. The cause is the same as Black Death and it seems to be regardless of maintenance or mileage. The chemical compounds in engine oils break down over time due to prolonged exposure to high temperatures and poor maintenance habits. When the oil oxidises, the additives separate from it and begin to chemically break down and solidify, leading to the baked- on oil deposits turning gelatinous, like black yoghurt. What doesn't help is that due to packaging, modern engines have smaller sumps than their older counterparts, and so hold less oil. This lower volume of oil can't hold as much crap (for want of a better word) and that can lead to earlier chemical breakdown. The most common factor in sludge buildup is a combination of mineral oils, a lack of maintenance by the car owner and harsh driving conditions. However, a 2005 Consumer Reports article discovered that some engines from Audi, Chrysler, Saab, Toyota, and Volkswagen appear prone to sludge almost no matter how often the oil is changed. WHAT DOES SLUDGE LOOK LIKE?
I was contacted by a BMW driver who had been having a particularly harsh time with sludge and was discussing it on the Bimmerfest forums. He posted some images of his problem and other readers posted similarly-framed images of the same engine components in "normal" condition. Here are two of those photos. On the left is what the cam case should look like in a well maintained engine when photographed through the oil filler cap. On the right is what the same type of engine looks like when suffering sludge buildup. In this example, the consensus was that the sludge buildup was caused by an overheating engine, oil that hadn't been changed for 20,000 miles of stop-go city driving, a lot of cold starts and a period of about 12 months in storage without an oil change. Picture credit: Ketchup at the Bimmerfest forums CURING SLUDGE There are no hard and fast rules for curing an engine of sludge buildup. If it's really bad, flushing the engine might be the only cure, but that could also cause even more problems. If flushing the engine results in bits of sludge getting lodged where they can do more damage, you're actually worse off. It's interesting to note that some race techs have reported sludge buildup in race engines as a result of aftermarket additives being used in conjunction with the regular oil. The chemical composition of the additives isn't as neutral as some companies would lead us to believe, and combined with particular types of oil and high-stress driving, they can cause oil breakdown and sludge to appear. The lesson from them appears to be "don't use additives". WHEN IS SLUDGE NOT SLUDGE? Easy; when it's an oil and water emulsion from a leaking or blown head gasket. If this happens, you get a whitish cream coloured sludge on the inside of the oil filler cap that looks like vanilla yoghurt or mayonnaise. The cap is typically cooler than the rest of the cam case and so the oil/water mix tends to condense there. If the underside of your filler cap has this sort of deposit on it, chances are the engine has a blown head gasket. A surefire way to confirm this is if your oil level is going up and your coolant level is going down. The coolant gets through the breaks in the head gasket and mixes with the oil. When it gets to the sump it separates out and the oil floats on top. A more accurate way to check for this condition is to use a combustion leak tester, or block tester. If you're in America, NAPA sell them for about $45 (part #BK 7001006). If you're in England, Sealey sell them for about £70 (model number VS0061). Combustion leak testers are basically a turkey baster filled with PH liquid, with a non-return valve at the bottom. To use one, run your engine for a few minutes until its warm (not hot) then turn it off. Use a protective glove (like an oven glove) and take the radiator or reservoir cap off. Plug the bottom of the combustion leak tester into the hole and squeeze the rubber bulb on top. It will suck air from the top of the coolant through the non-return valve and bubble it through the PH liquid. If the liquid changes colour (normally blue to yellow), it means there is combustion gas in the coolant which means a head gasket leak. Note: There is one other possible cause for the mayonnaise: a blocked scavenger hose. Most engines have a hose that comes off the cam cover and returns to the engine block somewhere via a vacuum line. This is the scavenger hose that scavenges oil vapour and gasses that build up in the cam cover. If it's blocked you can end up with a buildup of condensation inside the cam cover, which can manifest itself as the yellow goop inside the filler cap. VW / AUDI SLUDGE PROBLEMS While the the 1.8T engines in Audi A4's, Audi TT, VW Passat, Jetta, Golf, New Bettle, are all very prone to sludge build-up, Audi/VW does not have an extended warranty for them from the factory. The factory warranty is 4 year/50,000 miles but it can be extended if purchased. Although Audi/VW now has 10,000 mile service intervals, oil changes can be done between "services", and should be done if the vehicle is driven in heavy traffic, offroad, and non-highway use. Also, Audi/ VW will only warrant an engine if the customer has proof of all their oil changes. As of 2004 I belive all 1.8T engines must use synthetic oil. So if you own one of these sludge-prone engines, what can you do? Obviously, Volkswagen Audi Group (VAG) states that you use only VW/Audi recommended oil. You should also keep up on your oil changes, making them more frequent if you drive hard or haul a lot of cargo. The most important thing for the VW or Audi owner is this: if the oil light comes on and beeps the high pitch beep that almost everyone ignores, pull over and shut the engine down immediately. Many VAG engines can be saved by this procedure. Have the vehicled towed to a VAG dealer. Their standard procedure is to inspect the cam bearings; if they're not scored, the oil pan will be removed and cleaned out and all the crankcase breather hoses and the oil pickup tube will be replaced. They'll do an oil pressure test with a mechanical gauge, and hopefully will also replace the turbo lines. Finally, the turbo will be checked for bearing free-play. The VAG turbos run really hot even with proper oil and coolant supply - that's why you need a good quality synthetic in them. TOYOTA SLUDGE PROBLEMS For their part, Toyota have the dubious honour of having the most complaints about sludge buildup in their engines - over 5,000 in 2008 alone. At the time of writing there is a class action suit going on against them. Details can be found at www.oilgelsettlement.com SAAB SLUDGE PROBLEMS For an example of sludge in a Saab 9 5 Aero with only 42,000 miles on it, you might be interested to read my case study on this engine, put together with the help of a reader. Our sludge case study. Like the site? The page you're reading is free, but if you like what you see and feel you've learned something, a small donation to help pay down my car loan would be appreciated. Thank you.
MINERAL OR SYNTHETIC MOTOR OIL? Mineral oils are based on oil that comes from dear old Mother Earth which has been refined. Synthetic oils are mostly concocted by chemists wearing white lab coats in oil company laboratories. The only other type is semi-synthetic, sometimes called premium, which is a blend of the two. It is safe to mix the different types, but it's wiser to switch completely to a new type rather than mixing. SYNTHETICS Despite their name, most synthetic derived motor oils (ie Mobil 1, Castrol Formula RS etc) are actually derived from mineral oils - they are mostly Polyalphaolifins and these come from the purest part of the mineral oil refraction process, the gas. PAO oils will mix with normal mineral oils which means you can add synthetic to mineral, or mineral to synthetic without your engine seizing up (although I've heard Mobil 1 is actually made by reformulating ethanol). These bases are pretty stable, and by stable I mean 'less likely to react adversely with other compounds' because they tend not to contain reactive carbon atoms. Reactive carbon has a tendency to combine with oxygen creating an acid. (As you can imagine, in an oil this would be A Bad Thing.) They also have high viscosity indices and high temperature oxidative stability. Typically a small amount of diester synthetic (a compound containing two ester groups) is added to counteract seal swell too. These diesters act as a detergent and will attack carbon residuals. So think of synthetic oils as custom-built oils. They're designed to do the job efficiently but without any of the excess baggage that can accompany mineral based oils. PURE SYNTHETICS Pure synthetic oils (polyalkyleneglycol) are the types used almost exclusively within the industrial sector in polyglycol oils for heavily loaded gearboxes. These are typically concocted by even more intelligent blokes in even whiter lab coats. These chaps break apart the molecules that make up a variety of substances, like vegetable and animal oils, and then recombine the individual atoms that make up those molecules to build new, synthetic molecules. This process allows the chemists to actually "fine tune" the molecules as they build them. Clever stuff. But Polyglycols don't mix with normal mineral oils.
While we're on synthetic oils, I should mention Amsoil. They contacted me and asked to point out the following: Amsoil do NOT produce or market oil additives and do not wish to be associated with oil additives. They are a formulator of synthetic lubricants for automotive and industrial applications and have been in business for 30+ years. They are not a half-hour infomercial or fly-by-night product, nor have they ever been involved in a legal suit regarding their product claims in that 30+ year span. Many Amsoil products are API certified, and ALL of our products meet and in most cases exceed the specifications of ILSAC, AGMA etc. Their lubricants also exceed manufacturers specifications and Amsoil are on many manufacturers approval lists. They base their claims on ASTM certified tests and are very open to anyone, with nothing to hide.
Amsoil recommend engine oil additives are NOT to be used with their products. They have a pretty good FAQ on the Amsoil website: Amsoil FAQ (external link). There is also a particularly good page talking about testing Amsoil in taxis. IF I PUT NEW, FULLY SYNTHETIC OIL IN MY OLDER ENGINE, WILL THE SEALS LEAK? This question comes up a lot from people who've just bought a used vehicle and are wanting to start their history with the car on fresh oil. The short answer: generally speaking, not any more. The caveat is that your engine must be in good working order and not be leaking right now. If that's the case, most modern oils are fully compatible with the elastomeric materials that engine seals are made from, and you shouldn't have any issues with leaks. The longer answer: MIXING MINERAL AND SYNTHETIC OILS Here's the current thinking on the subject of mixing mineral and synthetic oils. This information is based on the answer to a technical question posed on the Shell Oil website: There is no scientific data to support the idea that mixing mineral and synthetic oils will damage your engine. When switching from a mineral oil to a synthetic, or vice versa, you will potentially leave a small amount of residual oil in the engine. That's perfectly okay because synthetic oil and mineral-based motor oil are, for the most part, compatible with each other. (The exception is pure synthetics. Polyglycols don't mix with normal mineral oils.) There is also no problem with switching back and forth between synthetic and mineral based oils. In fact, people who are "in the know" and who operate engines in areas where temperature fluctuations can be especially extreme, switch from mineral oil to synthetic oil for the colder months. They then switch back to mineral oil during the warmer months. There was a time, years ago, when switching between synthetic oils and mineral oils was not recommended if you had used one product or the other for a long period of time. People experienced problems with seals leaking and high oil consumption but changes in additive chemistry and seal material have taken care of those issues. And that's an important caveat. New seal technology is great, but if you're still driving around in a car from the 80's with its original seals, then this argument becomes a bit of a moot point - your seals are still going to be subject to the old leakage problems no matter what newfangled additives the oil companies are putting in their products. FLUSHING OILS These are special compound oils that are very, very thin. They almost have the consistency of tap water both when cold and hot. Typically they are 0W/20 oils. Their purpose is for cleaning out all the gunk which builds up inside an engine. Note: Some hybrid vehicles now require 0W20, so if you're a hybrid driver, check your owner's manual. Also I believe Honda switched to recommending 0W20 in 2011 to meet their CAFE ratings (thinner oil gives less drag on engine parts which improves - fractionally - the mpg). If you look at 2010 models vs 2011, you'll see things like the Element and CR- V getting a tiny mpg boost in the official figures despite being the exact same car. They achieved this by remapping the gearbox shift points and dropping the cold viscosity rating on the oil. In reality unless you live in northern Alaska, or do an above average number of cold-start short journeys, 5W20 ought to be more than suitable. DO I NEED A FLUSHING OIL? Unless there's something seriously wrong with your engine, like you've filled it with milk or shampoo, you really ought never to need a flushing oil. If you do decide to do an oil flush, there's two ways of doing it. You can either use a dedicated flushing oil, or a flushing additive in your existing oil. Either way it's wise to change the filter first so you have a clean one to collect all the gunk. (This typically means draining the oil or working fast). Once you have a new filter in place, and the flushing oil (or flushing solution) in there, run the engine at a fast idle for about 20 minutes. Finally, drain all this off (and marvel at the crap that comes out with it), replace the oil filter again, refill with a good synthetic oil and voila! Clean(er) engine. For the curious amongst you, looking in the oil filter that was attached when you did the flush will be an educational exercise in the sort of debris that used to be in your engine. Of course, like most things nowadays, there's a condition attached when using flushing oils. In an old engine you really don't want to remove all the deposits. Some of these deposits help seal rings, lifters and even some of the flanges between the heads, covers, pan and the block, where the gaskets are thin. I have heard of engines with over 280,000km that worked fine, but when flushed, failed in a month because the blow-by past the scraper ring (now really clean) contaminated the oil and ruined the rod bearings. USING DIESEL OIL FOR FLUSHING A question came up some time ago about using diesel-rated oils to flush out petrol engines. The idea was that because of the higher detergent levels in diesel engine oil, it might be a good cleaner / flusher for a non-diesel engine. Well most of the diesel oil specification oils can be used in old petrol engines for cleaning, but you want to use a low specification oil to ensure that you do not over clean your engine and lose compression (for example). Generally speaking, an SAE 15W/40 diesel engine oil for about 500 miles might do the trick. WHICH OIL SHOULD YOU BUY? (THE SHORT VERSION) That all depends on your car, your pocket and how you intend to drive and service the car. All brands claim theirs offers the best protection available - until they launch a superior alternative. It's like washing powders - whiter than white until new Super- Nukem-Dazzo comes out. For most motorists and most cars, a quality mainstream oil is the best, like Castrol GTX. Moving up a step, you could look at Duckhams QXR and Castrol Protection Plus and GTX3 Lightec. The latter two of these are designed specifically for engines with catalytic converters. They're also a good choice for GTi's and turbo engines. Go up a step again and you're looking at synthetic oils aimed squarely at the performance market like Mobil-1. To help you through the maze of oils available, there's a site available now (the motor oil evaluator) that aims to lessen the confusion with a relatively balanced scoring system based on published specifications such as viscosity and pour point. It's a good starting point if you're looking for even more in-depth info. WHICH OIL SHOULD YOU BUY? (THE LONG VERSION) Quality Counts! It doesn't matter what sort of fancy marketing goes into an engine oil, or how many naked babes smear it all over their bodies, or how bright and colourful the packaging is, it's what's written on the packaging that counts. Specifications and approvals are everything. There are two established testing bodies. The API (American Petroleum Institute), and the European counterpart, the ACEA (Association des Constructeurs Europeens d'Automobiles - replaced CCMC in 1996). You've probably never heard of either of them, but their stamp of approval will be seen on the side of every reputable can of engine oil. The API The API classifications are different for petrol and diesel engines: For petrol, listings start with 'S' (meaning Service category, but you can also think of it as Spark- plug ignition), followed by another code to denote standard. 'SN' is the current top grade but 'SH' is still the most popular. For diesel oils, the first letter is 'C' (meaning Commercial category, but you can also think of it as Compression ignition). 'CJ' is the highest grade at the moment, (technically CJ-4 for heavy-duty) but 'CH' is the most popular and is well adequate for passenger vehicle applications. Note: Castrol recently upgraded all their oils and for some reason, Castrol diesels now use the 'S' rating, thus completely negating my little aid-memoire above. So the older CC,CD,CE and CF ratings no longer exist, but have been replaced by an 'SH' grade diesel oil. This link is a service bulletin from Castrol, explaining the situation.
The CCMC/ACEA The ACEA standards are prefixed with an 'A' for petrol engines, 'B' for passenger car diesel, 'C' for diesel with particulate filter, or 'E' for heavy-duty diesel. (The older CCMC specifications were G,D and PD respectively). The ACEA grades may also be followed by the year of issue which will be either '04 or '07 (current). Coupled with this are numerous approvals by car manufacturers which many oil containers sport with pride.
The full ACEA specs are: . A1 Fuel Economy Petrol † . A2 Standard performance level . A3 High performance and / or extended drain . A5 Fuel economy petrol with extended drain capability † . B1 Fuel Economy diesel † . B2 Standard performance level (now obsolete) . B3 High performance and / or extended drain . B4 For direct injection passenger car diesel engines . B5 Fuel economy diesel with extended drain capability † † Not suitable for all engines - should ONLY be used in engines specifying this fuel efficient grade. Refer to the manufacturer handbook of contact your local dealer if you're not sure. Mineral oils: . E1 Non-turbo charged light duty diesel . E2 Standard performance level . E3 High performance extended drain . E5 (1999) High performance / long drain plus American/API performances. - This is ACEAs first attempt at a global spec. . E7 Euro 4 engines - exhaust after treatment (EGR / SCR) Part / full synthetic oils: . E4 Higher performance and longer extended drain . E6 Euro 4 specification - low SAPS for vehicles with PDF (see below) Low SAPS diesel (Sulphated Ash, Phosphorous, Sulphur): For diesel engines fitted with a diesel particulate filter (DPF) - a filter unit in the exhaust that takes out the microscopic soot particles. Regular diesel oils used in engines that have a DPF can cause the filter to become blocked with ash. . C1 Low SAPS (0.5% ash) fuel efficient . C2 Mid SAPS (0.8% ash) fuel efficient, performance . C3 Mid SAPS (0.8% ash) Many OEM are now using their own specifications to capture these specifications. eg. Mercedes 229.31/51, BMW Longlife 04, VW 507 00 etc. There is also a trend now towards manufacturers requiring their own specifications - in this case the OEM specification is the one that needs to be adhered to. If it says BMW Longlife 04, the oil must say this on the pack to be suitable for use. Typically, these markings will be found in a statement similar to: Meets the requirements of API SH/CD along the label somewhere. Also, you ought to be able to see the API Service Symbol somewhere on the packaging:
BEWARE THE FAKE API SYMBOL
Some unscrupulous manufacturers (and there's not many left that do this) will put a symbol on their packaging designed to look like the API symbol without actually being the API symbol. They do this in an effort to pump up the 'quality' of their product by relying on people not really knowing exactly what the proper API symbol should look like. To the left is an example of a fake symbol - it looks similar but as long as you remember what to look for, you won't get taken by this scam. Amsoil are one of the biggest inadvertent offenders of the fake API symbol. Take a look at one of their labels here on the right. See that little starburst that says "Fuel efficient formula SL-CF"? It's actually not an API-certified SL or CF oil. (To be fair, some Amsoil products are API certified and they do have the correct labelling, but their top-tier products do not). The issue of their lack of API certification on these products caused such a stir at Amsoil that they had to generate a FAQ to answer the most commonly- asked questions. You can find a copy of that here : Amsoil & API Licensing. It explains everything logcially and clearly, and it's not scientific doublespeak. Which is nice. A Brief History of API ratings Some people have asked about the old standards, and although they're not especially relevant, some rampant plagiarism from an API service bulletin means I can bring you all the API ratings right back from when the earth was cooling. the table below to see the ratings. Petrol Engines Diesel Engines Categor Categor y Status Service y Status Service Introduced in 2006 for high-speed four-stroke engines. Designed to meet 2007 on-highway exhaust emission standards. CJ-4 oils are compounded for use in all applications with diesel fuels ranging in sulphur content up to500ppm (0.05% by weight). However, use of these oils with greater than 15ppm sulfur fuel may impact exhaust aftertreatment system durability and/or oil drain intervals. CJ-4 oils are effective at sustaining emission control system durability where particulate filters and other advanced For all automotive aftertreatment systems engines presently in use. are used. CJ-4 oils Introduced in the API exceed the performance service symbol in criteria of CF-4, CG-4, SN Current November 2010 CJ-4 Current CH-4 and CI-4. SM Current For all automotive CI-4 Current Introduced in 2002 for engines presently in use. high-speed four-stroke Introduced in the API engines. Designed to service symbol in meet 2004 exhaust November 2004 emission standards implemented in 2002. CI-4 oils are formulated to sustain engine durability where exhaust gas recirculation (EGR) is used and are intented for use with diesel fuels ranging in sulphur content up to 0.5% weight. Can be used in place of CD, CE, CF-4, CG-4 and CH-4 Introduced in 1998 for high-speed four-stroke engines. CH-4 oils are specifically designed for use with diesel fuels Still ranging in sulphur current For all automotive content up to 0.5% but engines presently in use. weight. Can be used in nearly Introduced in the API place of CD, CE, CF-4 SL obsolete service symbol in 1998 CH-4 Current and CG-4. Introduced in 1995 for high-speed four-stroke engines. CG-4 oils are specifically designed for use with diesel fuels ranging in sulphur content less than 0.5% weight. CG-4 oil needs Still to be used for engines current For all automotive meeting 1994 emission but engines presently in use. standards. Can be used nearly Introduced in the API in place of CD, CE and SJ obsolete service symbol in 1996 CG-4 Current CF-4. Introduced in 1990 for high-speed four-stroke naturally aspirated and turbo engines. Can be Obsolet For model year 1996 used in place of CD and SH e and older engines. CF-4 Current CE. Introduced in 1994 for severe duty, two stroke motorcycle engines. Can Obsolet For model year 1993 be used in place of CD- SG e and older engines. CF-2 Current II. Introduced in 1994 for off-road, indirect- injected and other diesel engines including those using fuelover0.5% Obsolet For model year 1988 weight sulphur. Can be SF e and older engines. CF Current used in place of CD. SE Obsolet For model year 1979 CE Obsolet Introduced in 1987 for high-speed four-stroke naturally aspirated and turbo engines. Can be used in place of CC and e and older engines. e CD. Introduced in 1987 for Obsolet For model year 1971 Obsolet two-stroke motorcycle SD e and older engines. CD-II e engines. Introduced in 1955 for certain naturally Obsolet For model year 1967 Obsolet aspirated and turbo SC e and older engines. CD e engines. For older engines. Use this only when specifically Obsolet recommended by the Obsolet Introduced in 1961 for SB e manufacturer. CC e all diesels. For much older engines with no performance requirement. Use this only when specifically Obsolet recommended by the Obsolet Introduced in 1949 for SA e manufacturer. CB e moderate-duty engines. Obsolet Introduced in 1940 for CA e light-duty engines.
Grade counts too!The API/ACEA ratings only refer to an oil's quality. For grade, you need to look at the SAE (Society of Automotive Engineers) ratings. These describe the oil's function and viscosity standard. Viscosity means the substance and clinging properties of the lubricant. When cold, oil can become like treacle so it is important that any lube is kept as thin as possible. Its cold performance is denoted by the letter 'W', meaning 'winter'. At the other end of the scale, a scorching hot oil can be as thin as water and about as useful too. So it needs to be as thick as possible when warm. Thin when cold but thick when warm? That's whereMultiGrade oil comes in. For ages, good old 20W/50 was the oil to have. But as engines progressed and tolerances decreased, a lighter, thinner oil was required, especially when cold. Thus 15W/50, 15W/40 and even 15W/30 oils are now commonplace. THE QUESTION OF PHOSPHORUS AND ZINC. Phosphorus (a component of ZDDP - Zinc Dialkyl-Dithio-Phosphate) is the key component for valve train protection in an engine and 1600ppm (parts per million) used to be the standard for phosphorus in engine oil. In 1996 the EPA forced that to be dropped to 800ppm and then more recently (2004?) to 400ppm - a quarter of the original spec. Valvetrains and their components are not especially cheap to replace and this drop in phosphorus content has been a problem for many engines (especially those with flat-tappet type cams). So why was the level dropped? Money. Next to lead, it's the second most destructive substance to shove through a catalytic converter. The US government mandated a 150,000 mile liftime on catalytic converters and the quickest way to do that was to drop phosphorous levels and bugger the valvetrain problem. Literally. In the US, Mobil 1 originally came out with the 0W40 as a 'European Formula' as it was always above 1000 ppm. This initially got them out of the 1996 800ppm jam and knowledgeable consumers sought it out for obvious reasons. Their 15W50 has also maintained a very high level of phosphorus and all of the extended life Mobil synthetics now have at least 1000ppm. How do they get away with this? They're not classified as energy/fuel conserving oils and thus do not interfere with the precious government CAFE (corporate average fuel economy) ratings. (See my section on the EPA and fuel economy in the Fuel and Engine Bible for more info on this). This also means that they don't get the coveted ratings of other oils but they do protect your valvetrain. The same rule of thumb is true for racing oils like Royal Purple - because they're not classified as energy / fuel conserving, it would seem they still contain good quantities of ZDDP. Royal Purple is a popular oil for Mustang enthusiasts, as it's formulated for performance vehicles that are looking to maximize results at the track or drag strip. In fact, as a general rule-of-thumb, staying away from XX-30 oils and going to 10W-40 or higher might be the way to go if you have an older engine. 10W-40 and above is generally also not considered to be 'gas saving' and like the Mobil example above, doesn't mess with the CAFE rating. If you live in England, Castrol market a product with ZDDP in the product description - 'Castrol Classic Oil With ZDDP Anti-Wear Additive' although it's not mainstream enough to be available everywhere. You'll have to find a specialist dealer. Castrol Classics. In the US, Rislone manufacture an oil supplement to boost the ZDDP content of your existing oil. Rislone Engine Oil Supplement. API RATING BACKWARD COMPATIBILITY AND 2V ENGINES This section contains information from Bruce Dance, Brian over at bigcoupe.com and LN Engineering and their combined experience with API ratings and 2 valve engines If you own a two-valve spark ignition engine or certain diesel engines (which do not have to meet recent emission standards) the only sensible (ie widely available) oil to put in right now is synthetic or semisynthetic to meet API SL/CF and not a higher rating. As I touched upon above, oils with a CG and higher rating typically don't contain enough ZDDP, and the replacement friction modifiers don't work in highly loaded valve trains (generally older engines especially those with 2V design). If you try to compensate by adding a ZDDP additive into a newer oil it still might not work because of interactions with other additives in the oil. Why the discrepancy in the ratings? The API no longer include a valve train wear test that accurately simulates 2V cam follower loading. They do perform a test that simulates 4V loading and then they allow a lot of wear to occur and still 'pass'. The ACEA tests are a lot tougher but still not tough enough. Whilst the newer CG, CH and higher API oil standards should be 'better in every way', they are really just 'improved in some ways'. Hence the increasing use of manufacturer-specific standards. There is a lot of info kicking around on the web on this topic because it has caused a LOT of problems with some engines especially Porsche aircooled units. One of my readers found out when he went to buy oil for his (modern 4V common rail diesel) Nissan that they expressly prohibit the use of CG or higher rated oils. Nissan mandate that owners use CF oils in these engines. It's worth noting that the CF spec was already out of date when these engines were built but Nissan did not use the latest API spec because it wasn't good enough! The fact that API have dropped the CF tests/standard does not in any way improve the later oils that do not meet this standard. MARINE DIESELS AND OTHER SPECIAL CONSIDERATIONS. Inland Marine Diesels (and certain road vehicles under special conditions) can (and do) glaze their bores due the low cylinder wall temperatures causing the oil (and more importantly the additive pack) to undergo a chemical change to a varnish-like substance. The low temperature is caused by operating under light load for long periods. This is related to engine design, some engines being nearly immune to it and others susceptible. The old Sherpa van diesel engines were notorious for this problem. The "cure" (such as it is) is to use a low API specification oil, such as CC. Certain engine manufacturers/marinisers are now marketing the API CC oil for this purpose under their own name (and at a premium). You'll find some modern engines where its industrial/vehicle manual states API CF and the marinised manual states API CC/CD. {Thanks to Tony Brooks for this information.} MARINE OILS. I sometimes get asked "why are marine engine oils so expensive and why can't I just use regular motor oil in my marine engine instead?". Well, the National Marine Manufacturers Association Oil Certification Committee (click here for more info) introduced a four-stroke engine oil test and standard called the 4T certification. This specification is meant to assist boaters and manufacturers in identifying four-stroke cycle engine oils that have been specially formulated to withstand the rigors of marine engine operation. The certification was prompted by the growing influence of four-stroke engines in the marine market and their unique lubrication demands. So the simple answer is that regular road-based engine oil products don't contain rust inhibitors and won't pass the 4T certification. Lakes, waterways and the sea are a lot more aggressive an environment for an engine to operate around than on land. Note : the NMMA have long had a similar specification for 2-stroke oils destined for marine use, called the TC-W3® certification. THE EBAY PROBLEM This paragraph may seem a little out of place but I have had a lot of problems with a couple of eBay members (megamanuals and lowhondaprelude) stealing my work, turning it into PDF files and selling it on eBay. Generally, idiots like this do a copy/paste job so they won't notice this paragraph here. If you're reading this and you bought this page anywhere other than from my website at www.carbibles.com, then you have a pirated, copyright-infringing copy. Please send me an email as I am building a case file against the people doing this. Go to www.carbibles.com to see the full site and find my contact details. And now, back to the meat of the subject....
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ENGINE OIL / MOTOR OIL SHELF LIFE. I couldn't decide whether to put this in the FAQ or the main page, so it's in both, because I get asked this question a lot. Typically, the question is along the lines of "GenericAutoSuperStore are having a sale on WickedlySlippy Brand synthetic oil. If I buy it now, how long can I keep if before I use it?" In general, liquid lubricants (ie. oils, not greases) will remain intact for a number of years. The main factor affecting the life of the oil is the storage condition for the products. Exposure to extreme temperature changes, and moisture will reduce the shelf life of the lubricants. (an increase of 10°C doubles oxidation which halves the shelf life) ie. don't leave it in the sun with the lid off. Best to keep them sealed and unopened.
Technically, engine oils have shelf lives of four to five years. However, as years pass, unused engine oils can become obsolete and fail to meet the technical requirements of current engines. The specs get updated regularly based on new scientific testing procedures and engine requirements. But this is only really a concern if you've bought a brand new car but have engine oil you bought for the previous car. An oil that is a number of years old might not be formulated to meet the requirements set for your newer engine. If your unopened containers of engine oil are more than three years old, read the labels to make sure they meet the latest industry standards. If they do meet the current standards, you might want to take the extra precaution of obtaining oil analysis before using them. An oil analysis will check for key properties of the oil and ensure that it still meets the original manufacturing specs. Of course the cost of getting an analysis done on old oil is probably going to outweigh going and buying fresh stuff. So it's a double- edged sword. As a general rule, the simpler the oil formulation, the longer the shelf life. The following is a guideline under protected conditions - indoors at about 20°C: Product Shelf Life Base Oils, Process Oils 3 years Hydraulic Oils, Compressor Oils, General Purpose Lubricating Oils 2 years Engine Oils and Transmission Oils 3 years Industrial and Automotive Gear Oils 2 years Metal Working and Cutting Oils 1 year The following are signs of storage instability in a lubricant: . Settling out of the additives as a gel or sticky liquid . Floc or haze . Precipitates/solid material . Colour change or haziness Water contamination in a lubricant can be detected by a "milky" appearance of the product. Next page More and more oil companies are coming out with "high mileage" oils, some recommended for engines with as few as 75,000 miles on them. So what is a "high mileage" oil you ask? Very generally speaking, these oils have two additives in them that are more suited to older engines. The first is normally a burnoff-inhibitor which helps prevent the oil from burning off if it gets past an engine seal into the combustion chamber. The second is a "seal conditioner", the exact makeup of which I'm not sure of, but it's designed to soak into seals such as head- and rocker-cover gaskets and force them to expand. Thus if one of the seals is a bit leaky, the seal conditioner will attempt to minimise the leak. I've not had experience of high mileage oils myself, but a few people who've e-mailed me have passed on various tales from it being the miracle cure to it making no difference at all. I think the general rule-of-thumb though should be "if it 'aint broke, don't fix it." Just because your engine has over 75,000 miles on it, doesn't automatically mean you need high mileage oil. Is the exhaust sooty or smokey? Are you noticing oil leaks? Is the engine consuming oil? If your engine is working fine, the exhaust is clean and you're not noticing any problems, my guess is that it doesn't need high-mileage oil.
WHAT ABOUT OWN-BRANDS?
If you can't afford the big-name players, you could look at own-brand oils. These are usually badged oils from one of the larger companies but sold without the name, they are cheaper. Check the standards and grade ratings on the pack first! The example on the left is a local store in Chelmsford in England who sell their own label oil which is bottled for them by a volume retailer. The label tells you all you need to know. THE BRAKE BIBLE WHAT DO BRAKES DO? The simple answer: they slow you down. The complex answer: brakes are designed to slow down your vehicle but probably not by the means that you think. The common misconception is that brakes squeeze against a drum or disc, and the pressure of the squeezing action is what slows you down. This in fact is only part of the equation. Brakes are essentially a mechanism to change energy types. When you're travelling at speed, your vehicle has kinetic energy. When you apply the brakes, the pads or shoes that press against the brake drum or rotor convert that energy into thermal energy via friction. The cooling of the brakes dissipates the heat and the vehicle slows down. It's the First Law of Thermodynamics, sometimes known as the law of conservation of energy. This states that energy cannot be created nor destroyed, it can only be converted from one form to another. In the case of brakes, it is converted from kinetic energy to thermal energy. Angular force. Because of the configuration of the brake pads and rotor in a disc brake, the location of the point of contact where the friction is generated also provides a mechanical moment to resist the turning motion of the rotor. THERMODYNAMICS, BRAKE FADE AND DRILLED ROTORS. Picture credit: Formula1.com
If you ride a motorbike or drive a race car, you're probably familiar with the term brake fade, used to describe what happens to brakes when they get too hot. A good example is coming down a mountain pass using your brakes rather than your engine to slow you down. As you start to come down the pass, the brakes on your vehicle heat up, slowing you down. But if you keep using them, the rotors or drumsstay hot and get no chance to cool off. At some point they can't absorb any more heat so the brake pads heat up instead. In every brake pad there is the friction material that is held together with some sort of resin and once this starts to get too hot, the resin starts to vapourise, forming a gas. Because the gas can't stay between the pad and the rotor, it forms a thin layer between the two whilst trying to escape. The pads lose contact with the rotor, reducing the amount of friction and voila. Complete brake fade. The typical remedy for this would be to get the vehicle to a stop and wait for a few minutes. As the brake components cool down, their ability to absorb heat returns and the next time you use the brakes, they seem to work just fine. This type of brake fade was more common in older vehicles. Newer vehicles tend to have less outgassing from the brake pad compounds but they still suffer brake fade. So why? It's still to do with the pads getting too hot. With newer brake pad compounds, the pads transfer heat into the calipers once the rotors are too hot, and the brake fluid starts to boil forming bubbles in it. Because air is compressible (brake fluid isn't) when you step on the brakes, the air bubbles compress instead of the fluid transferring the motion to the brake calipers. Voila. Modern brake fade.
So how do the engineers design brakes to reduce or eliminate brake fade? For older vehicles, you give that vapourised gas somewhere to go. For newer vehicles, you find some way to cool the rotors off more effectively. Either way you end up with cross-drilled or grooved brake rotors. While grooving the surface may reduce the specific heat capacity of the rotor, its effect is negligible in the grand scheme of things. However, under heavy braking once everything is hot and the resin is vapourising, the grooves give the gas somewhere to go, so the pad can continue to contact the rotor, allowing you to stop.
The whole understanding of the conversion of energy is critical in understanding how and why brakes do what they do, and why they are designed the way they are. If you've ever watched Formula 1 racing, you'll see the front wheels have huge scoops inside the wheel pointing to the front (see the picture above). This is to duct air to the brake components to help them cool off because in F1 racing, the brakes are used viciously every few seconds and spend a lot of their time trying to stay hot. Without some form of cooling assistance, the brakes would be fine for the first few corners but then would fade and become near useless by half way around the track. ROTOR TECHNOLOGY. If a brake rotor was a single cast chunk of steel, it would have terrible heat dissipation properties and leave nowhere for the vapourised gas to go. Because of this, brake rotors are typically modified with all manner of extra design features to help them cool down as quickly as possible as well as dissapate any gas from between the pads and rotors. The diagram here shows some examples of rotor types with the various modification that can be done to them to help them create more friction, disperse more heat more quickly, and ventilate gas. From left to right.
1: Basic brake rotor. 2: Grooved rotor - the grooves give more bite and thus more friction as they pass between the brake pads They also allow gas to vent from between the pads and the rotor. 3: Grooved, drilled rotor - the drilled holes again give more bite, but also allow air currents (eddies) to blow through the brake disc to assist cooling and ventilating gas. 4: Dual ventilated rotors - same as before but now with two rotors instead of one, and with vanes in between them to generate a vortex which will cool the rotors even further whilst trying to actually 'suck' any gas away from the pads. An important note about drilled rotors: Drilled rotors are typically only found (and to be used on) race cars. The drilling weakens the rotors and typically results in microfractures to the rotor. On race cars this isn't a problem - the brakes are changed after each race or weekend. But on a road car, this can eventually lead to brake rotor failure - not what you want. I only mention this because of a lot of performance suppliers will supply you with drilled rotors for street cars without mentioning this little fact. Certain cars require more upgrading for brakes than others. Mustangs happen to be one of those vehicles. AmericanMuscle does a great job explaining the Mustang braking system and how to go about upgrading from the stock form. BIG ROTORS. How does all this apply to bigger brake rotors - a common sports car upgrade? Sports cars and race bikes typically have much bigger discs or rotors than your average family car. A bigger rotor has more material in it so it can absorb more heat. More material also means a larger surface area for the pads to generate friction with, and better heat dissipation. Larger rotors also put the point of contact with the pads further away from the axle of rotation. This provides a larger mechanical advantage to resist the turning of the rotor itself. To best illustrate how this works, imagine a spinning steel disc on an axle in front of you. If you clamped your thumbs either side of the disc close to the middle, your thumbs would heat up very quickly and you'd need to push pretty hard to generate the friction required to slow the disc down. Now imagine doing the same thing but clamping your thumbs together close to the outer rim of the disc. The disc will stop spinning much more quickly and your thumbs won't get as hot. That, in a nutshell explains the whole principle behind why bigger rotors = better stopping power.
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THE DIFFERENT TYPES OF BRAKE. All brakes work by friction. Friction causes heat which is part of the kinetic energy conversion process. How they create friction is down to the various designs. BICYCLE WHEEL BRAKES
I thought I'd cover these because they're about the most basic type of functioning brake that you can see, watch working, and understand. The construction is very simple and out-in-the-open. A pair of rubber blocks are attached to a pair of calipers which are pivoted on the frame. When you pull the brake cable, the pads are pressed against the side or inner edge of the bicycle wheel rim. The rubber creates friction, which creates heat, which is the transfer of kinetic energy that slows you down. There's only really two types of bicycle brake - those on which each brake shoe shares the same pivot point, and those with two pivot points. If you can look at a bicycle brake and not understand what's going on, the rest of this page is going to cause you a bit of a headache.
DRUM BRAKES - SINGLE LEADING EDGE The next, more complicated type of brake is a drum brake. The concept here is simple. Two semicircular brake shoes sit inside a spinning drum which is attached to the wheel. When you apply the brakes, the shoes are expanded outwards to press against the inside of the drum. This creates friction, which creates heat, which transfers kinetic energy, which slows you down. The example below shows a simple model. The actuator in this case is the blue elliptical object. As that is twisted, it forces against the brake shoes and in turn forces them to expand outwards. The return spring is what pulls the shoes back away from the surface of the brake drum when the brakes are released. See the later section for more information on actuator types.
The "single leading edge" refers to the number of parts of the brake shoe which actually contact the spinning drum. Because the brake shoe pivots at one end, simple geometry means that the entire brake pad cannot contact the brake drum. The leading edge is the term given to the part of the brake pad which does contact the drum, and in the case of a single leading edge system, it's the part of the pad closest to the actuator. This diagram (right) shows what happens as the brakes are applied. The shoes are pressed outwards and the part of the brake pad which first contacts the drum is the leading edge. The action of the drum spinning actually helps to draw the brake pad outwards because of friction, which causes the brakes to "bite". The trailing edge of the brake shoe makes virtually no contact with the drum at all. This simple geometry explains why it's really difficult to stop a vehicle rolling backwards if it's equipped only with single leading edge drum brakes. As the drum spins backwards, the leading edge of the shoe becomes the trailing edge and thus doesn't bite. DRUM BRAKES - DOUBLE LEADING EDGE
The drawbacks of the single leading edge style of drum brake can be eliminated by adding a second return spring and turning the pivot point into a second actuator. Now when the brakes are applied, the shoes are pressed outwards at two points. So each brake pad now has one leading and one trailing edge. Because there are two brake shoes, there are two brake pads, which means there are two leading edges. Hence the name double leading edge.
DISC BRAKES Some background. Disc brakes were invented in 1902 and patented by Birmingham car maker Frederick William Lanchester. His original design had two discs which pressed against each other to generate friction and slow his car down. It wasn't until 1949 that disc brakes appeared on a production car though. The obscure American car builder Crosley made a vehicle called the Hotshot which used the more familiar brake rotor and calipers that we all know and love today. His original design was a bit crap though - the brakes lasted less than a year each. Finally in 1954 Citroën launched the way-ahead-of-its-time DS which had the first modern incarnation of disc brakes along with other nifty stuff like self-levelling suspension, semi-automatic gearbox, active headlights and composite body panels. (all things which were re-introduced as "new" by car makers in the 90's). Disc brakes are an order of magnitude better at stopping vehicles than drum brakes, which is why you'll find disc brakes on the front of almost every car and motorbike built today. Sportier vehicles with higher speeds need better brakes to slow them down, so you'll likely see disc brakes on the rear of those too.
Disc brakes are again a two-part system. Instead of the drum, you have a disc or rotor, and instead of the brake shoes, you now have brake caliper assemblies. The caliper assemblies contain one or more hydraulic pistons which push against the back of the brake pads, clamping them together around the spinning rotor. The harder they clamp together, the more friction is generated, which means more heat, which means more kinetic energy transfer, which slows you down. You get the idea by now.Visit http://www.carid.com/brakes.html to find more brakes for your vehicle. Standard disc brakes have one or two cylinders in them - also know as one or two-pot calipers. Where more force is required, three, or more cylinders can be used. Sports bikes have 4- or 6-pot calipers arranged in pairs. The disadvantage of disc brakes is that they are extremely intolerant of faulty workmanship or bad machining. If you have a regular car disc rotor which is off by so much as 0.07mm (3/1000 inch) it will be Hell when you step on the brakes. That ever-so-slight warp or misalignment is going to spin through the clamped calipers at some ungodly speed and the resulting vibration will make you wonder if you're driving down stairs. To combat this problem, which is particularly critical on motorbikes, floating rotors were invented. THE FLOATING ROTOR. Standard brake rotors are cast in a single piece which bolts directly to the wheel or drive plate. If the mounting surface of your wheel or drive plate isn't perfectly flat, you'll get vibration at speed. Floating rotors are typically cast in two pieces - the rotor and the carrier. The carrier is bolted to the wheel and the rotor is attached to the carrier using float buttons. The other method of floating a brake rotor is to have the rotor bolted directly to the wheel itself without a carrier, but the bolts have float buttons built into them. These buttons allow the brake rotor some freedom to move laterally, but restrict the angular and rotational movement as if they were bolted directly to the wheel. This slight lateral motion (which can be less than 0.03mm) is just enough to prevent vibration in the brake system. As the calipers are mounted solidly, any warping or misalignment in the wheel or brake rotor mounting face can be compensated for because the rotor will "float" laterally on the float buttons. This side-to-side vibration is separated from the carrier by the float buttons themselves, so none of the resulting motion is transferred into the suspension or steering. Clever eh? The rendering to the right shows an extreme close-up of the brake disc shown above. I've rendered the components slightly transparent so you can see what's going on. RADIAL CALIPERS / RADIAL BRAKES. Around 2003, motorbikes started to hit the showrooms with a new feature - radial brakes. The magazines and testers will all tell you that radial brakes make the bike stop quicker. Not true - they have nothing to do with stopping power and everything to do with the design of the front forks of the bike. More and more bikes are coming out with upside-down forks. ie. instead of the fat canister part of the fork being at the bottom of the assembly, it's at the top. This means that the fork pistons are now the part of the suspension with the wheel attached to them. It also means that it's impossible to put a stiffening fork brace down there now because the brace would need to move with the wheel, and the length of the fork pistons precludes that. The stiffness of the front end is now entirely dependent on the size of the front axle. Bigger axle = stiffer front end. A side-effect of this design was that traditionally-mounted brake calipers could cause a lot of vibration in the steering because of flex between the wheel (with the brake disc bolted to it), and the fork leg (with the caliper). The slight tolerance allowed by floating brake rotors couldn't compensate for the amount of flexing in the forks. To reduce the brake-induced fork vibration, the brake calipers were moved around the rotors slightly so that they fell into the front-rear alignment of the wheel axle. There's less lateral flex at that point, which means less or no vibration. The caliper mounts were changed too. Traditional calipers bolt on to the forks with bolts going through them at 90° to the face of the brake rotor. With radial calipers, the bolts are aligned parallel to the brake rotor - effectively also in the front-rear alignment of the wheel. This design is a trickle-down technology from superbike racing where a radial caliper mount allows the racing teams to use different diameters of brake rotor by simply adding spacers between the caliper and the mounting bracket. The image here shows the difference between traditional and radially mounted brake calipers. FULL-CONTACT DISC BRAKES. There is a quiet but major revolution happening in the world of brakes, and it was being brought about by a Canadian company called NewTech. I say 'was' because whilst there is still reference to them spotted about the internet, their main site and contacts seem to have vanished. Anyway - rather than the piecemeal improvements we've seen over the last few years, with slight design changes, and materials improvements, the new system is a radical redesign from the ground up. NewTech designed a disc brake system called "full contact disc brakes". They looked at traditional pad and rotor design and figured that the pads only contact about 15% of the rotor surface at any one time. With a change of design, NewTech were been able to add 5 more pads to the system so that 75% of the brake rotor is in contact with the pads at any one time.
With traditional pads and rotors, the brake rotor is clamped between the pad. With the NewTech design, the brake rotor itself becomes a floating rotor, similar to those found on motorbikes. It is covered with a 'spider' (the red structure in my renderings) that has 6 brake pads on the inside of it. The hydraulic system acts on fully circular elastomer composite diaphragm behind the brake disc, mounted in the black structure in the renderings. This also has 6 pads on it which push the entire disc out against the 6 pads inside the spider. This provides an even force across the entire disc helping it to make even contact with all 12 pads. To ensure the brakes remain cool, the system is covered in cooling fins connected to the outer pads to dissipate heat. The inner pads are fitted with a moulded thermal barrier made of a composite material. Special inserts made of a variety of frictional materials are distributed evenly on the entire surface of the pad. The range of materials is used to ensure performance under diverse conditions. NewTech believed that the system had considerable advantages over conventional brakes with better cooling, higher strength and reduced noise and vibration. NewTech sold truck and bus versions of these brakes into the haulage and public transport industry, but now Renault is considering introducing this system on its cars in conjunction with a new brake-by-wire system. Newtech's first OEM customer was to be Saleen who were going to put the system on their S7 supercar, but in the end went with conventional six-piston monoblock calipers instead. NewTech's website went offline in 2009 and has yet to be resurrected. It's worth noting that this isn't actually the first time this has been tried in cars. Bugatti experimented with a system like this in the late 80's for inclusion on their 1991 EB110 supercar; it was going to be available as an option for the car. People who had experienced the brakes said they were just otherworldy, that the braking power was way beyond the capabilities of the average driver. They came from Aerospatiale, the French aerospace company, who also designed the chassis for the EB110 (this type of brake was being used in aircraft at the time). Bugatti dropped the idea because the brakes would have cost more than the rest of the EB110, which at $350,000 was by no means a cheap car. THE SIEMENS VDO ELECTRIC WEDGE BRAKE. Siemens VDO in Germany are trying to bring a prototype electric wedge brake (EWB) to the market. As much as it sounds like a high school prank involving underwear, it's actually the latest attempt to remove hydraulics from the braking circuit in a car. The EWB is an innovative idea based on technology developed by a company called eStop. Siemens acquired eStop early in 2005 and have been continuing their work on the wedge system ever since. The principle is both simple and clever. The brake pad is pressed against the brake rotor by means of a wedge-shaped thrust plate. The more the brake rotor turns, the harder the slope of the wedge forces the pads against it. Because of the shape of the wedge bearings and thrust plate and the rotation of the brake rotor, the pad is actually forced against the rotor harder the faster the rotor is spinning. In effect, a lot of braking force for very little input. The system runs off a normal 12v vehicle electrical system which means no more hydraulics. It also allows the system to eliminate all the plumbing associated with ABS as the EWB is entirely electronically controlled. The final advantage, if you could call it that, is that it allows the first true all-electronic brake-by-wire system. Current brake-by- wire systems use electronics behind the brake pedal to send signals to actuators in the hydraulic system. With the EWB there is no hydraulic system so the only link from the brake pedal to the brake caliper is a 12v electrical feed and signal actuation wire. The operation of the wedge system is based on several roller bearings and a wedge- shaped thrust plate connected to a pair of 12v electric motors. As the brake pedal is depressed, the signal is sent to the motors to start moving the thrust plate. Because of its shape and the design of the roller bearings, as the thrust plate moves, it forces the brake pad to press against the brake rotor. The reaction time of the electric motors can be measured in milliseconds - far quicker than any hydraulic system could react, so in theory, when connected to a full computer-monitored brake-by-wire system, the EWB ought to be able to shave milliseconds off brake reaction time. Doesn't sound like much but if it means a few less metres in stopping distance, that can only be a good thing. The brake caliper unit itself has an intelligent wheel-braking module built into it. As well as the motors, bearings and wedges, the module also has a sensor system for monitoring movement and force - basically this is what replaces the traditional ABS items so each brake caliper becomes a self-governing ABS unit. Because there's no physical link back to the brake pedal any more, the ABS doesn't force the brake pedal to judder when it activates which will make it far more acceptable for a lot more drivers. Finally, because the system is totally electronic, the traditional cable-pulled handbrake can also be eliminated and replaced with a parking switch that simply activates all four EWB modules.
Of course there are pros and cons to any new system like this. Obviously reducing the weight and complexity of the braking system is a good thing, and because of the design of the EWB, there's a lot less space taken up in the engine bay, freeing up more room for the car designers to work with. But by removing the hydraulic lines, ABS actuators and sensors, and master and slave brake cylinders, the EWB concept becomes entirely reliant on the 12v electrical system and the vagaries of a computer. Knowing how often a single dodgy earth connections in a car can totally screw up the electrics, I've got to wonder what would happen if a grounding strap came loose and the electronic brake system started playing up. Will these brakes have a fail-safe or backup system like the double hydraulic circuits we use now, or will you sail off into some solid object because you've got no brakes left? Siemens aren't clear on this matter. Until I get the chance to render up some illustrations of my own to better show how the system works, the one you see here is from the Siemens press pack. If you want to see a video demonstrating the EWB, Siemens VDO have oneavailable here (27.8Mb mpeg). Picture credit: Siemens press kit BRAKE PAD COMPOUNDS. Just a quick word on brake pad compounds. Most pads used to use asbestos but we all know what that stuff is like. Today they use all manner of combinations of materials. The pads themselves are made up of a friction material bonded to the backing plate. The brake caliper piston pushes against the backing plate and the friction material is pushed against the brake rotor. The material combinations typically fall into the following broad categories now. Organic These pads are well-suited for street driving because they wear well, are easy on the ears, don't chew up the rotors and don't spew dust everywhere. They're favoured for your average family saloon because they work well when they're cold. Of course the drawback is that they don't work so well when they get hot. Semi-metallic / sintered This is a good compromise between street and track. These seem to be the pad of choice for sportier vehicles such as the Subaru Impreza WRX. They won't work as well as organic pads when they are cold, so you need to be a bit wary of the first couple of stops. Conversely they do work well when hot. Occasionally the weak link in semi-metallic pads is the bonding material that holds the friction pad to the backing plate. There have been occasions where the friction material has come away completely. That's infrequent though. Metallic These pads are typically reserved for racing or the extremely rich. They squeal and dust like crazy, are hard on rotors and don't work well when cold. Ceramic Ceramic pads still have metal fibres (about 15% vs. about 40% for semi- metallic) but they are copper instead of steel and therefore cause less wear and transfer heat better. They don't fade as easily as other pads, cool faster, last longer, and are effectively silent, as the sound they genereate is outside of the human range of hearing. Dogs will go crazy though. The dust created by ceramic pads is also very light in color so your wheels look cleaner. BRAKE SQUEAL. Squealing brakes are a sign of one of two things : the friction material is all gone and you're jamming the backing plate against the brake rotor, or the fit of the brake pad against the caliper piston isn't as snug as it could be. Either way, the squealing is the result of an extremely high-frequency vibration between the pad, the caliper piston and the brake rotor. Some vehicles have problems with squealy brakes right from the factory. In those cases, simply changing brake pad manufacturer can often cure the problem as the different pads will have a slightly different harmonic frequency, which is harder to attain. A classic example was one of the BMW R1100 touring bikes. From the factory, they'd squeal like crazy, and BMW redesigned the brake calipers and rotors a couple of times until they finally just switched to a different brand of pads and the problem vanished. SOLVING BRAKE SQUEAL.
If you are a reasonably competent home mechanic, then a good way to solve brake squeal is to put some copper-based grease on the back of your brake pads. That's very important so I'll say it again in CAPS : THE BACK. Copper grease is extremely resistant to pressure and heat and if you get any on the front of your pads, you'll need new pads and rotors or discs. (The picture here shows a cutaway of a disc brake assembly. The red caliper housing on the right is missing to show the two silver brake pistons.) The idea is that it creates a small pocket of sticky lubrication between the front side of the brake pistons and the back side of the brake pads. This is usually enough to prevent the high-frequency squeal. If you're not happy doing this yourself (working on a safety- critical part of your car like the brakes isn't something just everybody should be doing) then ask your friendly greasemonkey to do it for you.
There's a few products on the market that I've heard of and/or used in the past. Noisefree is one of them CRC Disc Brake Quiet is another and then there's Copaslip. I've used Copaslip on my vehicles before with no problems. I've had positive reviews of the CRC product from people using it motorbikes and cars. Noisefree is a new player so if you've used their product and have any comments, drop me a line. All three are available in America, but I think if you're in Europe you're limited to Copaslip. Or the internet of course. COPPER GREASE AND RUBBER Whilst copper grease such as Copaslip works well in the short term to solve brake squeal, long-term, it has an adverse affect on the rubber dust seals of the caliper pistons. This can lead to the seal deteriorating or failing completely. If that happens, it leaves the piston and it's surface exposed to the very elements from which it should be protected. Just so you know. THE OTHER SOLUTION TO BRAKE SQUEAL Whilst the ultra high frequency vibration is one cause of brake squeal, the other biggie is related to suspension alignment. Driving on badly-maintained roads, mountaineering through pot-holes or kerbing your wheels all make the suspension move around in ways it was never really designed to cope with, and this in turn leads to the suspension bushes becoming stressed. Normally, re-aligning the wheels on a vehicle is corrected by mechanical adjustment only. If the mounting rubbers are not de-stressed first, then it leads to the transfer of the sound generated during braking into the chassis and body which then amplifies it to where we can hear it. Sort of like a giant record player with the suspension as the pickup needle and the entire car as the speaker. If you have squealing brakes that copper grease doesn't solve, look into a proper suspension realignment and possibly new suspension bushes. THE EBAY PROBLEM This paragraph may seem a little out of place but I have had a lot of problems with a couple of eBay members (megamanuals and lowhondaprelude) stealing my work, turning it into PDF files and selling it on eBay. Generally, idiots like this do a copy/paste job so they won't notice this paragraph here. If you're reading this and you bought this page anywhere other than from my website at www.carbibles.com, then you have a pirated, copyright-infringing copy. Please send me an email as I am building a case file against the people doing this. Go to www.carbibles.com to see the full site and find my contact details. And now, back to the meat of the subject.... BRAKE ACTUATORS. Brakes are all well and good, but you need some method of applying them in order for them to work. The method by which the force from your hand or foot reaches the brake itself is all to do with the brake actuator system. CABLE-OPERATED This is about as basic as you get. A cable is connected to a lever at each end. You press on one lever with your foot or squeeze it with your hand, and it pulls the lever at the other end. On the back of the brake-end lever there's an elliptical cam which rotates inside a circular cup in the brake shoe. As the long axis of the ellipse rotates, it forces the brake shoes to move apart. In the case of a bicycle brake, the brake-end of the cable just pulls the two calipers together. SOLID BAR CONNECTION One step up, and found on the rear brake of older motorbikes, the solid bar connection. This allows the use of mechanical advantage (see below) to amplify your force on the pedal or lever before it gets to the brakes themselves. Typically these systems are used on drum brakes with the elliptical actuator described above. The disadvantage of this system is that it needs hinge and pivot points that match the position of the suspension components. If they're not present, going over a bump could put the brakes on as the suspension moves relative to the lever.
SINGLE-CIRCUIT HYDRAULIC Another step up and we get to the type of brake system used on most cars and motorbikes today. Gone are the cables and bars, replaced instead with a system of plungers, reservoirs and hydraulic fluid. Single-circuit hydraulic systems have three basic components - the master cylinder, the slave cylinder and the reservoir. They're joined together with hydraulic hose and filled with a non-compressible hydraulic fluid (see brake fluid below). When you press your foot on the brake, or squeeze the brake lever, you compress a small piston assembly in the master cylinder. Because the brake fluid does not compress, that pressure is instantaneously transferred through the hydraulic brake line to the slave cylinder where it acts on another piston assembly, pushing it out. That slave assembly is either connected to a lever to activate the brakes, or more commonly, is the brake caliper itself, with the slave cylinder being the piston that acts directly on the brake pads. Because of the arrangement of the slave cylinder, heat from the brakes can be transferred back into the brake fluid.
DUAL-CIRCUIT HYDRAULIC Dual-circuit hydraulic systems are available on high-end luxury vehicles and newer motorbikes, in particular BMW bikes. These have two separate circuits. One is the command circuit - that's the one you act on with your hand or foot. The second is a separate circuit controlled by an onboard computer, and that's the one which is actually connected to the brakes. As you apply the brakes, you're sending a pressure signal via the command circuit to the brake computer. It measures the amount of force you're applying, and using a servo / pump system, applies the same force to the secondary circuit to activate the brakes. If you do something stupid like trying to slam on the brakes at 100mph, the computer will realise that this would result in a skid or spin, and will not send the full pressure down the secondary circuit, instead deciding to use it's speed and ABS sensors to determine the optimal brake pressure to maintain control of the vehicle. The advantage of a dual-circuit system is that the command circuit never gets heat transferred into it because it is totally separated from the brakes themselves. The disadvantage of course is that you now have two hydraulic circuits to maintain.
BRAKE-BY-WIRE The most advanced system of brakes to date are brake-by-wire. These are a direct copy of some styles of racing brakes and are very similar to the dual-circuit hydraulic system described above, but instead of the command circuit being hydraulic, it's replaced with electronics. The brake pedal or lever is connected to a hypersensitive rheostat (measures electrical resistance). The more you push it, the greater the electrical signal sent to the brake computer. From there on, it performs just like the secondary circuit described above. The advantage to this system is that the brake pedal or lever can be placed just about anywhere you like as it no longer is encumbered by the plumbing that goes with a hydraulic circuit. To combat driver complaints of "lack of feel" in the brakes, most brake-by-wire systems have a reverse feedback loop built in. This measures the pressure being applied to the brakes on the secondary circuit, and actuates an electrical resistor in the pedal or lever assembly to provide resistance. This is needed becausethere is no physical connection to any part of the brake system at all. Like the site? The page you're reading is free, but if you like what you see and feel you've learned something, a small donation to help pay down my car loan would be appreciated. Thank you.
MECHANICAL ADVANTAGE (OR WHY YOU CAN STOP A 2-TON CAR WITH ONE FOOT). If you did any sort of physics classes when you were back in school, you might remember something called mechanical advantage. In its most basic form, mechanical advantage is the ratio of force-in to force-out in a mechanical system. Mechanical Advantage = Effort Torque/Load Torque. For example a 20kg weight 1 metre from a pivot can lift a 40kg weight 0.5m from the pivot on the other side. The effort torque and load torque calculations are to do with force in Newtons and distance from pivot point. Hence torque is measured in Newton- metres, or Nm. A Newton is the amount of force required to accelerate a mass of one kilogram by one metre per second². On Earth, where acceleration due to gravity is 9.8m/s², the force exerted upon a mass of 1kg is 9.8N (usually rounded up to 10N). Another popular notation is lbf.ft - pound-force-feet, commonly referred to as foot- pounds. 1 Newton-metre is equivalent to 0.737 foot-pounds. The diagram below shows a simple lever system on a pivot. The load torque is 200Nm, and the effort torque is also 200Nm. Mechanical advantage = effort / load, which in this case is 200 / 200, which is 1. ie. the system is balanced.
Now imagine increasing the weight on the effort side to 30kg instead of 20kg, but leaving everything else the same. The load torque is still 200Nm, but the effort torque is now 300Nm. Mechanical advantage = effort / load, which is 300 / 200, which is 1.5. Any mechanical advantage value larger than 1.0 means that the effort has the advantage. In this case, a 30kg weight which is lighter than the 40kg load, is able to lift it off the ground. If you now take your new-found / remembered knowledge about physics and look at the simple lever brake system, you'll realise how it's possible to generate enough force using your foot to stop a car or motorbike. Look at this diagram of the lever-operated cam brake.
This system has 4 levers in it. The middle two have no mechanical advantage as the levers are connected the same distance from the pivot in each case. However, look at the pedal. The values I've put in are arbitrary but they serve the purpose. On the pedal we have some amount of force 20cm from the pivot, but the other end of the lever is only 5cm from the pivot. This gives us a mechanical advantage of 4 on the brake lever (20cm / 5cm). At the other end, the lever attached to the cam is still a lever system - it's just bent. The input lever is 10cm long but the cam is only 4cm across - or 2cm to the tip from the pivot. So at the brake cam we have a mechanical advantage of 5. (10cm / 2cm). So across this entire system, we have a total mechanical advantage of 20 - 4 from the brake pedal and 5 from the lever and cam. Apply force to this little system and be amazed. The units of force used are irrelevant - they're multiplied just the same. To use easier-to-comprehend values, let's imagine that when you're braking, your foot is pushing on the brake pedal with about 60pounds of force - 27Kg. Through the brake pedal, that is amplified 4 times to 240pounds, and through the lever and cam its amplified a further 5 times from 240pounds to 1200pounds. You pushed the pedal with 60pounds of force, but the cam inside the drum brake is being forced out against the brake drum with 1200pounds of force - about 544Kg. Sweet. MECHANICAL ADVANTAGE AS APPLIED TO HYDRAULICS. Most braking systems now use hydraulics. This is a slight change in the equation but the concept of mechanical advantage still exists, this time by the use of pressure equations. Pressure = force / area. If you apply 20 Newtons of pressure to 1m², it's the same as applying 200 Newtons to 10m². Why? Because 20 Newtons of force divided by 1m² of area generates 20 Pascals of pressure. Similarly, 200N / 10m² is also 20Pa. If you now think of that in terms of a hydraulic braking system, it becomes clear how mechanical advantage works for you. Brake fluid is incompressible - it has to be. This is good because it makes calculation for hydraulic brake systems quite easy - you can eliminate the internal pressure from the equation. Split the system into two parts - input and output - the brake pedal and the brake caliper piston. For each part, Pressure = Force / Area. The Pressure is the same at all points in the system, so some basic algebra gives a simple formula: Using our previous example, we apply 60pounds (27Kg) of input force to the brake pedal. This is attached to a master piston which (for example) is 1.25cm across - ie. it has a surface area of 0.000491m² (remember your maths? area = PI x r²). At the other end of the system is the caliper piston, which for example is 2cm across - ie. it has a surface area of 0.001257m². Using our sparkly new formula, the output force from the caliper piston is 60 x (0.001257m² / 0.000491m²) Get your calculator out and that comes out to 154pounds (69.8Kg) - more than double the force at the brake pedal. The ratio of output area to input area is sometimes referred to as the area differential.
So that, my friend, is why you can stop a speeding vehicle with a single foot. WHERE TO GET BRAKE PART REPLACEMENTS. This seems like as opportune a place as any to mention that there are plenty of places on the internet and locally that will do you proud for brake parts and components if you decide to do it yourself. If you're looking for a good place to start shopping online, the brake lines, brake pads and brake rotors sections at AutoAnything seem as good a place to start as any. I mention them only because they sell the same Goodridge kits I talk about on the following page, and I was well chuffed with what that kit did to my Audi. One other thing : if you're going to be doing it yourself, a good shop manual is an absolute necessity because if there's one system on your car you don't want to be cocking up, it's the brakes. POWER BRAKES AND MASTER CYLINDERS. Power brakes (also known as power assisted brakes) are designed to use the power of the engine and/or battery to enhance your braking power. Whilst you can generate a fair amount of force using your foot, using systems from elsewhere in the car to help you apply even more force means that you get more powerful brakes as a result. The four most common types of power brakes are: vacuum suspended; air suspended; hydraulic booster, and electrohydraulic booster. Most cars use vacuum suspended units (vacuum boosters). In this type of system, when you press the brake pedal, the push rod to the master cylinder opens a vacuum control valve. This allows vacuum pressure (normally from the intake manifold) to "suck" on a diaphragm inside the vacuum assist unit. This extra vacuum suction helps you to produce more force at the pedal end of the brake system.
Hydraulic booster systems usually utilise pressure from the power steering system to augment pressure on the master brake cylinder.
Electrohydraulic booster systems use an electric motor to pressurize the hydraulic system downwind of the brake pedal which has the effect of amplifying the internal pressure in the whole system.The advantage to this system is that as long as you have battery power, you have power brakes even if the engine fails. With vacuum-assist brakes, no engine means no assistance.
If you're curious about how power brakes work, go out to your car and with the engine off, step on the brakes. They'll have a slightly solid, almost wooden feel to them. Turn the engine on and do it again and you'll notice a lot less back-pressure on the pedal. This is the power assist which is making it easier for you to depress the pedal. THE COMPONENTS OF A MASTER CYLINDER.
Brake master cylinders are complicated affairs involving finely manufactured parts, minute tolerances, springs, o-rings and rubber seals. The diagram here is a simplified representation of a dual-circuit master brake cylinder. When you step on the brake, its connected to the main plunger (on the right side of this image). As this is pushed into the master cylinder it acts on the components inside. The rear plunger (in blue) is the first one to start moving. As it moves forward, brake fluid from the reservoir is sucked in through the fluid intake and return port. At the same time, fluid is sucked in through the equalisation port. As the second circuit rear seal passes the intake and return port (about 1.5mm after the plunger starts moving), it creates a fixed volume of fluid between the rear and front plungers. The more you step on the brake pedal, the more this fluid is now forced out into the second brake circuit to apply those brakes. At the same time, the pressure building up in this area overcomes the strength of the first circuit return spring and the front plunger (red) begins to move too. As with the rear plunger, it too sucks fluid from the reservoir until the first circuit rear seal passes the fluid intake and return port (again about 1.5mm), trapping fluid between it and the front of the master cylinder. This fluid is then forced out into the first brake circuit, applying those brakes. When you take your foot off the brakes, the return springs push the plungers back into their neutral position. Fluid returns to the brake fluid reservoir and the system goes back to an unpressurised state. One last thing about brake master cylinders: they used to cost an absolute bomb to replace. Historically if your 20 year old beater developed a leak, it was probably cheaper to buy another used car than to replace the master cylinder. Nowadays not so much. The internet changed all that in the mid to late 90's with online parts stores, which drove prices right down. Now you can pick up new master cylinders for $200 or so. That's a price break which is cheap enough that it's silly to get your leaking one remanufactured when you can just grab a new one. CROSS-LINKED BRAKES (OR WHY THERE ARE TWO BRAKE CIRCUITS). In the rendering of the master brake cylinder above, you'll see there are two plungers and two brake circuits. This is the most common design for cars today. It's a form of redundancy in the brake system. The idea is that only two brakes, one front and one rear, are on either of the brake circuits. For four brakes, you therefore need two circuits. But why? Well imagine one of your brake lines springs a leak - for the sake of argument, the front-left brake. If all four brakes were on a single circuit, when the master cylinder began to pressurise the brake system, fluid would spurt out of the broken line and pressure would never build up. In turn, that means none of the brakes would ever come on and you'll sail merrily into the back of the vehicle in front of you.
Imagine the same scenario with two circuits. As the first circuit pressurises the front-left and rear-right brakes, fluid spurts out of the broken line and those brakes are never applied. However because the master cylinder is also pressurising a separate second circuit connected to the front-right and rear-left wheels, those brakes do apply and you've still got braking force. Sure, it's reduced, but it's a hell of a lot better than no brakes at all. Because of the front-left to rear-right and front-right to rear-left linking of the brake circuits, this type of system is known as cross-linked brakes. The rendering here shows an example arrangement of cross-linked brakes.
A WORD ABOUT HANDBRAKES. It's worth spending a moment here to talk about handbrakes. Or parking brakes, e- brakes or emergency brakes depending on where you come from. Whilst they're good for doing handbrake turns, they're not especially effective at actually slowing you down. They will - don't get me wrong - but you won't be seeing any stellar performance out of them so the term 'emergency brake' is a bit of a misnomer. So why is this? Well, handbrakes are cable-actuated for a start so the amount of power they have is wholly dependent on the amount of tug you have in your arm. There's no hydraulic system to help you out. Apart from that, they only work on the rear wheels, so you're not getting four-wheel braking. On drum-brakes, the handbrake is connected to a small lever that pivots against the end of one of the brake actuating pistons. When you pull the handbrake, the lever gets pulled and the brake shoes are pressed out against the inside of the drum. On disc brakes, the handbrake normally works a second set of brake pads in the rear caliper. They're little spots, about the size of a grown man's thumbprint and they're clamped mechanically against the brake rotor. These pads never need changing because they're normally only used at standstill so generally don't wear much. Their small size is the other reason you shouldn't expect stellar stopping performance if you yank on the handbrake. That being said, there are derivatives of disc-based handbrakes that use a mechanical arm to press the main brake pads against the rotor although these are less common as far as I know. WHEN TO USE HANDBRAKES Typically you ought to use your handbrake whenever you're stopped somewhere, be it parked, on a hill or waiting at traffic lights. The reason is simple : if you're parked or stopped, you generally don't want the car to run off without you. At traffic lights, it's an accident minimisation function as much as anything. If you're sitting there with your foot on the brake and someone drives into the back of you, the impact will cause you to take your foot off the brake and you'll go sailing into the car in front, causing more accidents. If you have the handbrake on in the same scenario, your car will largely stay put (apart from the initial shove across the ground as the energy from the impact is dissapated through your tyres). Of course there are personal habits and mechanical complications to contend with here. For example in a car with an automatic gearbox, it's force of habit to just use the footbrake. Even so, you should still use the handbrake when you're parked, especially on an incline. The 'park' setting on automatic gearboxes isn't sufficient to hold a car on a hill, and apart from that, it puts incredible strain on the transmission and clutch system if you let the whole weight of the car transfer into the transmission to try to keep it from moving. In some American cars, the handbrake isn't a handbrake at all, it's a second footbrake on the far left side of the footwell, which is basically totally useless because it's a pain to put on and even more of a pain to get off because it's a one-way ratchet system (you have to force the pedal all the way down to get it to release). Then there's the ignorance factor. When I went to my new owners orientation evening after buying a Subaru in America, one lady asked what the parking brake was for. (Apparently the name wasn't obvious enough). The dealer representative told her it was a relic of days gone by, not to be used, and he didn't understand why manufacturers even put them in cars any more! WHEN NOT TO USE HANDBRAKES The first and most obvious answer to this is : when you're going at any speed. If you yank on the handbrake at any speed much over 30km/h, the back end of your car will start to slide. Great for stunts and tricks, not so great if you're trying to stop in 5 lanes of crowded motorway traffic. The other time you should not use your handbrake is in post-snow, freezing conditions. With the salt and grit that gets put down on the roads, you'll be driving through a salty, snowy slush and it will be spraying all over the underside of your car. If you park and put the handbrake on, you risk it binding on by freezing. Why? Well handbrake cables are almost always exposed to the elements at some point under your car. If you put the handbrake on and the cable is covered in slush, as it freezes again it will lock the handbrake on. There's no solution to this other than waiting for the weather to warm up. Well, not unless you fancy a crack at the Darwin Awards, because some people have tried using blowtorches to thaw the ice, not understanding that they were working right underneath the petrol tank. So here's a tip : don't. If you need to park in those types of conditions, try to find level ground and leave your automatic gearbox in "p" or your manual gearbox either in first or reverse gears. REGIONAL VARIATIONS One last thing to know about handbrakes : for some reason, from-the-factory settings on handbrakes vary largely with region. In Europe for example, the handbrake is easily capable of exerting enough friction to prevent the engine from being able to move the car from standstill. In America, it's not uncommon to see handbrakes adjusted to lightly that even when fully on, you can just drive off. The only way you'll notice is the handbrake light on the dash, the lack of performance, or the smell of burning as your rear brakes burn off. ANTI LOCK BRAKING SYSTEMS - ABS Stop without skidding, and maintain control of the vehicle. That's the premise of ABS. It was first introduced in the 1980's and has been undergoing constant refinement ever since. The system is typically comprised of 4 ABS rings, 4 sensors, an ABS computer and a number of pressure-management circuits in the brake lines. The ABS rings are attached either to the wheels, or more often, to the brake discs. They look like a notched ring - see the image to the right.
The sensors are magnetic field sensors which are held very close to the ABS rings and can detect the slight change in magnetic field as the teeth on the ring pass them. The pulsing field tells the ABS computer that the wheels are spinning, and how fast they're spinning. When you brake, the wheel rotation starts to slow down. The ABS computer "listens" to the input from the sensors and can detect if one wheel is slowing down much quicker than the others - the precursor to the wheel locking up. (This all happens in milliseconds, by the way). When the computer detects this condition, a pressure regulator in the brake circuit interrupts the pressure in the brake lines by momentarily reducing it so that the brakes release just enough to give the wheels a chance to keep spinning rather than locking up. The computer then instructs the regulator to re-apply full pressure and again measures the wheel rotation. This on/off/measure cycle happens around 15 to 30 times a second. If the ABS kicks in, you'll feel it through the brake pedal as a vibration because the pulsing in the brake circuit affects all the components. NEWER GENERATION ABS SYSTEMS As technology marches on, so does the control / feedback system used in ABS. It used to be the case that any single wheel approaching lockup would cause the ABS system to pulse the brake pressure for all the wheels. With the latest vehicles, the ABS computer is connected to 4 pressure regulators instead of just the one. This means it can selectively apply pulsed braking only to the wheel(s) that need it. So if three of the tyres are gripping well, but the front-left is beginning to skid, the ABS can unlock the front-left brake and pulse it to try to regain grip. It's called three- or four-circuit ABS and it's all very James Bond. When hooked up to the traction control system, this type of multi-circuit ABS can also be used to influence the overall traction of a car in extreme maneuvers, such as helping to prevent rollover and inside-wheel-lifting. ABS AND SKID CONTROL So how to talk about the biggest misconception about ABS - that it will make you come to a stop more quickly? This is a prickly subject to talk about. In one camp you have drivers like me who just can't stomach the idea of a computer breaking the physical connection between my right foot and the brake system. Whilst in the other camp you have people who believe that ABS is the best thing since sliced bread. It's these people in the second camp who have the all-out belief that ABS will help you stop faster, and in certain conditions, this is true. On a wet or greasy road surface where the traction is severely reduced, an ABS system can pulse the brakes and prevent lockup much better than a human can. But why? The whole point of brakes is to slow you down. To do that they rely on friction in two places - between the brake pads and the rotors, and between the tyres and road surface. If one of those factors is taken out of the equation, the brakes become useless. The most typical situation is that a driver will panic-react to something and step on the brakes with as much power as they can muster. The brake system amplifies this power, grabs hold of the brake rotors and the wheels stop turning almost instantly. This causes the tyres to now skid across the road surface, and as they do so, they become subject to dynamic attrition. In other words, if a tyre is rotating and gripping the road, the "stick" factor is much higher than if the wheel is locked and skating across the same surface. So that's what ABS does - in an emergency, it ensures that the wheels don't lock up but instead keep spinning so that the tyres maintain grip with the road. (That's where ABS gets its name - Anti-Lock Brakes.) This is where the real benefit of ABS comes into play. If you're going to attempt to avoid an accident, the best thing to do is to try to steer around it. If your tyres are skidding on the road surface, you can point your wheels pretty much wherever you want because the actual direction you end up going will have nothing to do with the wheels and everything to do with the direction you weretravelling, combined with the camber of the road. Once the tyres lose grip, all bets are off. With ABS, if those wheels keep turning and the tyres keep gripping, then when you ham-fistedly grab the steering and yank it to one side, the car will still turn and you might be able to avoid the accident. So that's the true essence of ABS - to maintain control over the direction of the car. SO WHY THE NEGATIVITY, CHRIS? My bone of contention with ABS is not so much to do with the technology as the placebo effect is has on drivers. ABS is widely misunderstood and if you ask most drivers, they'll tell you that ABS helps them to stop more quickly, and as I illustrated above, in certain conditions this is true. But even the most well-trained driver is going to be subject to panic in an emergency, and more often than not, will lock their arms on the steering wheel bracing for the coming impact. Once you do this, you're no longer steering so the ABS is trying to give you control over your car but you're not taking advantage of it. Given that this is the most natural human instinct, people accept this as "the way of crashes" but somehow believe that if they have ABS, they'll be able to stop before they get to the point of impact, and that's simply not true. I believe too many people think ABS gives them a license to drive faster, because they mistakenly believe that it will get them out of any situation. It's yet another technical placebo that has been put into vehicles which is making the standard of driving worse. The more gadgets and "driver aids" that get put into a car, the worse the drivers become because they live in a rose- spectacled world where they believe that it's the car's responsibility to get them out of any sticky situation that might arise. It bothers me so much I have a "rant" page dedicated to it here :Nanny Cars. POLITICAL CORRECTNESS AND THE PUSH FOR ABS IN EVERY VEHICLE It's a widely perpetrated myth that speeding is the cause of most accidents, so it follows that if you can develop a method of helping drivers to bring their vehicles to a stop in a more controlled fashion, you'll help to reduce the number of accidents. Good idea, but it doesn't have a lot of substance to it. If you check my page with studies on the facts vs. the fiction of speeding, you'll see that only 4% of all accidents are caused by loss of control of the vehicle with excessive speed as the primary contributing factor. So ABS wasn't really designed for that - it's difficult to reduce the incidence of the already lowest cause of motoring-related accidents. In truth, distracted drivers (like I mentioned above, driving in their cosetted mobile living rooms), their actual ability to drive properly (training and advanced driver courses) and their ability to have some form of spatial awareness are much bigger factors than speed itself and none of those can be overcome by clever braking systems. Shouldn't we be pushing for more driver training programs to attempt to treat the real cause of the accidents rather than simply putting a bandage on the result? So what about the emotive issue of pedestrian accidents? What if you, the driver, could stop quicker? It's a staggering fact that 84% of vehicle-pedestrian accidents are actually the pedestrian's fault and in most of those cases, even if you could have stopped on a dime, the accident would not have been prevented. Seriously. Read the the facts vs. the fiction of speeding page - you'll be astonished. I'm not condoning running over pedestrians - that would be stupid. I know first-hand what it's like - I had one of those 84% jog out in front of me using his cellphone when I was riding my motorcycle some years ago. I hit him square in the back despite being hard on the brakes, and threw him a good 10 metres down the road. He survived with some scrapes and bruises but I still think about it to this day. I can't begin to imagine what it would have been like if the stupid bugger had actually died. ABS IN SNOW AND ICE, AND ON GRAVEL
Ah yes. The subject of a good 75% of the emails I get about ABS. The two camps for this argument are split almost exactly 50/50. In one camp, those like me who from experience would rather have their tyres lock up in deep snow to give me at least a fleeting chance of having them dig through the snow to find some road. Those who have anecdotal evidence that ABS is total crap in snow and ice. Whilst in the other camp, those who again believe ABS will somehow magically stop them from crashing in the same conditions. Those who have similar anecdotal evidence disproving all those in the first camp. ABS by its very nature is designed to stop the wheels from skidding by allowing them to keep turning. On deep packed snow and ice, that's exactly what they're going to do - skid, so ABS effectively removes a considerable amount of your braking in an emergency in these conditions. It's why some cars have ABS disable systems for snow and ice, and it's why ice racers yank the fuse to the ABS system before they even get in a car to race. The ABS Education Alliance, a group aiming to help educate drivers on how ABS will best benefit them, has this to say on the subject: Even in fresh snow conditions, you gain the advantages of better steerability and stability with four-wheel ABS than with a conventional system that could result in locked wheels. In exchange for an increased stopping distance, the vehicle will remain stable and maintain full steering since the wheels won't be locked. The gain in stability makes the increase in stopping distances an acceptable compromise for most drivers. So the short answer to this debate is that ABS is worse in snow and ice for overall stopping distance, but better for controlability. THE HIDDEN GREMLIN OF ABS - WHAT THEY DON'T ADVERTISE. If you look at the statistics for crashes, a large percentage of them are "fender benders" - low-speed impacts that only do a little damage and so slow that the vehicle occupants are in no danger; normally about 10mph. I'll give you one guess what the typical "minimum activation speed" is for ABS. That's right. On a lot of vehicles, the ABS is useless much below about 10mph. Seriously. Try it yourself. Find an empty road on a slight downhill grade - even better if its on a dewy morning. Run your ABS-equipped car up to about 10mph and jam on the brakes as hard as you can. The car will skid to a stop and the ABS system will remain totally silent. AFTERMARKET ABS SYSTEMS To the best of my knowledge, there's no such thing. A few years back a couple of companies tried to market what they called ABS systems that could be retrofitted to any vehicle. The product was a cylinder with a pressure-relief valve in it. The idea was that you inserted this system into the brake circuit somewhere. When you stomped on the brakes - symptomatic of locking up the wheels - the pressure relief valve opened and bled off some brake fluid into the cylinder, thus lowering the braking pressure being sent to the wheels. The idea was to take the "spike" off the initial push of the brake pedal so it wasn't ABS at all. The whole idea of putting something like this into a brake circuit makes me shudder - I wouldn't want to be the person trying to get their insurance and medical claims through after an accident when the investigators found one of these contraptions in their brake line! A FINAL THOUGHT ON ABS Consider this: if you're in an accident and your ABS works perfectly, you'll leave no skidmarks on the road surface. An inspection of the car will show the brakes and ABS system are working perfectly but the absence of skidmarks could lead the police accident scene investigator to believe you didn't brake at all. That in turn could lead to you being the "at fault" driver with all the consequences that involves. Think about it. This exact scenario happens many times every day. Amongst all those ABS-related emails I get, at least one a week is telling me about someone who's had this problem..... REMEMBER : ABS ATTEMPTS TO ENSURE THAT YOUR CAR STOPS IN THE SHORTEST DISTANCE POSSIBLE FOR MOST ROAD SURFACES. IT IS NOT A SUBSTITUTE FOR YOU, THE DRIVER, PAYING ATTENTION TO THE ROAD AND YOUR DRIVING. BRAKE-ASSIST AND COLLISION WARNING SYSTEMS Picture credit: Volvo By 2006, brake-assist and accident warning systems were starting to find their way into consumer cars. I for one just don't like the idea. The manufacturers are reinforcing the misconception that the driver is no longer responsible for their actions. Volvo's collision warning system (CWS), for example, constantly monitors your speed and uses a radar with a 15° forward field of view to determine the distance to any object in front of you. If the distance begins to shrink but you don't slow down, the system sounds a buzzer and flashes a bright red light in a heads-up display to alert you. The brake pads are automatically placed against the discs and when the driver finally does use the brakes, the system monitors the pedal pressure. If the pressure is determined to be too light, the braking power is amplified by the system. It's a great idea, but the TV commercials for this system need some serious attention. Volvo's commercials actually show a woman driving a Volvo, arranging papers on her passenger seat and talking on a cellphone. When the collision warning system activates and she looks up, bemused, then applies the brakes to avoid running into a truck in front of her - a truck that she would have seen and presumably slowed down for had she been paying attention. I know it's not meant to be taken this way, but that Volvo commercial actually appears to be promoting distracted driving - Volvo will attempt to save you from your own ineptitude because apparently it's just too inconvenient now to be paying attention to the road ahead. Rather than train drivers to understand that they need to be responsible for their actions, that they need to be alert to their surroundings and that they need to pay attention when they're driving, collision warning systems essentially attempt to treat the symptoms rather than trying to cure the problem itself. Brake-assist and auto-brakes go one step further. In some high end vehicle now (top end BMWs and Mercedes' for example), the collision-detection system is linked into the brakes like it is with the Volvo system, but it's also been given the flexibility to do all the braking for you. Adaptive cruise control, for example, will control the throttle just like a normal cruise control system, but will also apply the brakes if it determines that you're getting too close to the vehicle in front. Full auto-brakes will actually stop the car for you if you fail to respond. All these systems work in essentially the same way - they monitor the brake use and distance to the vehicle in front. If the computer thinks you're not braking hard enough, it will assist you. These systems are all very clever but they tread the thin ethical line. Just because engineers can make their vehicles do this doesn't mean they should. Consider this: with in-vehicle monitoring and tracking systems like OnStar, and the impending satellite- tracking systems for road tolling, it's not too hard to imagine all those systems chained together in such a way that the vehicle will literally prevent you from speeding by limiting the throttle availability and controlling the brakes. If you really want to be driven like that in a vehicle over which you have no control at all, take the bus.
Now don't misunderstand me here - I think a lot of what Volvo do in vehicle safety is a good idea - the transparent A-pillars, the blind-spot assist and things like that - they all go towards eliminating problems inherent with the design of cars. But I believe putting systems into a car that attempt to compensate for the ineptitude of the person behind the wheel is a mistake. But that's just my opinion.
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OTHER BRAKE TECHNOLOGIES There are other brake technologies that are becoming available in vehicles now, and a lot of them are gathered together in the 2006 / 2007 BMW models. They're the rolling embodiment of clever brake engineers just showing off. Three of the more notable features are: . Brake Drying. The X3 has rain-sensing windscreen wipers. When they sense rain, they also send information to the onboard computer. In turn, it goes into a cycle of occasionally bringing the pads into light contact with the brake rotors. This generates enough friction to eliminate any film of water that might be on the surface of the rotors, but not enough that it slows the car down or is even detectable by the driver. . Brake Stand-by. This is a pre-emptive system that attempts to detect when sharp braking is about to happen. Potentiometers attached the accelerator can detect when the driver takes their foot off it very quickly. That would normally be followed by the brake being applied very quickly. When the onboard computer senses this condition, it moves the brake pads right up to the rotors using the same mechanism that the brake drying system uses. Ultimately, if the driver does jump on the brakes, they're ready to work the millisecond the driver's foot touches the pedal. It may not sound much but that tiny difference in distance moved, translates into a saving in time between putting your foot on the brake and the car actually slowing down. That in turn translates into forward distance - or less of it. . Brake Fade Compensation. Right up at the top of the page I explained what brake fade was. If the brake rotor temperature begins to rise, this system increases the hydraulic pressure used to press the pads against the rotors without requiring any more pressure on the brake pedal. I'm not sure if this system has a warning light or not, but it should otherwise drivers could end up driving on horribly faded brakes without realising it, and eventually, even the extra hydraulic pressure isn't going to help. All the above devices fall into that ethical grey area again, but unlike the brake-assist and collision-detection systems outlined earlier, these three brake technologies don't actually attempt to compensate for any wrongdoing on the driver's behalf. They simply help prepare the car for when the driver chooses to use the brakes. From that point of view, I would regard these as better technologies than those which go the whole hog and interfere with your driving. BRAKE HOSES - NOT JUST RUBBER. Obviously with all the pressure in your brake system, the last thing you need is for the brake lines themselves to deform and flex. If they do, you lose brake pressure, and thus lose braking. Steel brake lines are no problem, but for the flexible areas of the brake lines, you need hoses. Brake hoses come in two basic flavours. RUBBER HOSES. Ah the humble rubber hose. Only on your brake lines, not so humble. I don't recommend this but if you were to get under your car and cut one of your hoses in half, you'd notice a couple of things. First, it's amazing how quick all the brake fluid that spills out will stain your clothes and literally eat the paint off your car right in front of you. But second, and more importantly, the hose itself is actually made of three parts. The inner liner is a corrosion and brake-fluid resistant compound designed (normally PTFE / Teflon® based) purely to keep the brake fluid in. Around the outside of that, there's a steel webbed mesh. This is what gives the brake hose its strength and stops it from bulging and deforming. And around the outside of that there's a slightly thicker rubber coating, which is there to weatherproof the steel mesh. The three layers together give strength, flexibility and durability. STEEL-BRAIDED HOSES.
Steel-braided hoses are a slightly different design. They only really have two components - the inner hose which carries the brake fluid and is lined with a PTFE compound, and the outer steel braid which contains and flexing or bulging. Steel- braided lines resist bulging a lot better which is why a lot of aftermarket tuners opt to put them on their vehicles. One downside is that the steel braiding itself is totally merciless and if it finds something to rub against in the vehicle, it will rub right through it, even if it's an alloy. For that reason, a lot of braided brake hose manufacturers put a third layer - a thin transparent rubber sheath around the outside simply to keep everything in check and prevent scuffing and rubbing. I upgraded the lines on my Audi when I still owned it and put Goodridge steel braided hoses on. For a 15 year old car it did make a difference to the feel of the brake pedal. It didn't bring it up to modern standards, but it was better than the flexible, bendy rubber hoses that were on it from the factory. BRAKE FLUIDS.
As mentioned elsewhere on the page, brake fluid does not compress. It's a good job too - if you put your foot on the brake pedal and it went all the way to the floor, you'd be worried. But that's exactly what can happen if you disregard the "health" of your brake fluid. Brake fluid is hygroscopic - that means it attracts and soaks up water. This is why it comes in sealed containers when you buy it, and why when the crazy guy four doors down offers you some of the 15 gallons of brake fluid he's had in his garage since the war, you should turn him down. The problem with it being hygroscopic is that if it does start to take on water, Bad Things can happen. Pull up a chair and allow me to explain. Your typical DOT 4 brake fluid (see later for DOT ratings) boils at about 446°F (230°C). Water boils at 212°F (100°C). Imagine your brakes are getting hot because of a long downhill stretch. Whilst the brake fluid is quite OK, the temperature of the brake components might get up over the boiling point of water. If that happens, the water boils out of the brake fluid and forms steam - a compressible gas. Next time you put your foot on the brake, rather than braking, all the pressure in the brake system is taken up with compressing the steam. Your brakes go out, you don't stop. Getting a little more complex, the boiling point of a liquid goes up with its pressure (Physics 101). So when you step on the brake, the boiling point of the brake fluid might actually go up to 500°F (260°C) and the boiling point of the water content might raise up to 250°F (121°C). This is great, you might think, because now the boiling point is higher than the temperature of the brake fluid. At least it is until you take your foot off the brake again. Now the pressure in the system returns to normal, the boiling points revert to normal and instantly the water boils off into steam again. The symptoms are slightly different now. Under this scenario, the brakes work the first one or two times, but on the third or fourth press, they stop working because now the temperature and pressures have conspired to boil the water. The worst possible scenario is brake-fade (see right at the top) combined with air in the system. If this has happened to you, then you're likely reading this page from beyond the grave, because in most accidents where weak brakes become no brakes, there aren't any survivors. D.O.T RATINGS All brake fluids are DOT rated. Your owners handbook for your car or motorbike probably tells you to use DOT3 or DOT4 from a sealed container. The DOT ratings are a set of minimum standards the fluid must adhere to in order to get the rating, and thus work in your braking system. The following table shows the various properties of DOT ratings. Remember that the values here are the minimum values. Most manufacturers make sure their product far exceeds minimum ratings. Boiling DOT DOT DOT 5 (silicone- DOT 5.1 (non-silicone Point 3 4 based) based) Dry 401°F 446°F 500°F 500°F Wet 284°F 311°F 365°F 365°F The "dry" and "wet" boiling points in the table above are for brake fluid which is fresh from the bottle (dry) and which has a 10% water content (wet). A DOT study in 2000 discovered that on average, the brake fluid in a vehicle absorbs about 2% water every 12 months. The two types of brake fluids shown in the table are DOT3/DOT4/DOT5.1 which are glycol (Polyalkylene Glycol Ether) based, and DOT5 which is silicone based. DOT3 and DOT4 fluids are interchangeable* - the only real difference is their boiling point. Theoretically you could interchange DOT4 and DOT5.1 fluids too but I wouldn't recommend it. DOT3/4/5.1 and DOT5 fluids cannot be mixed or interchanged under any circumstances. They mix like oil and water (ie. they don't) and the silicon based fluids can destroy the seals in brake systems which rely on the moisturiser additives that are present in DOT3/4/5.1 fluids. Other things you ought to know about silicone based fluids: - they are resistant to absorbing water, which is why their wet boiling points are so high. Problem is that any water content eventually pools in the low spots of the brake system and causes rust. - they don't strip paint. - they are not compatible with most ABS system because they doesn't lubricate the ABS pump like a glycol based fluid. - putting this fluid in systems which have had DOT3/4 fluid in will cause the seals in the caliper and master cylinders to malfunction. Which means they need replacing. Which is expensive.
Oh, and don't ask me why DOT5.1 is glycol and DOT5 is silicon based. It doesn't make and sense to me either.
* There has been some discussion as to the use of DOT4 fluid in Toyotas that recommend DOT3 fluid - apparently something in the Toyota braking system doesn't play well with DOT4 fluid, particularly the master brake cylinder seals. The discussion about this can be found in the archives at the UK Pruis yahoo group. BRAKE WARNING LIGHTS
Most cars nowadays have a brake warning light on the dash. Its purpose is to alert you that something is wrong in the braking system somewhere. If it comes on, check your owner's manual to find out its meaning. Unlike the single-purpose ABS warning light, the brake warning light doesn't have a standard meaning; it could be used for multiple purposes. For example, the same light may be used to show that the hand brake (parking brake for the Americans amongst you) is on. If that's the case and you're driving, you ought to have noticed the smell of burning brake dust by now. The light can also indicate that the fluid in the master cylinder is low. Each manufacturer has a different use and standard for this light. Which is nice. Because it would be such a drag if the same indicator meant the same thing in every vehicle.
If you've got an ABS-equipped car, you also have a second light - the ABS light. If it comes on, get it seen to as soon as possible. It means the ABS computer has diagnosed that something is amiss in the system. It could be something as simple as dirt in one of the sensors, or something as costly as an entire ABS unit replacement. Either way, if that light is on, then you, my friend, have got 1970's brakes. It's important to note that this light normally comes on when you start the car and then switches off a few seconds later. If it stays on, blinks, throbs, flashes or in any other way draws your attention to itself, take note. It's not doing it just to please itself.
If you see this light on your dashboard, then congratulations - you're flying the service module on an Apollo mission. The bad news is that you've got a current drain somewhere and your main batteries are critically low. Either way, drop me a line and let me know how you snagged a seat on a spaceflight - I'm dying to know. AND FINALLY....LED REPLACEMENT BULBS
You might have seen websites and automotive shops stocking LED replacement bulbs for cars and motorbikes. The most basic replacements look like those on the right - a cluster of 19 or 24 LEDS (light emitting diodes) in a housing with a regular push-fit or bayonet plug on the back. The idea is that if you want brighter lights, you can replace your tail or turn lights with these LED replacements. There is a gotcha though that the manufacturers often hide in the smallest of small print. A lot of vehicles (cars and motorbikes) have onboard diagnostics which include a light check. Some of these use resistance to figure out if a bulb has blown. LED clusters have a radically different resistance to a filament bulb and its possible that when you replace your bulbs with LED versions, your car will continuously tell you that one or more bulbs is burned out. Getting one step more severe, if you use LED turn bulbs, your indicators could flash quicker or slower than you're used to (indicator circuits use the natural resistance of the bulbs in conjunction with the relay to dictate the flash speed). The worst case scenario though is ABS; some motorbikes have very tightly regulated voltages in their ABS systems and taking the filament bulb out of the brake light to replace it with an LED bulb can cause ABS errors and theoretically, an ABS shutdown. Granted thats worst-case scenario, but it is a possibility. The way around all these electrical load problems is to add resistance or ballast to the bulb replacement, and this is becoming more common now. Essentially, resistors are added in-line with the LEDs to provide the same sort of resistance to current flow that an incandescent bulb would, thus making the retrofit kits far more compatible with existing car or motorbike electrical systems. CycoActive make kits like this for motorbikes now. You can see an example on the left here which shows the LED unit as a complete replacement for the tail unit on a bike, with a bayonet connector to fit into the old socket. The blue items are the ballast resistors designed to induce sufficient load in the electrical system for the diagnostics to register the unit as a regular lightbulb. THE TRANSMISSION BIBLE
TRANSMISSION, OR GEARBOX? That question depends on which side of the Atlantic you're on. To the Europeans, it's a gearbox. To the Americans, it's a transmission. Although to be truthful, the transmission is the entire assembly that sits behind the flywheel and clutch - the gearbox is really a subset of the transmission if you want to split hairs. Either way, this page aims to deal with the whole idea of getting the power from your engine to the ground in order to move your car (or bike) forwards. MANUAL GEARBOXES - WHAT, WHY AND HOW? From the Fuel & Engine Bible you know that the pistons drive the main crank in your engine so that it spins. Idling, it spins around 900rpm. At speed it can be anything up to 7,500rpm. You can't simply connect a set of wheels to the end of the crank because the speed is too high and too variable, and you'd need to stall the engine every time you wanted to stand still. Instead you need to reduce the revolutions of the crank down to a usable value. This is known as gearing down - the mechanical process of using interlocking gears to reduce the number of revolutions of something that is spinning. A QUICK PRIMER ON HOW GEARS WORK In this case I'm talking about gears meaning 'toothed wheel' as oppose to gears as in 'my car has 5 gears'. A gear (or cog, or sprocket) in its most basic form is a flat circular object that has teeth cut into the edge of it. The most basic type of gear is called a spur gear, and it has straight-cut teeth, where the angle of the teeth is parallel to the axis of the gear. Wider gears and those that are cut for smoother meshing are often cut with the teeth at an angle, and these are called helical gears. Because of the angle of cut, helical gear teeth have a much more gradual engagement with each other, and as such they operate a lot more smoothly and quietly than spur gears. Gearboxes for cars and motorbikes almost always use helical gears because of this. A side effect of helical gears is that if the teeth are cut at the correct angle - 45 degrees - a pair of gears can be meshed together perpendicular to each other. This is a useful method of changing the direction of movement or thrust in a mechanical system. Another method would be to use bevel gears.
The number of teeth cut into the edge of a gear determines its scalar relative to other gears in a mechanical system. For example, if you mesh together a 20-tooth gear and a 10-tooth gear, then drive the 20-tooth gear for one rotation, it will cause the 10-tooth gear to turn twice. Gear ratios are calculated by divinding the number of teeth on the output gear by the number of teeth on the input gear. So the gear ratio here is output/input, 10/20 = 1/2 = 1:2. Gear ratios are often simplified to represent the number of times the output gear has to turn once. In this example, 1:2 is 0.5:1 - "point fiveto one". Meaning the input gear has to spin half a revolution to drive the output gear once. This is known as gearingup.
Gearing down is exactly the same only the input gear is now the one with the least number of teeth. In this case, driving the 10-tooth gear as the input gear gives us output/input of 20/10 = 2/1 = 2:1 - "two to one". Meaning the input gear has to spin twice to drive the output gear once.
By meshing many gears together of different sizes, you can create a mechanical system to gear up or gear down the number of rotations very quickly. As a final example, imagine an input gear with 10 teeth, a secondary gear with 20 teeth and a final gear with 30 teeth. From the input gear to the secondary gear, the ratio is 20/10 = 2:1. From the second gear to the final gear, the ratio is 30/20 = 1.5:1. The total gear ratio for this system is (2 * 1.5):1, or 3:1. ie. to turn the output gear once, the input gear has to turn three times. This also neatly shows how you can do the calculation and miss the middle gear ratios - ultimately you need the ratio of input to output. In this example, the final output is 30 and the original input is 10. 30/10 = 3/1 = 3:1. Collections of helical gears in a gearbox are what give the gearing down of the speed of the engine crank to the final speed of the output shaft from the gearbox. The table below shows some example gear ratios for a 5-speed manual gearbox (in this case a Subaru Impreza). RPM of gearbox output shaft Gear Ratio when the engine is at 3000rpm 1st 3.166:1 947 2nd 1.882:1 1594 3rd 1.296:1 2314 4th 0.972:1 3086 5th 0.738:1 4065
Final drive - calculating speed from gearbox ratios. It's important to note that in almost all vehicles there is also a final reduction gear. This is also called a final drive or a rear- or front-axle gear reduction and it's done in the differential with a small pinion gear and a large ring gear (see the section on differentials lower down the page). In the Subaru example above, it is 4.444:1. This is the final reduction from the output shaft of the gearbox to the driveshafts coming out of the differential to the wheels. So using the example above, in 5th gear, at 3000rpm, the gearbox output shaft spins at 4065rpm. This goes through a 4.444:1 reduction in the differential to give a wheel driveshaft rotation of 914rpm. For a Subaru, assume a wheel and tyre combo of 205/55R16 giving a circumference of 1.985m or 6.512ft (seeThe Wheel & Tyre Bible). Each minute, the wheel spins 914 times meaning it moves the car (914 x 6.512ft) = 5951ft along the ground, or 1.127 miles. In an hour, that's (60minutes x 1.127miles) = 67.62. In other words, knowing the gearbox ratios and tyre sizes, you can figure out that at 3000rpm, this car will be doing 67mph in 5th gear. MAKING THOSE GEARS WORK TOGETHER TO MAKE A GEARBOX If you look at the image here you'll see a the internals of a generic gearbox. You can see the helical gears meshing with each other. The lower shaft in this image is called the layshaft - it's the one connected to the clutch - the one driven directly by the engine. The output shaft is the upper shaft in this image. To the uneducated eye, this looks like a mechanical nightmare. Once you get done with this section, you'll be able to look at this image and say with some authority, "Ah yes, that's a 5-speed gearbox". So how can you tell? Well look at the output shaft. You can see 5 helical gears and 3 sets of selector forks. At the most basic level, that tells you this is a 5-speed box (note that my example has no reverse gear) But how does it work? It's actually a lot simpler than most people think although after reading the following explanation you might be in need of a brain massage. With the clutch engaged (see the section on clutches below), the layshaft is always turning. All the helical gears on the layshaft are permanently attached to it so they all turn at the same rate. They mesh with a series of gears on the output shaft that are mounted on sliprings so they actually spin around the output shaft without turning it. Look closely at the selector forks; you'll see they are slipped around a series of collars with teeth on the inside. Those are the dog gears and the teeth are the dog teeth. The dog gears are mounted to the output shaft on a splined section which allows them to slide back and forth. When you move the gear stick, a series of mechanical pushrod connections move the various selector forks, sliding the dog gears back and forth. In the image to the left, I've rendered a close-up of the area between third and fourth gear. When the gearstick is moved to select fourth gear, the selector fork slides backwards. This slides the dog gear backwards on the splined shaft and the dog teeth engage with the teeth on the front of the helical fourth gear. This locks it to the dog gear which itself is locked to the output shaft with the splines. When the clutch is let out and the engine drives the layhshaft, all the gears turn as before but now the second helical gear is locked to the output shaft and voila - fourth gear.
Grinding gears. In the above example, to engage fourth gear, the dog gear is disengaged from the third helical gear and slides backwards to engage with the fourth helical gear. This is why you need a clutch and it's also the cause of the grinding noise from a gearbox when someone is cocking up their gearchange. The common misconception is that this grinding noise is the teeth of the gears grinding together. It isn't. Rather it's the sound of the teeth on the dog gears skipping across the dog teeth of the helical output gears and not managing to engage properly. This typically happens when the clutch is let out too soon and the gearbox is attempting to engage at the same time as it's trying to drive. Doesn't work. In older cars, it's the reason you needed to do something called double-clutching. Double-clutching, or double-de-clutching (I've heard it called both) was a process that needed to happen on older gearboxes to avoid grinding the gears. First, you'd press the clutch to take the pressure off the dog teeth and allow the gear selector forks and dog gears to slide into neutral, away from the engaged helical gear. With the clutch pedal released, you'd 'blip' the engine to bring the revs up to the speed needed to engage the next gear, clutch-in and move the gear stick to slide the selector forks and dog gear to engage with the next helical gear. THE SYNCHROMESH (OR WHY YOU DON'T NEED TO DOUBLE- CLUTCH) Synchros, synchro gears and synchromeshes - they're all basically the same thing. A synchro is a device that allows the dog gear to come to a speed matching the helical gear before the dog teeth attempt to engage. In this way, you don't need to 'blip' the throttle and double-clutch to change gears because the synchro does the job of matching the speeds of the various gearbox components for you. To the left is a colour- coded cutaway part of my example gearbox. The green cone-shaped area is the syncho collar. It's attached to the red dog gear and slides with it. As it approaches the helical gear, it makes friction contact with the conical hole. The more contact it makes, the more the speed of the output shaft and free-spinning helical gear are equalised before the teeth engage. If the car is moving, the output shaft is always turning (because ultimately it is connected to the wheels). The layshaft is usually connected to the engine, but it is free-spinning once the clutch has been operated. Because the gears are meshed all the time, the synchro brings the layshaft to the right speed for the dog gear to mesh. This means that the layshaft is now spinning at a different speed to the engine, but that's OK because the clutch gently equalises the speed of the engine and the layshaft, either bringing the engine to the same speed as the layshaft or vice versa depending on engine torque and vehicle speed. So to sum up that very long-winded description, I've rendered up an animation - when you see parts of a gearbox moving in an animation, it'll make more sense to you. What we have here is a single gear being engaged. The layshaft the blue shaft with the smaller helical gear attached to it. To start with, the larger helical gear is free-spinning on its slip ring around the red output shaft - which is turning at a different speed because it's connected to the wheels. As the gear stick is moved, the gold selector collar begins to slide the dog gear along the splines on the output shaft. As the synchromesh begins to engage with the large helical gear, the helical gear starts to spin up to speed to match the output shaft. Because it is meshed with the gear on the layshaft, it in turn starts to bring the layshaft up to speed too. Once the speed of everything is matched, the dog gear locks in place with the output helical gear and the clutch can be engaged to connect the engine to the wheels again. Download Video:MP4 : Ogg WHAT ABOUT REVERSE?
Reverse gear is normally an extension of everything you've learned above but with one extra gear involved. Typically, there will be three gears that mesh together at one point in the gearbox instead of the customary two. There will be a gear each on the layshaft and output shaft, but there will be a small gear in between them called the idler gear. The inclusion of this extra mini gear causes the last helical gear on the output shaft to spin in the opposite direction to all the others. The principle of engaging reverse is the same as for any other gear - a dog gear is slid into place with a selector fork. Because the reverse gear is spinning in the opposite direction, when you let the clutch out, the gearbox output shaft spins the other way - in reverse. Simple. The image on the left here shows the same gearbox as above modified to have a reverse gear.
CRASH GEARBOXES OR DOG BOXES. Having gone through all of that business about synchromeshes, it's worth mentioning what goes on in racing gearboxes. These are also known as crash boxes, or dog boxes, and use straight-cut gears instead of helical gears. Straight-cut gears have less surface area where the gears contact each other, which means less friction, which means less loss of power. That's why people who make racing boxes like to use them. Normally, straight-cut gears are mostly submerged in oil rather than relying on it sloshing around like it does in a normal gearbox. So the extra noise that is generated is reduced to a (pleasing?) whine by the sound-deadening effects of the oil.
But what is a dog box? Well - motorbikes have been using them since the dawn of time. Beefing the system up for cars was the brainchild of a racing mechanic who wanted to provide teams with a quick method of altering gear ratios in the pits without having to play "chase the syncro hub ball bearings" as they fell out on to the garage floor. Normal synchro gearboxes run at full engine speed as the clutch directly connects the input shaft to the engine crank. Dog boxes run at a half to a third the speed of the engine because there is a step-down gear before the gearbox. The dog gears in a dog box also have less teeth on them than those in a synchro box and the teeth are spaced further apart. So rather than having an exact dog-tooth to dog-hole match, the dog teeth can have as much as 60° "free space" between them. This means that instead of needing an exact 1-to-1 match to get them to engage, you have up to 1/6th of a rotation to get the dog teeth pressed together before they touch each other and engage. The picture on the right shows the difference between synchro dog gears and crash box dog gears. So the combination of less, but larger dog teeth spaced further apart, and a slower spinning gearbox, allegedly make for an easier-to-engage crash box. In reality, it's still quite difficult to engage a crash box because you need exactly the right rpm for each gear or you'll just end up grinding the dog teeth together or having them bounce over each other. That results in metal filings in your transmission fluid, which ultimately results in an expensive and untimely gearbox rebuild. But it is more mechanically reliable - it's stronger and able to deal with a lot more power and torque which is why it's used in racing. So in essence, a dog box relies entirely on the driver to get the gearchange right. Well - sort of. Nowadays the gearboxes have ignition interrupters connected to them. As you go to change gear, the ignition system in the engine is cut for a fraction of a second as you come to the point where the dog teeth are about to engage. This momentarily removes all the drive input from the gearbox making it a hell of a lot easier to engage the gears. And when I say 'momentary' I mean milliseconds. Because of this, it is entirely possible to upshift and downshift without using the clutch (except from a standstill). Pull the gear out of first, and as you blip the throttle to get the engine to about the right speed, the ignition is cut just as the gears engage. Even the blip of the throttle isn't necessary now either - advanced dog boxes can also attempt to modify the engine speed by adjusting the throttle input to get the revs to the right range first. Of course even with all this cleverness, you still get nasty mechanical wear from cocked up gear changes, but in racing that doesn't matter - the gearbox is stripped down and rebuilt after each race. BEFORE THE GEARBOX - THE CLUTCH So now you have a basic idea of how gearing works there's a second item in your transmission that you need to understand - the clutch. The clutch is what enables you to change gears, and sit at traffic lights without stopping the engine. You need a clutch because your engine is running all the time which means the crank is spinning all the time. You need someway to disconnect this constantly-spinning crank from the gearbox, both to allow you to stand still as well as to allow you to change gears. The clutch is composed of three basic elements; the flywheel, the pressure plate and the clutch plate(s). The flywheel is attached to the end of the main crank and the clutch plates are attached to the gearbox layshaft using a spline. You'll need to look at my diagrams to understand the next bit because there are some other items involved in the basic operation of a clutch. (I've rendered the clutch cover in cutaway in the first image so you can the inner components.) So here we go. In the diagram here, the clutch cover is bolted to the flywheel so it turns with the flywheel. The diaphragm springs are connected to the inside of the clutch cover with a bolt/pivot arrangement that allows them to pivot about the attachment bolt. The ends of the diaphragm springs are hooked under the lip of the pressure plate. So as the engine turns, the flywheel, clutch cover, diaphragm springs and pressure plate are all spinning together. The clutch pedal is connected either mechanically or hydraulically to a fork mechanism which loops around the throw-out bearing. When you press on the clutch, the fork pushes on the throw-out bearing and it slides along the layshaft putting pressure on the innermost edges of the diaphragm springs. These in turn pivot on their pivot points against the inside of the clutch cover, pulling the pressure plate away from the back of the clutch plates. This release of pressure allows the clutch plates to disengage from the flywheel. The flywheel keeps spinning on the end of the engine crank but it no longer drives the gearbox because the clutch plates aren't pressed up against it. As you start to release the clutch pedal, pressure is released on the throw-out bearing and the diaphragm springs begin to push the pressure plate back against the back of the clutch plates, in turn pushing them against the flywheel again. Springs inside the clutch plate absorb the initial shock of the clutch touching the flywheel and as you take your foot off the clutch pedal completely, the clutch is firmly pressed against it. The friction material on the clutch plate is what grips the back of the flywheel and causes the input shaft of the gearbox to spin at the same speed. Burning your clutch You might have heard people using the term 'burning your clutch'. This is when you hold the clutch pedal in a position such that the clutch plate is not totally engaged against the back of the flywheel. At this point, the flywheel is spinning and brushing past the friction material which heats it up in much the same was as brake pads heat up when pressed against a spinning brake rotor (see the Brake Bible). Do this for long enough and you'll smell it because you're burning off the friction material. This can also happen unintentionally if you rest your foot on the clutch pedal in the course of normal driving. That slight pressure can be just enough to release the diaphragm spring enough for the clutch to occasionally lose grip and burn. A slipping clutch The other term you might have heard is a 'slipping clutch'. This is a clutch that has a mechanical problem. Either the diaphragm spring has weakened and can't apply enough pressure, or more likely the friction material is wearing down on the clutch plates. In either case, the clutch is not properly engaging against the flywheel and under heavy load, like accelerating in a high gear or up a hill, the clutch will disengage slightly and spin at a different rate to the flywheel. You'll feel this as a loss of power, or you'll see it as the revs in the engine go up but you don't accelerate. Do this for long enough and you'll end up with the above - a burned out clutch.
Let's not forget that transmission is the most complicated component in a vehicle and it is enough to have one defective component to cause a lot of serious problems. That's why it is so important to have everything fixed and replaced in time: high performance manual and automatic transmissions, clutch sets and torque converters, and much more. If you're looking for the good place to do some shopping online, Performance Transmission Parts section at CARiD.com seems to be a great option. Don’t wait another moment and choose from the great variety of components they offer for your transmission
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MOTORCYCLE 'BASKET' CLUTCHES It's worth spending a moment here to talk about basket clutches as found on some Yamaha motorbikes. Even though the basic principle is the same (sandwiching friction- bearing clutch plates against a flywheel), the design is totally different. If nothing else, a quick description of basket clutches will show you that there's more than one way to decouple the a spinning crank from a gearbox. Basket clutches need to be compact to fit in a motorbike frame so they can't have a lot of depth to them. They also need to be readily accessible for mechanics to be able to service them with the minimum amount of fuss, something that's near impossible with regular car clutches. A basket clutch has a splined clutch boss bolted to the shaft coming from the engine crank with strong springs. Metal pressure plates slide on to this shaft, in alternating sequence with friction material clutch plates. The clutch plates are splined around the outside edge, where they fit into slots in an outer basket - the clutch housing. The clutch housing is bolted on to the layshaft which runs back through the middle of the whole mechanism and into gearbox. Clever, but as usual, not much use without a picture, so here you go.
In operation, a basket clutch is simplicity itself. A throw-out bearing slides around the outside of the layshaft and when you pull the clutch lever, the throw-out bearing pushes against the clutch boss. The clutch boss compresses the clutch springs and removes pressure from the whole assembly. The friction plates now spin freely in between the pressure plates. When you let the clutch out, the springs push the clutch boss in again and it re-asserts the pressure on the system, crushing the friction and pressure plates together so they grip. And there you have a second type of clutch. You should now feel proud that with all your newfound (and somewhat geeky) understanding of clutches, you can go about your business safe in the knowledge that you sort of understand how all this spinning, geared-and-splined witchcraft works. SEQUENTIAL GEARBOXES - WHAT, WHY AND HOW? If you've ever watched motorsports you'll have noticed that the drivers don't have an "H" gate for their gearstick. They either jam the stick back and forth or use paddle-shifters behind the steering wheel. The paddle-shifters do the same job as the gearstick movement in this case, only using electronics to move the shifter. So what's going on in a sequential gearbox? Actually it's quite simple. A sequential gearbox is just like a manual gearbox but the selector system is different. The manual gearbox example at the top of the page showed a series of selector forks which were moved by the physical position of the gearstick. In a sequential box, those selector forks are connected to a single shaft that has corkscrew-type grooves in it. The collar that fits around this selection shaft has a ballbearing in it which sits in a recess in the collar as well as in one of the corkscrew grooves.
When the gearstick is moved forwards or backwards, the selector shaft is mechanically turned by some number of degrees. That twisting motion rotates the corkscrew groove which in turn interacts with the ballbearings and the selector fork collars, forcing them to slide back and forth. Each click of the gearstick rotates the shaft another number of degrees and all the selector forks change position in one go. That's why it's called a sequential gearbox - the gears are always selected in sequence. You can't jump from first to third, you have to go via second. Often, sequential gearboxes have a "double- click for neutral" option and when you do this, it disengages the clutch and rotates the selector shaft back around to the neutral position, just before first gear. So why design and use a sequential gearbox? Well for a start it's a simpler design than a fully-manual gearbox with less moving parts. For racing drivers it makes for much quicker gearchanges - bang the gearstick and you're up a gear nearly instantly. If you want to see how the corkscrew groove interacts with the selector collars this animation is worth watching. Trivia note : TipTronic type gearboxes are not sequential. See the section below for an explanation of why. Download Video:MP4 : Ogg One final point on sequential boxes - if you've ridden a geared motorbike in the last 50 years or so, you've used a sequential gearbox. Most bikes are 1-down, 5-up with neutral in between first and second gear. That little gear selector pedal that you click up and down with your left foot is simply linked to a ratchet system that ratchets the selector shaft around to pick the relevant gear. AUTOMATIC GEARBOXES - WHAT, WHY AND HOW? If you're reading this in America, there's a fair chance that everything above this point in the page was totally useless to you because you don't "drive stick", you drive an automatic. Automatic gearboxes are a totally different beast. For a start they don't have a clutch pedal. For that matter they don't have a clutch at all; they have a torque converter, but we'll get on to that later. If you took an automatic gearbox apart (and for the love of all that is Holy, please don't), you'd see an enormous collection of mechanical parts all jammed into an impossibly small space. Taking centre stage would be the planetary gearset. Not to be confused with planetary drive, a hyperspace system we've only seen on the Sci Fi channel, the planetary gearset is nowhere near as exciting. In a manual gearbox, the dog gears lock and unlock different sets of helical gears to the output shaft in order to give the various gear ratios. In an automatic gearbox, the planetary gearset produces all the different gear ratios in one go and with only one set of gears. Ok so maybe it is pretty cool, but know this - an automatic gearbox is several orders of magnitude more complicated than a manual gearbox. Read on and you'll begin to understand why getting an automatic gearbox overhauled costs so damned much. A QUICK PRIMER ON HOW PLANETARY GEARSETS WORK Any planetary gearset has three main components. The sun gear, the planet gears (and their carrier) and the ring gear. Any one of these three components can be locked in place, but more importantly, any one can be the input orthe output drive. Locking any two of them at the same time will always produce a 1:1 gear ratio. So how the hell does that work? One set of gears for every ratio you need? The work of the Devil? Time to get the old brain massager out again. For this example I'll talk about a planetary gearset with a ring gear that has 75 teeth and a sun gear that has 25 teeth. The following table shows how sending the input to one set of gear and locking another set can give a wide variety of gear ratios. Input Ouput Locked gears Calculation Resulting ratio Sun Planet Carrier Ring 1+(Ring/Sun) 4:1 Planet Carrier Ring Sun 1/(1+(Sun/Ring)) 0.75:1 Sun Ring Planet Carrier -Ring/Sun -3:1 (ie. reverse)
So that table basically has one reverse and two forward gears. Need more gears? Add more planetary gearsets with different numbers of teeth and link them together. Make the ouptut of one become the input of another and you can start to multiply up the number of gears available to you. The image here shows an example planetary gearset with the planet carrier in cutaway. Again, something like this works much better in motion. Below I've rendered an animation showing a planetary gearset in motion. In this example, the blue ring gear is locked. The input is the yellow sun gear and the output is the planet carrier. The planetary gears are the green ones, and the planet carrier is semi-transparent so you can see what's going on inside. This shows clearly how the input to the sun gear can be geared down - in this case by a ratio of 2.7:1. Download Video:MP4 : Ogg Compound planetary gearsets In reality, automatic gearboxes typically use one or more compound planetary gearsets instead of chaining regular gearsets together. They look just like a regular planetary gearset from the outside, but inside there are two sun gears and two sets of intermeshing planet gears. There is still only one ring gear though. With a single compound gearset, the number of ratios available increases to 4 forward ratios and one reverse. The image below shows an example compound planetary gearset again with the planet carrier in cutaway. In my example, the planet gears are arranged as inner and outer planets. The inner ones are shorter and only engage the small sun gear and the outer planet gears. They in turn engage the larger sun gear at the bottom and the outermost ring gear. Another configuration would be to have the two sets of planet gears next to each other but slightly staggered so that only one set meshes with the ring gear. Would you believe there are people paid to come up with this stuff? Makes you wonder if you shouldn't just accept that an automatic gearbox simply works and that you don't want to know why.
I could now go on to explain to you how all the different ratios get selected but if I did, I'd lose most readers at this point and all the typing and fine imagery in the rest of the page would go to waste. For the sake of a working example, I will explain the first two gears though. Looking at the images here, When first gear is engaged, the smaller sun gear (green) is driven from the torque converter. The planet carrier (red) tries to spin the opposite direction but because of a one-way clutch system, it locks in place which forces the ring gear (blue) to turn instead. The ring gear becomes the output from the gearbox in this case and there you have first gear. The catch is that because of the design of the compound gearset, the direction of rotation of the output shaft ought to be opposite to that of the input shaft, but it isn't. This is because the first set of planet gears engages the second set and it's the second set that turns the ring gear. Doing this reverses the direction of rotation, thus making it now the same as the input shaft. Moving swiftly along, when second gear is engaged the input is again the small sun gear but this time the ring gear is held in place by a band and the output becomes the planet carrier. LOCKING PLANETARY GEARSET COMPONENTS
If you've got this far, congratulations, you're doing better than I did the first time I had automatics explained to me. You might now be wondering how the clutches and bands I've mentioned above actually work. Bands are literally that - they're a band wrapped around the outside of the ring gear and when tightened, they lock the ring gear in place. Bands are actuated by a lever or pivot connected to a small hydraulic piston in the gearbox housing. The image here shows how a band might work in the example I've been building up. The actuator piston actually sits in a small cylinder inside the hydraulic distributor (see later) which is built into the gearbox case. You can see the band wraps around the ring gear and when the piston is pushed down, it tightens the band and clamps the ring gear into place, locking it to the gearbox case.
The clutches are a little more complex and are used to perform functions such as locking the sun gears to the turbine or input shaft. Automatic transmission clutches are a lot like the motorbike basket clutches mentioned higher up the page. They consist of a series of pressure and friction plates with splines on the inside and outside. These are compressed by hydraulic fluid fed through channels in the various shafts to a clutch piston. Clutch springs make sure the clutch piston releases when hydraulic pressure is reduced. The example here shows how a clutch system might work to lock the ring gear to the output shaft.
THE AUTOMATIC GEARBOX HYDRAULIC SYSTEM - HOW IT CHANGES GEARS. You've got the idea by now that hydraulics are used a lot in an automatic gearbox. They're used to pressurise the piston plate for the clutches and they're used to move the band-activation pistons up and down. In the good old days, the routing of the hydraulic fluid in the system was controlled by mechanical shift valves linked to the throttle valve on one side and the governor (see later) on the other. Those days are on the way out now and generally speaking, when you move the gear stick, you're doing nothing more than giving an input to the engine management system or engine control unit (ECU) indicating what gear you'd like to be in. The ECU then looks at engine speed, speed across the ground, current gearbox configuration and position of the gear selector and decides what the best action is. It signals solenoid shift valves inside the hydraulic system to open and close appropriately and the gearbox then changes gears as necessary.
But how does the gearbox know to go up gears when you're speeding up, and down when you're slowing down? Well there's a device called the governor attached to the output shaft of the gearbox. It's a centrifugal sensor connected into the hydraulic circuit. The faster you're going, the faster the governer spins and the more open the valve in it becomes. That in turn allows the pressure of the hydraulic circuit to rise, which then applies more pressure to different components, pistons and clutch activators and lets the gearbox shift up at the right speeds. Again, in modern cars, all this information is fed through the ECU which also takes another input from a throttle sensor or more usually a vacuum modulator. These devices allow the ECU to know how hard the engine is working - something else that's critical to how the gearbox operates. It's these inputs that can sense the sudden need for more power so that when you stuff the accelerator to the floor, the gearbox can downshift. The ECU sees a relatively sedate output shaft speed from the governor but a sudden and dramatic increase in vacuum pressure in the engine intake manifold. This is the key to dump the gearbox down a gear to get more power and quick. Limiting gear selection. Most gearbox selectors have a '1' and '2' position. When you select one of these positions you're inhibitting the gearbox's ability to pick any gear higher than that. In a mechanical system it locks off certain portions of the hydraulic system physically so the gearbox simply cannot provide hydraulic pressure to the selector components. In a modern electronic gearbox, again you're simply telling the ECU "don't select anything higher than this". The ECU will then simply not ever send commands to open the solenoid valves to activate higher gears. The pump. It's probably no surprise to you that all this hydraulic trickery needs some sort of pressure to work and that comes from the hydraulic pump. This is normally located in the cover of the gearbox housing itself and it draws fluid from the gearbox sump to feed the gearbox hydraulic system, the fluid cooler (basically a small radiator) and the torque converter. The pump itself is a typically a rotary displacement pump that uses the difference in pressure between the spinning centre lobe and the outer housing to suck fluid in on one side and expel it on the other. For the uninitiated or the morbidly curious, the image above shows a highly simplified example of the rats nest of hydraulic routes in a gearbox housing. The hydraulic lines are effectively cast in the metal because doing it with rubber hoses and clamps would be so complicated and take up so much space that it would be uneconomical and unreliable to do in mass production. PARK IT! So after the long and complicated slog through all that stuff above, are you ready for something simple? Ok, here we go. "P" - the park position on an automatic gear selector. If you've ever engaged park right before you've actually stopped, you'll have heard a clicking sound followed by a thud as the gearbox locks and the car rocks forwards. The mechanism that does this is so disturbingly simple it's almost not worth rendering a picture for. Ready? How about notches on the outside of the clutch housing and a single or pair of spring-loaded catches? Seriously. The image here shows the basic idea behind the park mechanism in an automatic. When you put the gearbox in 'P' for park, the catches are deployed and they fit into the notches on the outside of the clutch housing. Simple.
TORQUE CONVERTERS
Just like a manual gearbox, an automatic gearbox needs a method of decoupling the constantly-spinning engine from the gearbox components. To do this it uses a torque converter which is a viscous fluid coupling (because it's full of hydraulic fluid). A torque converter consists of three basic elements. The impeller, the turbine and the stator. The impeller is attached to the torque converter housing which itself is attached to the engine flywheel. The impeller is basically a centrifugal pump. As the flywheel spins, so does the impeller and the vanes take the fluid from the central part of the torque converter and fling it to the outside creating a pumping action. The fluid then circulates around the outer edge of the torque converter and back into the turbine. The turbine is basically the opposite of the impeller - it's like a ships's propeller in that the fluid passing through it causes it to spin. The turbine is connected to the input shaft of the gearbox via a splined shaft so as the turbine spins, so does the input shaft to the gearbox. The fluid passes through the turbine from the outside towards the inside. Finally, as the fluid reaches the central core, it passes through the stator which is designed to help redirect the flow into the inner vanes of the impeller. (Without the stator, the whole system would be a lot less efficient) With this mechanism, the fluid is constantly being circulated. In the image here I've rendered the various parts of an example torque converter taken apart so you can see the internal construction.
When the engine is idling, the fluid is pumping around without a lot of force and the amount of torque on the turbine is minimal. As you accelerate, the impeller speeds up and creates larger forces on the turbine which in turn spins more quickly and with more torque. Because it's connected to the input shaft of the gearbox, this feeds more rotational speed and torque into the gearbox and the car starts to move forwards. It's because of this viscous liquid coupling that automatic gearboxes have a certain amount of 'slop' in them - the engine can rev up and down without the car actually changing speed too much. It's also the reason automatics are less fuel efficient because the torque converter uses up energy from the engine simply in its design by spinning the hydraulic fluid. In the image here I've rendered a close-up cutaway of an assembled torque converter. The yellow arrow is my attempt to show the basic circulation path of the fluid inside as it is pumped from the impeller (red) through the turbine (blue) and back through the stator (green). For sportier vehicles or those with specialised needs, some torque converters include a hydraulic clutch. Once the car is moving and in top gear, the clutch engages and locks the turbine to the impeller. Once that happens, the whole torque converter spins as one and the viscous coupling becomes redundant - effectively the gearbox now behaves like a manual because the engine flywheel is connected directly to the gearbox input shaft. By locking all the components together, it makes the car as fuel efficient as a manual when in top gear because the energy that was being used up in the viscous coupling is no longer required. It also means instantaneous throttle response - you push the accelerator and the car accelerates instantly just as with a manual. But why is it called a torque converter? Very simply, because it has the ability to multiply the torque from the engine 2 or 3 times in certain conditions. Basically, from a standing start, when the engine is spinning far faster than the gearbox, the whole design allows the torque from the flywheel to be multiplied. As the car gets up to speed, the multiplication factor drops until it becomes 1x once everything is in motion and the impeller and turbine are moving at almost the same speed.
Doing it yourself. In true Blue Peter fashion, you can demonstrate the principle behind a torque converter at home. Get a large bucket or bowl and a cordless drill with a paint- stirrer. Fill the bucket with water and put some bits of paper around the outside of the bucket, floating on the water. Stuff the paint stirrer in the middle and pull the trigger on the drill. To start with, the paint stirrer is spinning way faster than the water in the bucket, and the bits of paper will barely be moving. As the water in the bowl begins to speed up its circulation, the bits of paper will being circulating the bucket at speed. Eventually the water in the bowl will be circulating at almost the same speed as the paint stirrer is turning. (At this point your wife/husband will probably also be complaining that it's going all over the kitchen/bathroom - you've been warned) It's that "almost" that shows the inefficiency in a torque converter - the fluid can never spin at exactly the same speed and thus it can never impart the exact same torque and motion into the turbine. Now imagine that the bucket or bowl has vanes around the inside of it. As the water is circulating, it's going to be applying force to those vanes and given a slippery enough surface, your bucket or bowl will eventually start to spin. Voila. The drill and the paint stirrer are the input from the engine and the spinning bucket or salad bowl is the output to the gearbox. The other way to do this is to take two desk fans and turn one on and point it at the other. Eventually the second fan will start to spin because of the air being forced past it by the first fan. This uses the same principle but with moving air instead of water and it's nowhere near as much fun to watch
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TIPTRONIC® GEARBOXES
If you've owned a VW or Audi in the last few years it might have come with a TipTronic® gearbox. To you, the driver, it looks like a regular automatic gearbox but with with an H- gate for the gearshift. In normal operation, you use the gearbox just like an automatic, putting it in 'D' for Drive and just letting it go about its business. But if you click the gearstick over into the H-gate it becomes a discrete automatic, meaning you can then click it fowards and backwards like a sequential gearchange. In this mode you are basically telling the gearbox when you want it to shift rather than allowing it to shift for you. When you click it forwards for example, you're indicating a desire to go up a gear. The ECU looks at the engine speed, road speed, torque and load and if all the planets align, it shifts up by activating the relevant solenoid valves in the automatic hydraulic system. Most TipTronic® designs do have a certain amount of idiot-proofing though, and if you try to rev the tits off the engine in first, it will override you and automatically shift up to second to save the engine. These types of gearboxes often have steering-wheel shifters either as buttons or triggers on the steering wheel (like the Mazda MX-5) or paddle- shifters. TipTronic® is actually a design from Porsche and they simply license it to other vendors, typically German manufacturers. Because it was one of the first designs to come to the mass market, this type of discrete automatic automatic gearbox is now often referred to as TipTronic® even if it isn't one of the VW/Audi/Porsche ones. Here's a non-comprehensive list of some of the manufacturers and their TipTronic® type shifts: Acura: Sequential SportShift. Audi: Tiptronic, Multitronic (CVT). BMW: Steptronic. Chrysler/Dodge: AutoStick. Citroën: Sensodrive. Ford (Australia): Sequential Sports Shift. Honda: iShift, S-matic, MultiMatic. Hyundai: Shiftronic, H-Matic. Infiniti: Manual Shift Mode. Jaguar: Bosch® Mechatronic. Lexus: E-Shift. Mazda: Sport AT. Mercedes- Benz: TouchShift. MG-Rover: Steptronic. Mitsubishi: INVECS, INVECS II, Sportronic, Tiptronic. Nissan: Tiptronic. Vauxhall/Opel: Easytronic. Peugeot: 2Tronic. Pontiac: TAPshift. Saab : Sentronic. Subaru: Sportshift (system developed and name used under license from Prodrive Ltd.). Smart : Softip. Volkswagen : Tiptronic. Volvo: Geartronic SEMI-AUTOMATIC GEARBOXES Despite the name, these are actually an advanced type of manual gearbox. It's better to refer to them as clutchless manual gearboxes because that more accurately describes what they are. Semi-automatics do not use planetary gearsets and torque converters; they use layshafts, output shafts, clutches and selector forks just like a manual. They come in three flavours, all of which have the same internal mechanisms. Two of those use the familiar paddle-shifters or up-down gearstick for changing gears. (This begins to explain why you cannot simply look at a gearstick or paddle-shifter and tell what the gearbox is. Up/down gearsticks or paddleshifters can both control sequential manual, clutchless manual or TipTronic® type gearboxes.) The third type has a pure manual gearstick. None of the three types have a clutch pedal though so how do they work? Well in the case of the first type, when you click the gearstick up or down, or press one of the paddleshifters, a hydromechanical system disengages the clutch and then moves the gearbox selector forks into the position for the next gear before re-engaging the clutch. Because the system takes inputs from load- and torque-sensors as well as road speed, throttle position and engine demand sensors, and because it's all computer controlled, it can shift more quickly and more smoothly that you or I ever could. The third type uses the same hydromechanical system underneath but has additional sensors coupled to the gearstick. With this type, the action of moving the gearstick out of the gate for one of the gears (for example pulling it back from first) passes a hall effect sensor which tells the clutch to disengage. When you push the gearstick into the gate for the new gear, another hall effect sensor detects the final position of the gearstick and tells the clutch to re-engage. Effectively it's identical to driving a manual car only without a clutch pedal. Clutchless manual gearboxes have appeared under many different names such as Saxomat and Olymat (Fiat 1800, Saab 93, some BMWs and Opels). DSG / DCT GEARBOXES - WHAT, WHY AND HOW? How does this sound? A manual gearbox that's always in two gears at the same time. Sounds impossible, right? Scroll back up to the top of the page and look at how a manual gearbox works - how can this happen? Enter stage left the dual clutch transmission (DCT) or direct-shift gearbox (DSG). Two different names for essentially the same design. The most famous / common of these currently is the DSG as fitted to the Audi TT and some of the newer VW Golfs. The DSG is licensed technology from BorgWarner, which despite sounding like a horrible accident between a Star Trek character and a large movie studio, is an automotive parts supplier known until this point for its automatic gearboxes. The principle is really simple even if the engineering is really complex. The idea is that when you're going up through the gears, increasing in speed, one clutch has the current gear engaged and a second clutch has the next gear up pre-engaged ready to use in the blink of an eye. Technically, that's not even true because a DSG can shift gears in 8 milliseconds. At 400 milliseconds it takes you 50 times longer than that to blink. That in essence is the key benefit to the DSG - blisteringly fast gearchanges. Plus, because one clutch engages as the other one disengages, the time that the gearbox is not driven under power is minimised. So how does this work? Well a DSG gearbox has one layshaft like a normal gearbox, but two output shafts that mesh to a third shaft which goes to the differential. One output shaft has 1st, 3rd and 5th gears on it whilst the other has 2nd, 4th and 6th. The layshaft is actually two shafts one inside the other connected to two concentric 4-plate basket- type clutches at the end. In first gear, one clutch is engaged and the central layshaft is connected to the engine. Selector forks have the first dog-gear engaged with the first helical gear and the car is moving forwards. At the same time though, on the second output shaft, the second dog gear is already engaged with the second helical gear. Because the outer clutch on the layshaft is disengaged though, there is nothing driving this second gear and the outer layshaft is simply spinning freely. At the point when the gearbox needs to shift up, it simply engages the second clutch at the same moment it disengages the first and the outer layshaft is now being driven from the engine. Because second gear was already engaged there is literally no delay in shifting so the gearchange is near instantaneous. Once in second gear, the inner layshaft is now freewheeling as the selector forks engage third gear on the first output shaft and so on and so forth.
The three images here show my typical manual gearbox example modified into a 5- speed DSG. In the first image, first gear is engaged and second gear is pre-selected. The transmission of power from the engine to the output shaft is shown with the green components. The dual clutch (shown in cutaway) has engaged the inner set of friction plates which are connected to the outer layshaft. The first dog-gear is engaged with the first helical gear. In the second image, second gear is selected and third gear is pre-selected. Again, the transmission of power is shown with the green components. This time the dual clutch has engaged the outer set of friction plates that are connected to the inner layshaft. The second dog-gear was already engaged with the second helical gear and so is now driving the output shaft. The final image shows a cutaway of a simplified dual-clutch, dual-layshaft so you can see how the friction plates, layshaft and gears all relate to each other. The green inner layshaft has the drive gears for second and fourth whilst the outer red layshaft has drive gears for first, third and fifth. The grey clutch housing contains all the springs and hydraulics used to engage the various clutch plates, although they're not rendered in this view. CVT (CONTINUOUSLY VARIABLE TRANSMISSION) - WHAT, WHY AND HOW? As they say in some circles, it's all downhill from here. Seriously. If you got your head around DSGs and automatic boxes, the rest of this page is going to be a veritable walk in the park, starting with the CVT - continuously variable transmission. CVTs are based on simplicity rather than complexity. Gone are the nightmare of spinning, whirling, intermeshing gears, cluches, clamps, bands, friction plates etc etc ad nauseum. Instead, the CVT essentially has three moving parts. No seriously. Read on. If you live in the Netherlands, you're intimately familiar with the CVT - most brommers have a dry-belt CVT. For those unfortunate enough to have never lived there, a brommer is a small moped - typically less than 50cc in capacity. They're all two-stroke engines and they are uniquely identifiable from their sound - a constant pitched engine. No revving up and down, just a long, continous high-pitched drone, like bees on crack. It's a gorgeous sound. In fact the role that the Netherlands play in the CVT story is that dr. Hub van Doorne Invented the first CVT for automotive use in 1958. It was the Variomatic and it was used in DAF Cars Doornes Auto Factory.The first variomatic used rubber composite belts, but the durabilaty and strength of these belts just wasn't up to the job for serious car engines. This led to the development of a metal belt which allowed the normally slack side of the belt to actually push, and so was able to deal with higher torque values (up to 450Nm). The modern pushbelt is made up of hundreds of individual, specially designed steel elements, which are strung together along 2 high- alloy steel ring packs. Not so much of the rubber band any more. This product was sold by a new company by dr. Van Doorne - VDT - van Doornes Transmissie (transmission). In 1995 German multinational Robert Bosch Gmbh bought the VDT plant. In 2008, the stats for the factory were about 1100 employees producing about 2.4 million pushbelts. Nissan, Toyota, Mitsubishi, Hyundai, Jeep, Mercedes and Subaru are some of the manufacturers now employing CVTs although not all of them are buying direct from Bosch. Some buy belts produced under license by other transmission manufacturers such as JATCO, Fuji Heavy Industries (Subaru) and Punch. Japan is today's biggest market for pushbelt CVT's. Bosch have a CVT Pushbelt promo video available if you're interested. But I digress. In 2005 CVTs really moved into the mainstream when Nissan introduced the "no shift shock" gearbox into their cars and SUVs. This followed a somewhat faltering start from Ford in 2004 who, frankly, botched the launch of their CVT so badly that barely anyone remembers it. So what the hell makes it so attractive to the automotive and motorcycling markets? Well apart from the simplicity, it has one extremely sound engineering principle: get the engine to peak torque and keep it there whilst infinitely varying the transmission. That way the engine is always performing at peak capacity. No changing gears, no revving up and down the rev range, and as Nissan so aptly put it - no shift shock. Interesting factoid: CVT's were banned from Formula 1 in 1994 because they were making the cars too fast... TWO PULLEYS AND A BELT. IT REALLY IS THAT SIMPLE. So how does this magical CVT work? Simply. Very simply. The most basic CVT has two variable pulleys and either a steel-core rubber pull-belt or a steel alloy push-belt. One pulley is connected to the flywheel and the other to the gearbox output shaft. The belt loops around between the two. On simple scooter-type CVTs, the pulleys change geometry simply by rotational forces - the faster the engine pulley spins, the more it closes up and the faster the output pulley spins, the more it opens out. In automotive applications, the geometry of the pulley is governed by a hydraulic piston connected to the ECU. The pulley itself is basically a splined shaft with a pair of sliding conical wedges on it (called 'Sheaves'). The closer the wedges are together, the larger the radius 'loop' the belt has to make to get around them. The further they are apart, the smaller the radius 'loop' the belt has to make. Based on the principles established right at the top of the page when I was talking about intermeshing gears, if the flywheel pulley has a small radius and the output pulley has a large radius, then the transmission is essentially in low gear. As the car gets up to speed, the two pulleys are adjusted together so that they present an infintely changing series of radii to the belt which ends up with the flywheel pulley having the largest radius and the output pulley having the smallest. On then to the pictures.
The image on the left shows the basic layout of a pulley-based CVT with the two sliding pulleys and the drive belt. This is the equivalent of 'low gear' - the drive pulley spins two or three times for each rotation of the output pulley. It's the equivalent of a small gear meshing with a large gear in a regular manual gearbox. The image on the right shows the same system in 'high gear'. The drive pulley has closed up forcing the drive belt to travel a larger radius. At the same time, the output pulley has pulled apart giving a smaller radius. The result is that for each turn of the drive pulley, the output pulley now spins two or three times. It's the equivalent of a large gear meshing with a small gear in a regular manual gearbox. The difference here is that to get from the low gear to the high gear, the infinite adjustment of the position of the pulleys basically means an infinite number of gears with no point where the drive is ever disconnected from the output. Sweet. TOROIDAL CVT (NISSAN EXTROID) As good as a belt-driven CVT is, the weak link is the belt. If it gets damaged in any way, the transmission becomes useless. Another solution then is the toroidal CVT which is equally as simple in operation but has parts which are less prone to wear than the belt- drive type. With a toroidal CVT, both the input and output shafts are sculpted metal discs that face each other. In between are two rollers that free-wheel on their x-axis, making contact with both discs. The position of the rollers is controlled hydraulically and they pivot in their z-axis around a common centre so that wherever they are in their rotation, the rollers always touch the discs. Because the position of contact changes on the discs, the relative rotation of each disc changes.
The image to the left shows a toroidal CVT in low gear. The input shaft is on the left. As it spins, the rollers make contact on the surface of it in the area I've shaded red. This spins both rollers on their x-axes, and because they both touch the output disc, it is spun in turn. The contact area on the surface of the output disc scribes a much larger circle - again rendered in red. Going back to the most basic stuff you learned earlier, this is the equivalent of a small gear driving a large gear - the gearbox is effectively in low gear. For a toroidal CVT to increase the output shaft speed, both the rollers are pivotted slowly about their y-axes. As they do this, their point of contact on the input and output discs changes in an infinitely smooth, continous motion. Effectively, the radius of the path on the input disc gets larger and larger as the radius of the path on the output disc gets smaller and smaller. This creates and infinite number of gear ratios until 'top gear' is reached when the rollers are in the opposite position to where they started. Now you can see the equivalent of a large gear driving a small gear - the gearbox is effectively in high gear. (right) This type of infinitely adjustable toroidal CVT can deal with very high torque figures and can be stacked up end-to-end to provide other gearing options, and is essentially how the system in some of the JDM and Nissan home-market and CVT gearboxes works (think Skyline 350 GT-8). This last image shows a double-toroidal Nissan Extroid CVT configuration.
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DIFFERENTIALS - THEY'RE WHY YOU CAN TURN CORNERS
With one or two exceptions, every car has a differential. This was a great surprise to an insurance adjuster I spoke to a few years back when he came to process a claim. He eloquently informed me that my claim was being rejected because my car didn't have a differential to replace. In the following few paragraphs you'll learn why that loss adjuster was talking bollocks. So how best to begin to talk about differentials? I suppose to start with you need to understand a very simple concept to do with circles. When you make a car go around a corner, the outer wheels travel further than the inner wheels. Have a look at the diagram here to see what I'm talking about. The first thing you'll notice is that the rear wheels take a different path to the front wheels, but the other thing to notice is that because the car's wheels are describing different radius arcs, the further away from the centrepoint of the arc, the larger the distance that gets travelled. In car terms, that means the outer wheels need to turn more times than the inner ones every time you go around a corner, because they're describing a larger arc. The brighter ones amongst you will now have figured out that if the outer and inner wheels were joined together with a solid axle, one of them could not turn more times than the other - they'd have to turn at the same rate. That, dear reader, is the crux of the matter. Differentials basically allow two wheels on the same axle to turn at different rates. (As well as allowing the wheels on the same axle to turn at different rates, the differential also acts as the final gear reduction in the driveline.) IS THERE A DIFFERENTIAL ON EACH AXLE? That depends. On a two-wheel-drive car, no. Only the driven axle needs a differential. The undriven wheels are not connected to each other so the differential is a moot point. For four-wheel-drive or all-wheel-drive vehicles, then yes, both the front and rear axles will have differentials because they are both driven axles. Technically, a differential is a torque-splitter - it splits the input torque two ways to two output shafts, each of which can turn at a different rate. For full-time all-wheel-drive, there is often a third differential in the driveline from the front to the rear of the vehicle, to allow the entire front and rear axles to spin at different speeds to each other. The difference between the various drive systems is illustrated later on this page in the section on 2WD, 4WD and AWD. OPEN DIFFERENTIALS We'll deal with open differentials first because they're the easiest to explain, they're the most common, and they supply the same amount of torque to each output. Open differentials have a few essential components, illustrated below. The input pinion gear is the gear that is driven from the drivetrain - typically the output shaft from the transmission. It drives the ring gear which, being larger, is what gives that final gear reduction I mentioned. Attached to the ring gear is the cage, containing two captive pinion gears that are intermeshed with the two output pinion gears, one connected to each axle. The captive pinions are free to rotate how they wish.
As the input pinion spins, it meshes with the ring gear. The ring gear spins, spinning the cage and the two captive pinions. When the vehicle is travelling in a straight line, neither drive pinion is trying to spin any differently from the other, so the captive pinions don't spin and the turning of the ring gear is translated directly to both drive pinions. These are connected to the driveshafts to the wheels, so effectively, the ring gear spins the wheels at the same speed that it is turning. When the vehicle starts to turn a corner, one of the wheels is going to want to spin more quickly than the other. At this point, the captive pinions come into play, allowing the two drive pinions to spin at slightly different speeds whilst still transmitting torque to them. Clever. You can tell if your vehicle's differential is working properly by jacking the driven axle up off the ground and spinning one wheel. When you do, because the gearbox is stationary, it holds the ring gear solid, the captive pinions spin in opposite directions, and the other wheel on the axle spins the other way around. This also explains why a two-wheel-drive vehicle can get into trouble when one wheel has less friction with the ground than the other. The open differential cannot compensate for this. If one drive pinion is held solid compared to the other, then all the input gets redirected to the drive pinion that has the least resistance. This is why when you gun a two-wheel-drive car with one wheel on ice and the other on the road, the wheel on the ice spins and the wheel on the road doesn't. You don't go anywhere because all the engine power is directed to the wheel with least resistance - the one on the ice. Imagine the same scenario on a four-wheel-drive vehicle that has open differentials on the front and rear. If you're off-roading in such a vehicle and get it into a situation where one front wheel and one rear wheel are off the ground, you're stuck. The differentials will spin the airborne wheels and send no torque to the ones on the ground. That leads us nicely on to the next topic : LIMITED-SLIP DIFFERENTIALS Sometimes known by the "positraction" moniker, the simplest form of limited-slip differential is designed to combat the scenario outlined above. Physically there's not a lot of difference in the design of a limited-slip differential. It still has all the components of an open differential but there is two crucial extra elements. The first are spring pressure plates which are a pair of springs and pressure plates nestled in the cage between the two drive pinions. These push the drive pinions outwards where the second extra element comes into play - clutch packs. The backside of the drive pinions have friction material on them which presses against clutch plates built into the cage. This means that the clutch is always going to try to behave as if the car was moving in a straight line by attempting to make both output pinions spin at the same speed as the ring gear and cage. However, when a car with a limited-slip differential goes into a corner, there are enough forces at play that the drive pinions begin to slip against the clutch material, thus allowing them to turn at different speeds again. The stiffness of the spring pack coupled with the friction of the clutch pack together determine the amount of torque required to overcome the clutch.
So lets go back to our hapless driver stuck with one wheel on the ice and another on the road. With a limited-slip differential, because of the spring- and clutch-packs, even though one wheel is on the ice, the differential is going to attempt to spin both drive pinions at the same speed. With low engine revs and steady throttle control, the wheel on the road will get enough spin to move the vehicle forwards. If the engine is revved hard though, it can still generate sufficient torque to overcome the clutch pack and once again, only the wheel on the ice will spin. To get around this, it's a good idea to try to pull away in second gear - that gives the limited-slip differential a chance to do its job. The render here shows the generic open differential from above modified to be a limited-slip differential.
TORSEN DIFFERENTIALS Torsen differentials are a derivative of open differentials. They derive their name from their function - Torque-Sensing. When the torque going to both outputs is the same, a Torsen differential essentially works just like an open differential. The change comes when the torque going to each output begins to change, for example as a result of a slippery road surface under one wheel. When this happens, what's known as an Invex gear train (inside the differential) begins to bind together.
The Invex gear train is designed with a torque bias ratio in mind that determines the ratio of torque that it can split between the outputs as the geartrain begins to bind together. A 3:1 Torsen differential, for example, can deliver three times the torque to the output that has more traction. The downside of this is that if one output suddenly ends up with no traction at all, the differential won't be able to supply any torque to the other output. Using the 3:1 example, one output can have up to three times the torque than the other. If one output has zero traction, then three times zero is zero, so the other output also gets no torque. That's a gross simplification of how the system works too. If you're really interested, Torsen Traction have some good engineering articles on their website. Torsen differentials are normally used in-line between the front and rear drives for performance all-wheel-drive vehicles, to split the torque between the front and rear axles, rather than the left and right wheels. HOW DOES A TORSEN 'SENSE' TORQUE? The Invex geartrain is essentially a set of helical-cut gears that all mesh together and torque-sensing is actually a bit of a misnomer. The Torsen differential is an entirely mechanical affair with no clutches, hydraulics, actuators or sensors. It doesn't really 'sense' anything. If you look at the rendering above, you can see the Invex gears mesh with the helical drive pinions. At the ends of the Invex gears are regular-cut gears that mesh with each other. So in this example, looking at the top pair of Invex gears; the left gear meshes it's helical-cut part with the helical left drive pinion, and it meshes it's regular-cut part with the right Invex gear. That gear in turn meshes its helical-cut part with the right helical drive pinion. It's this interconnectivity that allows the Torsen to work like an open differential when the torque is even, but as a torque-sensing unit when its not.
Where the helical cuts mesh together (shown in close-up in the rendering on the right), there's a certain amount of friction inherent in that design. The angle of the helical spiral used to create the gears determines the amount of force required to make them turn. The shallower the pitch of the spiral, the more force required, and hence the more torque required to turn two meshed gears. That's the clever part then - the spiral pitch. The precise spiral pitch angle determines the torque bias ratio. The whole system works on simple high-school physics. Remember the experiment where you had two blocks of wood with sloped cuts and you had to determine the downward force required to make the top block slide along the slope of the bottom block? It's the same principle. The steeper the slope, the less force required to make the block slip. With helical gears, the steeper the pitch of the spiral, the less torque required to make them mesh together. LOCKING DIFFERENTIALS Locking differentials are another derivative of open differentials but with an electronic, pnuematic or hydraulic actuation system that locks the two drive pinions together as if they were a solid axle. This is for use in serious off-roading, where a vehicle will spend a lot of time with one wheel per axle in the air. By locking the differential, it behaves like a solid axle and both wheels are spun together. THE EXCEPTIONS THAT PROVE THE RULE Remember I said that there were a couple of exceptions? A good example of a vehicle with no differential would be a NASCAR or Indy car racer. To save weight, those cars have no differential. "Ah yes," I hear you say, "but they go around corners so they must have differentials!". Well - yes, and no. With the exception of street courses, NASCAR and Indy car racers always turn left, and this is Good News for the engineers. When you know that a vehicle is always going to be turning one direction, you can make the outer tyres physically larger than the inner ones. This gives them a greater circumference, and that in turn means that for every turn of the axle, the outer tyre is going to try to travel further than the inner one - precisely what you need in a corner. For the straights, these racers live with the scrubbing that happens when the tyres try to travel different distances because 90% of the time they are cornering. AWD COUPLINGS VISCOUS COUPLINGS Viscous coupling aren't really a type of differential but they're worth mentioning because they're used a lot in all-wheel drive vehicles. Lower end AWD vehicles are actually mostly 2-wheel drive vehicles (see the article below for all the differences) until the front wheels begin to slip. When that happens, they become all-wheel-drive through the use of a viscous coupling. In it's most simple form, it's essentially identical to the torque converter found in an automatic gearbox. For a full description of how that works, see torque converters up above. HYDRAULIC CLUTCH COUPLINGS Again, not really a differential, but another type of device used in AWD cars to engage the rear differential. With these types of coupling, the front and rear differentials drive hydraulic pumps - normally filled with oil. Any difference in the speed of the two pumps causes a pressure imbalance in the system that activates a clutch pack in-line to the rear differential to engage it. So again, when the front wheels spin faster than the rear (meaning slip), the clutch pack is engaged and the rear differential comes into play. These types of coupling typically also have braking and thermal overrides so that if the gearbox oil in the rear differential becomes too hot, or the car is braking, the clutch pack can be overridden and disengaged (without this, ABS-equipped vehicles would not be able to sense all four wheels correctly under braking).
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2WD, 4WD, AWD Ok so in the last couple of pages you've now seen a lot of references to 2WD (two- wheel drive), 4WD (four-wheel drive) and AWD (all-wheel drive). Time to explain the differences. 2WD - TWO-WHEEL DRIVE
This is by far the most common type of drivetrain in any car today. The engine drives the gearbox which sends its output to an open differential either on the front or rear axle, which in turn drives those wheels. If one of the driven wheels comes off the ground, or gets on a slippery surface like ice, the car gets stuck because all the torque is being sent to that wheel whilst the other three sit there helpless.
4WD - FOUR-WHEEL DRIVE Also known as part-time all-wheel drive, this system has an open differential on the front and rear axle and a transfer case on the output from the gearbox. Typically 4WD is normally driving the rear axle with the front axle only coming into play in 4WD mode. The transfer case is the device that splits the torque between the front and rear axles. It typically has some sort of selectable internal differential or viscous coupling to allow the front and rear drives to turn at different speeds if need be. Some trucks and SUVs have a selector with 2H, 4H and 4L on it - it looks like a second gear shift. This is actually controlling how the front and rear outputs of the transfer case get locked together. In 2H mode (2-wheel drive, high), it essentially disconnects the front output completely and only drives the rear axle. In 4H mode (4-wheel drive, high), it engages the front output via the viscous coupling so that the axles can turn at different speeds, and now sends torque to both open differentials. In 4L mode (4-wheel drive, low) it engages a second set of reduction gears and locks the front and rear axles together so they must spin at the same speed. This would be bad for on-road driving because it does not allow any difference in speed between the front and rear wheels, so you'd often get dragging and slipping which would make the car essentially unsafe to drive. However, locking everything together like this and reducing the gear ratio makes perfect sense for off- roading, which is why it's an option. However, with open differentials, it's still entirely possible to get stuck with a 4WD vehicle. If you're off-roading and the front-left and rear- right wheels both leave the ground together (for example), then the torque will all be sent to those wheels and they'll spin helplessly in the air. Locking, limited-slip or Torsen differentials solve this but add weight, complexity and cost to the system. Locking hubs On older 4WD systems, the front wheels could only be engaged to the transfer case by locking hubs. Essentially the transfer case was always sending torque to the front driveshaft and had no viscous coupling. To get into 4WD mode, the driver had to stop and get out, and lock the front wheels to the axles so they could be driven. In newer 4WD systems, the lockable hubs are still present on some models, but are designed more for mechanical sympathy and fuel economy than anything else. With the hubs onlocked, the whole front part of the drive system isn't being dragged along for the ride, which causes mechanical wear and a drop in fuel economy. AWD - ALL-WHEEL DRIVE TYPE 1
Finally, all-wheel drive or full-time 4WD. Found mostly on sportier cars, but also on some SUVs, there are two types of AWD, both designed to try to overcome the problems with 4WD. The simplest form has two open differentials - one on each axle - and a viscous coupling between. The engine drives the gearbox which drives two output shafts. One goes to the front open differential and the other goes to the viscous coupling, the output of which is connected to the rear open differential. Under normal conditions, this type of AWD system functions exactly like a 2WD car, driving only the front axle (unlike a 4WD which normally drives the rear axle). Lower end Subarus and some of the Honda trucks use this system. The front wheels turn at a certain rate, and the rear wheels are dragged along for the ride. Both halves of the viscous coupling are spinning at the same speed so no torque is sent to the rear axle. If the front wheels begin to slip and spin, the input to the front of the viscous coupling begins to spin faster than the rear and because of its torque-converter-like design, this causes the rear output to want to speed up. At this point, the drivetrain is now transferring torque to the rear axle and the car starts to function in AWD mode. Actally, AWD is a bit of a misnomer at this point, because unless the car has limited-slip differentials front and rear, it's still only really driving two wheels in this mode - the one on the front and the one on the rear axles that have the most traction. That leads us nicely on to..... AWD - ALL-WHEEL DRIVE TYPE 2 This is the other type of AWD found on higher-end Subarus, rally cars, expensive sports sedans and such. Very similar to the type 1 AWD, it replaces the viscous coupling with a Torsen differential, and replaces the open differentials front and rear with either Torsen or limited-slip differentials. This is the only true all-wheel-drive system because it will always drive all four wheels. It's also bloody expensive and it saps gas-mileage because of all the extra drag induced in the driveline. But then if you're into performance off- roading, gas-mileage really isn't your primary concern.
FWD, RWD, FE, ME, RE Not to be confused with the descriptions aboe, these acronyms determine the engine location and driven axle(s) on a car. FWD = front-wheel drive. RWD = rear-wheel drive. FE = front engine. ME = mid engine. RE = rear engine.
The position of the engine, being the heaviest part of the car, affects how the car handles. Most vehicles are front-engined, front-wheel drive (FE-FWD) with the engine, gearbox and differential all clustered together in one place. BMWs and other higher-end vehicles are front-engined, rear-wheel drive (FE-RWD) with a propshaft going from the gearbox and engine at the front to the differential at the rear.
Sports cars like the Toyota MR2 and the McLaren F1 are mid-engined. Putting the engine as close to the middle of the car as possible gives the best possible front-to-rear weight distribution and gives predictable, even handling. Mid-engined cars are typically rear-wheel drive (ME-RWD).
Finally, rear-engined vehicles such as most Porsches and the original VW Beetle have the engine, gearbox and differential all clustered at the rear of the car and are typically rear-wheel drive (RE-RWD). The downside of this is that when cornering, with that much weight at the back of the vehicle, it can behave like a pendulum and induce chronic oversteer in corners. THE SUSPENSION BIBLE WHAT DOES IT DO? Apart from your car's tyres and seats, the suspension is the prime mechanism that separates your bum (arse for the American) from the road. It also prevents your car from shaking itself to pieces. No matter how smooth you think the road is, it's a bad, bad place to propel over a ton of metal at high speed. So we rely upon suspension. People who travel on underground trains wish that those vehicles relied on suspension too, but they don't and that's why the ride is so harsh. Actually it's harsh because underground trains have no lateral suspension to speak of. So as the rails deviate side-to-side slightly, so does the entire train, and it's passengers. In a car, the rubber in your tyre helps with this little problem, while all the other suspension parts do the rest. In it's most basic form, suspension consists of two basic components: SPRINGS These come in three types. They are coil springs, torsion bars and leaf springs. Coil springs are what most people are familiar with, and are actually coiled torsion bars. Leaf springs are what you would find on most American cars up to about 1985 and almost all heavy duty vehicles. They look like layers of metal connected to the axle. The layers are called leaves, hence leaf-spring. The torsion bar on its own is a bizarre little contraption which gives coiled-spring-like performance based on the twisting properties of a steel bar. It's used in the suspension of VW Beetles and Karmann Ghias, air-cooled Porsches (356 and 911 until 1989 when they went to springs), and the rear suspension of Peugeot 205s amongst other cars. Instead of having a coiled spring, the axle is attached to one end of a steel shaft. The other end is slotted into a tube and held there by splines. As the suspension moves, it twists the shaft along it's length, which in turn resist. Now image that same shaft but instead of being straight, it's coiled up. As you press on the top of the coil, you're actually inducing a twisting in the shaft, all the way down the coil. I know it's hard to visualise, but believe me, that's what is happening. There's a whole section further down the page specifically on torsion bars andprogressive springs. SHOCK ABSORBERS These dampen the vertical motion induced by driving your car along a rough surface and so should technically be referred to by their proper name - dampers. If your car only had springs, it would boat and wallow along the road until you got physically sick and had to get out. It would be a travelling deathtrap until the incessant vibration caused it to fall apart. Shock absorbers (dampers) perform two functions. As mentioned above, they absorb any larger-than-average bumps in the road so that the upward velocity of the wheel over the bump isn't transmitted to the car chassis. But secondly, they keep the suspension at as full a travel as possible for the given road conditions - they keep your wheels planted on the road. You want more technical terms? Technically they are velocity-sensitive hydraulic damping devices - in other words, the faster they move, the more resistance there is to that movement. They work in conjunction with the springs. The spring allows the wheel to follow the road, moving up and down. The kinetic energy of that moving unsprung mass is transmitted to the damper where it is dissipated. The damper does this by forcing gas or oil through a constriction valve (a small hole). Adjustable shock absorbers allow you to change the size of this constriction, and thus control the rate of damping. The smaller the constriction, the stiffer the suspension. Phew!....and you thought they just leaked oil didn't you? A MODERN COIL-OVER-OIL UNIT
The image here shows a typical modern coil-over-oil unit. This is an all-in-one system that carries both the spring and the shock absorber. The type illustrated here is more likely to be an aftermarket item - it's unlikely you'd get this level of adjustment on your regular passenger car. The adjustable spring plate can be used to make the springs stiffer and looser, whilst the adjustable damping valve can be used to adjust the rebound damping of the shocks. More sophisticated units have adjustable compression damping as well as a remote reservoir. Whilst you don't typically get this level of engineering on car suspension, most motorbikes do have preload, rebound and spring tension adjustment. See the section later on in this page about the ins and outs of complex suspension units.
SUSPENSION BUSHES
These are the rubber grommets which separate most of the parts of your suspension from each other. They're used at the link of an A-Arm with the subframe. They're used on anti-roll bar links and mountings. They're used all over the place, and from the factory, I can almost guarantee they're made of rubber. Rubber doesn't last. It perishes in the cold and splits in the heat. Perished, split rubber was what brought the Challenger space shuttle down. This is one of those little parts which hardly anyone pays any attention to, but it's vitally important for your car's handling, as well as your own safety, that these little things are in good condition. My advice? Replace them with polyurethane or polygraphite bushes - they are hard-wearing and last a heck of a lot longer. And, if you're into presenting your car at shows, they look better than the naff little black rubber jobs. Like all suspension-related items though, bushes are a tradeoff between performance and comfort. The harder the bush compound, the less comfort in the cabin. You pays your money and makes your choice. If you have an off-road vehicle like a Jeep Wrangler, suspension bushings are an important part of your suspension system. SUSPENSION TYPES In their infinite wisdom, car manufacturers have set out to baffle us with the sheer number of different types of suspension available for both front and rear axles. The main groupings are dependent and independent suspension types but this naming convention really only applies to traditional or analogue suspension systems. Even independent systems are typically joined across the car by an anti-roll bar and so are not truly independent. From about 2006 onwards, the concept of fully independent suspension systems started to appear on cars where the anti-roll bar was replaced by sophisticated computer software connected to some form of electronically-controlled suspension. See the section later on dealing with digital suspension systems for more information. If you know of any not listed here, e-mail me and let me know - I would like this page to be as complete as possible. FRONT SUSPENSION - DEPENDENT SYSTEMS So-called because the front wheel's suspension systems are physically linked. For everyday use, they are, in a word, shite. I hate to be offensive, but they are. There is only one type of dependent system you need to know about. It is basically a solid bar under the front of the car, kept in place by leaf springs and shock absorbers. It's still common to find these on trucks, but if you find a car with one of these you should sell it to a museum. They haven't been used on mainstream cars for years for three main reasons: . Shimmy - because the wheels are physically linked, the beam can be set into oscillation if one wheel hits a bump and the other doesn't. It sets up a gyroscopic torque about the steering axis which starts to turn the axle left-to-right. Because of the axle's inertia, this in turn feeds back to amplify the original motion. . Weight - or more specifically unsprung weight. Solid front axles weigh a lot and either need sturdy, heavy leaf springs or heavy suspension linkages to keep their wheels on the road. . Alignment - simply put, you can't adjust the alignment of wheels on a rigid axis. From the factory, they're perfectly set, but if the beam gets even slightly distorted, you can't adjust the wheels to compensate. I frequently get pulled-up on the above statements from people jumping to defend solid- axle suspension. They usually send me pictures like this and claim it's the best suspension system for off-road use. I have to admit, for off-road stuff, it probably is pretty good. But let's face it; how many people with these vehicles ever go off-road? The closest they come to having maximum wheel deflection is when the mother double- parks the thing with one wheel on the kerb during the school-run......
Picture credit: Landrover Owner's Group
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FRONT SUSPENSION - INDEPENDENT SYSTEMS So-named because the front wheel's suspension systems are independent of each other (except where joined by ananti-roll bar) These came into existence around 1930 and have been in use in one form or another pretty much ever since then. MACPHERSON STRUT OR MCPHERSON STRUT This is currently, without doubt, the most widely used front suspension system in cars of European origin. It is simplicity itself. The system basically comprises of a strut-type spring and shock absorber combo, which pivots on a ball joint on the single, lower arm. At the top end there is a needle roller bearing on some more sophisticated systems. The strut itself is the load-bearing member in this assembly, with the spring and shock absorber merely performing their duty as oppose to actually holding the car up. In the picture here, you can't see the shock absorber because it is encased in the black gaiter inside the spring. The steering gear is either connected directly to the lower shock absorber housing, or to an arm from the front or back of the spindle (in this case). When you steer, it physically twists the strut and shock absorber housing (and consequently the spring) to turn the wheel. Simple. The spring is seated in a special plate at the top of the assembly which allows this twisting to take place. If the spring or this plate are worn, you'll get a loud 'clonk' on full lock as the spring frees up and jumps into place. This is sometimes confused for CV joint knock. ROVER 2000 MACPHERSON DERIVATIVE
During WWII, the British car maker Rover worked on experimental gas-turbine engines, and after the war, retained a lot of knowledge about them. The gas-turbine Rover T4, which looked a lot like the Rover P6, Rover 2000 and Rover 3500, was one of the prototypes. The chassis was fundamentally the same as the other Rovers and the net result was the the 2000 and 3500 ended up with a very odd front suspension layout. The gas turbine wasn't exactly small, and Rover needed as much room as possible in the engine bay to fit it. The suspension was derived from a normal MacPherson strut but with an added bellcrank. This allowed the suspension unit to sit horizontally along the outside of the engine bay rather than protruding into it and taking up space. The bellcrank transferred the upward forces from the suspension into rearward forces for the spring / shock combo to deal with. In the end, the gas turbine never made it into production and the Rover 2000 was fitted with a 2-litre 4-cylinder engine, whilst the Rover 3500 was fitted with an 'evergreen' 3.5litre V8. Open the hood of either of these classics and the engine looks a bit lost in there because there's so much room around it that was never utilised. The image on the left shows the Rover-derivative MacPherson strut. Potted history of MacPherson: Earle S. MacPherson of General Motors developed the MacPherson strut in 1947. GM cars were originally design-bound by accountants. If it cost too much or wasn't tried and tested, then it didn't get built/used. Major GM innovations including the MacPherson Strut suspension system sat stifled on the shelf for years because innovation cannot be proven on a spreadsheet until after the product has been produced or manufactured. Consequently, Earle MacPherson went to work for Ford UK in 1950, where Ford started using his design on the 1950 'English' Ford models straight away. Today the strut type is referred to both with and without the "a" in the name, so both McPherson Strut and MacPherson Strut can be used to describe it. Further note: Earle MacPherson should never be confused with Elle McPherson - the Australian über-babe. In her case, the McPherson Strut is something she does on a catwalk, or in your dreams if you like that sort of thing. And if you're a bloke, then you ought to.... DOUBLE WISHBONE SUSPENSION SYSTEMS. The following three examples are all variations on the same theme. COIL SPRING TYPE 1
This is a type of double-A or double wishbone suspension. The wheel spindles are supported by an upper and lower 'A' shaped arm. In this type, the lower arm carries most of the load. If you look head-on at this type of system, what you'll find is that it's a very parallelogram system that allows the spindles to travel vertically up and down. When they do this, they also have a slight side-to-side motion caused by the arc that the wishbones describe around their pivot points. This side-to-side motion is known as scrub. Unless the links are infinitely long the scrub motion is always present. There are two other types of motion of the wheel relative to the body when the suspension articulates. The first and most important is a toe angle (steer angle). The second and least important, but the one which produces most pub talk is the camber angle, or lean angle. Steer and camber are the ones which wear tyres.
COIL SPRING TYPE 2
This is also a type of double-A arm suspension although the lower arm in these systems can sometimes be replaced with a single solid arm (as in my picture). The only real difference between this and the previous system mentioned above is that the spring/shock combo is moved from between the arms to above the upper arm. This transfers the load-bearing capability of the suspension almost entirely to the upper arm and the spring mounts. The lower arm in this instance becomes a control arm. This particular type of system isn't so popular in cars as it takes up a lot room.
MULTI-LINK SUSPENSION This is the latest incarnation of the double wishbone system described above. It's currently being used in the Audi A8 and A4 amongst other cars. The basic principle of it is the same, but instead of solid upper and lower wishbones, each 'arm' of the wishbone is a separate item. These are joined at the top and bottom of the spindle thus forming the wishbone shape. The super-weird thing about this is that as the spindle turns for steering, it alters the geometry of the suspension by torquing all four suspension arms. They have complex pivot systems designed to allow this to happen. Car manufacturers claim that this system gives even better road-holding properties, because all the various joints make the suspension almost infinitely adjustable. There are a lot of variations on this theme appearing at the moment, with huge differences in the numbers and complexities of joints, numbers of arms, positioning of the parts etc. but they are all fundamentally the same. Note that in this system the spring (red) is separate from the shock absorber (yellow).
TRAILING-ARM SUSPENSION
The trailing arm system is literally that - a shaped suspension arm is joined at the front to the chassis, allowing the rear to swing up and down. Pairs of these become twin- trailing-arm systems and work on exactly the same principle as the double wishbones in the systems described above. The difference is that instead of the arms sticking out from the side of the chassis, they travel back parallel to it. This is an older system not used so much any more because of the space it takes up, but it doesn't suffer from the side-to-side scrubbing problem of double wishbone systems. If you want to know what I mean, find a VW beetle and stick your head in the front wheel arch - that's a double- trailing-arm suspension setup. Simple.
TWIN I-BEAM SUSPENSION
Used almost exclusively by Ford F-series trucks, twin I-beam suspension was introduced in 1965. This little oddity is a combination of trailing arm suspension and solid beam axle suspension. Only in this case the beam is split in two and mounted offset from the centre of the chassis, one section for each side of the suspension. The trailing arms are actually (technically) leading arms and the steering gear is mounted in front of the suspension setup. Ford claim this makes for a heavy-duty independent front suspension setup capable of handling the loads associated with their trucks. In an empty truck, however, going over a bump with twin I-beam suspension is like falling down stairs in leg irons.
MOULTON RUBBER SUSPENSION
This suspension system is based on the compression of a solid mass of rubber - red in both these images. The two types are essentially derivatives of the same design. It is named after Dr. Alex Moulton - one of the original design team on the Mini, and the engineer who designed its suspension system in 1959. This system is known by a few different names including cone and trumpet suspension (due to the shape of the rubber bung shown in the right hand picture). The rear suspension system on the original Mini also used Moulton's rubber suspension system, but laid out horizontally rather than vertically, to save space again. The Mini was originally intended to have Moulton's fluid- filled Hydrolastic suspension, but that remained on the drawing board for a few more years. Eventually, Hydrolastic was developed into Hydragas (see later on this page), and revised versions were adopted on the Mini Metro and the current MGF-sportscar. For a while, Moulton rubber suspension was used in a lot of bicycles - racing and mountain bikes. Due to the compact design and the simplicity of its operation and maintenance, it was an ideal solution, but has since been superceded by more advanced, lightweight designs. If you're interested in further reading, there's a memoir book out now about Alex Moulton and his original designs. Alex Moulton - a lifetime in engineering.
TRANSVERSE LEAF-SPRING
This system is a bit odd in that it combines independent double wishbone suspension with a leaf spring like you'd normally find on the rear suspension. Famously used on the Corvette, it involves one leaf spring mounted across the vehicle, connected at each end to the lower wishbone. The centre of the spring is connected to the front subframe in the middle of the car. There are still two shock absorbers, mounted one to each side on the lower wishbones. Chevy insist that this is the best thing since sliced bread for a suspension system but there are plenty of other experts, manufacturers and race drivers who think it's junk. It's never been clear if this was a performance and design decision or a cost issue, but this type of system is very rare.
Historically, Triumph used transverse leaf spring suspension on the front of their small chassis cars (Herald, Vitesse, Spitfire & GT6). In the good old British school of thought, they did this because it was cheap. The spring was bolted to the differential, rather than the chassis, and under (very) hard cornering you got jacking and tuck-under. If you got this whilst driving and panicked enough to let off the gas, or worse, step on the brake, you got massive over-steer, and pirouetted off into the nearest tree. There were plenty of complaints about this suspension system in the late 60's, so Triumph changed to a 'swing spring' system on some cars (no longer bolted to the diff), and what they called 'rotoflex' on the GT6. Again from the good old British school of thought, the replacement system was unnecessarily complicated and allegedly very fragile. To compound the issue, the rear suspension used a swing axle system (again - cheap, and also used by Mercedes and Tatra amongst others). The wheel's lower control arm on a swing axle system is pivoted a long way inboard - almost on the centerline of the car. There isn't an outboard pivot so the wheel is always at 90° to the control arm thus the wildly varying camber angles. You can see the 'folded in' look of the rear wheels in the photo above. Note : on rear wheel drive versions of swing-axle suspension, there was no lower control arm - the drive shaft itself was the suspension component. Photo credit : Triumph Herald Tricks & Tips There was also a rare Swedish sports car in the 1990's called JC Indigo which had transverse leaf spring as both front and rear suspension. The composite spring was derived from the Volvo 760 station wagon but Indigo used it both as rear suspension and in a modified form in the front. The car had mostly Volvo running gear but the company had no relationship to Volvo themselves. It went out of business pretty quickly and I'm not even sure if the Indigo ever reached mass production. Interesting factoid for you: Sweden has had over 120 car manufacturers. Only three remain, only two are really mass producers and it is unlikely that more than one of them will survive to see 2020. SPEAKING SPECIFICALLY ABOUT CORVETTE LEAF-SPRING SUSPENSION. The Corvette was not the first car to combine leaf springs with independent suspension. As well as the Triumph Herald, Fiat did something similar in the 50s with steel springs. The recent Volvo 960 Wagon (not sedan) also used fibreglass leaf springs in the rear with independent suspension. The Corvette is, as far as I know, the only vehicle that uses this setup both front and rear. The system is definitely independent, not like a live axle or a twist beam rear end. With dependent systems, when one wheel moves, the other is forced to move too. The design of the Corvette suspension is such that even though both sides are linked one side can move without affecting the other, hence its classification as independent. But how - what about that leaf spring? Surely if it's attached to both sides, that makes this a dependent suspension system? On the older Corvettes (C2, C3, C4 rear end) the leaf spring was rigidly clamped to the subframe in the centre. That made it act like two separate leaf springs, one for each side. As two separate leaf springs it, like a torsion bar, was simply an alternative to coil springs. When considering coil-spring type suspension, the 'third spring' is essentially forgotten - the two visible coils are considered to be the springing part of the suspension. Not so - there's the anti-roll bar too. Whilst not technically a spring, it does act as a transverse torsion bar linking both sides of the suspension together. So the way GM started using the tranverse leaf spring is actually very clever; it lets one spring act as both a traditional spring and an anti-roll. Yes - if one wheel moves, spring forces (not geometric displacements like we see with a live axle) are applied to the other wheel - however, in a car with an anti-roll bar the same thing happens (see the section on anti roll bars). The problem was that it worked well as a spring, but not so well as an anti-roll bar, so in the end GM had to add anti-roll bars too. Typically, aftermarket tuners will tear the leaf springs out and replace them with coil spring systems simply to make life easier. GM left many things on the Corvette with room for improvement. Leaf springs are not really a fundamental problem - typically the view is that Corvettes would be no better from the factory with coil springs. A traditional leaf spring live axle saves money because the cost of leaf springs is less than coils, trailing arms, pan hard rod etc. The Corvette has all the same suspension arms as a system with coil springs, so the only difference is the cost of the fibreglass leaf vs. the cost of the coil spring; leaf springs cost more than a coil so GM didn't do it to save money. It's not immediately clear then why they did it other than perhaps 'because they could'. To round off this section then, here is an excellent link talking about how this suspension works - it does a far better job than I can: Fibreglass springs REAR SUSPENSION - DEPENDENT (LINKED) SYSTEMS SOLID-AXLE, LEAF-SPRING
This system was favoured by the Americans for years because it was dead simple and cheap to build. The ride quality is decidedly questionable though. The drive axle is clamped to the leaf springs and the shock absorbers normally bolt directly to the axle. The ends of the leaf springs are attached directly to the chassis, as are the tops of the shock absorbers. Simple, not particularly elegant, but cheap. The main drawback with this arrangement is the lack of lateral location for the axle, meaning it has a lot of side- to-side slop in it. THE FUEL & ENGINE BIBLE SUCK, SQUEEZE, BANG, BLOW Not a sexual maneuver, but rather the common description for how an internal combustion engine works. The basic way all internal combustion engines work is to take a mixture of fuel and air, compress it, ignite it either with a spark plug or by self-igntion (in the case of a diesel engine), allow the explosion of combusting gasses to force the piston back down and then expel the exhaust gas. The vertical movement of the piston is converted into rotary motion in the crank via connecting rods. The crank then goes out to the gearbox via a flywheel and clutch, and the gearbox sends the rotary motion to the wheels, driving the vehicle forwards. The diagram to the left is for reference for the technical jargon that will pop out on the rest of this page. It shows an inline-4 engine with dual overhead cams. NIKOLAUS OTTO If you want to be pedantic, the suck-squeeze-bang-blow cycle of a 4 stroke engine should be called the Otto Cycle, after its inventor Nikolaus Otto. The development of the internal combustion engine is quite interesting, and rather than add even more clutter to this page, enquiring minds can read about the history of the internal combustion engine here. The rest of us will carry on.... ENGINE LAYOUTS Here are some illustrations of the most common types of cylinder layout you'll find in engines today. Singles are typically used in motorbikes, snowblowers, chainsaws etc. V- twins are also found in motorbikes. The triple is almost unique to Triumph motorbikes where they call it the Speed Triple, or the 675. Inline-fours are the mainstay of car engines, as well as being found in some motorbikes too such as the BMW K1200S. Inline fives used to be used a lot in Audis but have found a new home in current Volvos. The V5 is something you'll find in some VWs. The V6 has the benefits of being smoother than an inline-four but without the fuel economy issues of a V8. Boxer engines are found in BMW motorbikes (twins) and Porsches and Subarus (fours and sixes). You had no idea, did you?
THE DIFFERENCE BETWEEN 4 STROKE AND 2 STROKE ENGINES
First, some basic concepts. Well one basic concept really - the most common types of internal combustion engine and how they work. It's worth reading this bit first otherwise the whole section on octane later in the page will seem a bit odd. Almost every car sold today has a 4 stroke engine. So do a lot of motorbikes, lawnmowers, snowblowers and other mechanical equipment. But there are still a lot of 2 stroke engines about in smaller motorbikes, smaller lawnmowers, leaf-blowers, snowblowers and such. The difference between the two engine types is the number of times the piston moves up and down in the cylinder for a single combustion cycle. A combustion cycle is the entire process of sucking fuel and air into the piston, igniting it and expelling the exhaust. HOW 2 STROKE ENGINES WORK A 2 stroke engine is different from a 4 stroke engine in two basic ways. First, the combustion cycle is completed within a single piston stroke as oppose to two piston strokes, and second, the lubricating oil for the engine is mixed in with the petrol or fuel. In some cases, such as lawnmowers, you are expected to pre-mix the oil and petrol yourself in a container, then pour it into the fuel tank. In other cases, such as small motorbikes, the bike has a secondary oil tank that you fill with 2 stroke oil and then the engine has a small pump which mixes the oil and petrol together for you. The simplicity of a 2 stroke engine lies in the reed valve and the design of the piston itself. The picture on the right shows a 4 stroke piston (left) and a 2 stroke piston (right). The 2 stroke piston is generally taller than the 4 stroke version, and it has two slots cut into one side of it. These slots, combined with the reed valve, are what make a 2 stroke engine work the way it does. The following animation shows a 2 stroke combustion cycle. As the piston (red) reaches the top of its stroke, the spark plug ignites the fuel-air- oil mixture. The piston begins to retreat. As it does, the slots cut into the piston on the right begin to align with the bypass port in the cylinder wall (the green oblong on the right). The receding piston pressurises the crank case which forces the reed or flapper valve (purple in this animation) to close, and at the same time forces the fuel-air-oil mixture already in the crankcase out through the piston slots and into the bypass port. This effectively routes the mixture up the side of the cylinder and squirts it into the combustion chamber above the piston, forcing the exhaust gas to expel through the green exhaust port on the left. Once the piston begins to advance again, it generates a vacuum in the crank case. The reed or flapper valve is sucked open and a fresh charge of fuel-air-oil mix is sucked into the crank case. When the piston reaches the top of its travel, the spark plug ignites the mixture and the cycle begins again. . . . . 00:00 / 00:04 ......
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. . . For the same cylinder capacity, 2 stroke engines are typically more powerful than 4 stroke versions. The downside is the pollutants in the exhaust; because oil is mixed with the petrol, every 2 stroke engine expels burned oil with the exhaust. 2 stroke oils are typically designed to burn cleaner than their 4 stroke counterparts, but nevertheless, the 2 stroke engine can be a smoky beast. If, like me, you grew up somewhere in Europe where scooters were all the rage for teenagers, then the mere smell of 2 stroke exhaust can bring back fond memories. The other disadvantage of 2 stroke engines is that they are noisy compared to 4 stroke engines. Typically the noise is described as "buzzy". HOW 4 STROKE ENGINES WORK 4 stroke engines are typically much larger capacity than 2 stroke ones, and have a lot more complexity to them. Rather than relying on the simple mechanical concept of reed valves, 4 stroke engines typically have valves at the top of the combustion chamber. The simplest type has one intake and one exhaust valve. More complex engines have two of one and one of the other, or two of each. So when you see "16v" on the badge on the back of a car, it means it's a 4-cylinder engine with 4 valves per cylinder - two intake and two exhaust - thus 16 valves, or "16v". The valves are opened and closed by a rotating camshaft at the top of the engine. The camshaft is driven by either gears directly from the crank, or more commonly by a timing belt. The following animation shows a 4 stroke combustion cycle. As the piston (red) retreats on the first stroke, the intake valve (left green valve) is opened and the fuel-air mixture is sucked into the combustion chamber. The valve closes as the piston bottoms out. As the piston begins to advance, it compresses the fuel-air mix. As it reaches the top of its stroke, the spark plug ignites the fuel-air mix and it burns. The expanding gasses force the piston back down on its second stroke. At the bottom of this stroke, the exhaust valve (right green valve) opens, and as the piston advances for a second time, it forces the spent gasses out of the exhaust port. As the piston begins to retreat again, the cycle starts over, sucking a fresh charge of fuel-air mix into the combustion chamber. . . . . 00:00 / 00:04 ......
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. . . Because of the nature of 4 stroke engines, you won't often find a single-cylinder 4 stroke engine. They do exist in some off-road motorbikes but they have such a thump-thump- thump motion to them that they require some large balancing shafts or counterweights on the crank to try to make the ride smoother. They also take a little longer to start from cold because you need to crank the single piston at least twice before a combustion cycle can start. Any more than one piston and the engine gets a lot smoother, starts better, and is nowhere near as thumpy. That's one of the advantages of V-6 and V-8 engines. Apart from the increased capacity, more cylinders typically means a smoother engine because it will be more in balance. Geek trivia: Mercedes-Benz needed to increase the performance of their diesel passenger cars back in the 70's as their market share in the US was increasing. As professionals with big V-8 luxury cars were trading them in for 2.4l diesels, the demand for performance had to be addressed. Mercedes did not want to retool their 114/115 series chassis and there wasn't enough room in the engine bay for a six cylinder diesel. There was, however, room for a straight-5. Benz engineers just hung another cylinder on the back of the 4 cyl block and presto! The five cylinder engine was born. This engine acquired a lot of status among the high line car owners. When Audi introduced the C2 series cars (the 5000 in America, the 100 in Europe) in 1976, they offered a 5- cylinder petrol engine too. It was basically a 1.8 litre 4-cylinder engine with an extra cylinder. That took it up to 2.0 litres but the fifth piston made such an enormous difference to the smoothness of the engine that it was often mistaken for a V6 or V8. Why only 5 cylinders instead of going for a V6? Partly for the same rationale as Mercedes (and it was a really tight fit) but primarily because Benz had made the straight-5 configuration fashionable. A straight-5 was also more fuel-efficient than a V6. It's also worth pointing out that nowadays, both Audi and VW have V5 engines with three cylinders in one bank and two in the other. Same smoothness, better gas-mileage.
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4 STROKE DIESEL ENGINES Mechanically, 4 stroke diesel engines work identically to four-stroke petrol engines in terms of piston movement and crank rotation. (To be historically accurate, petrol engines are mechanically similar to diesel engines - diesel engines came first) It's in the combustion cycle where the differences come through. First, during the intake cycle, the engine only sucks air into the combustion chamber through the intake valve - not a fuel/air mix. Second, there is no spark plug. Diesel engines work on self-ignition, or detonation - the one thing you don't want in a petrol engine (see the section on Octane later). At the top of the compression stroke, the air is highly compressed (over 500psi), and very hot (around 700 °C - 1292°F). The fuel is injected directly into that environment and because of the heat and pressure, it spontaneously combusts (this system is known as direct-injection). This gives the characteristic knocking sound that diesel engines make, and is also why pre-igniting petrol engines are sometimes refered to as 'dieseling'. Petrol engines typically run compression rations around 10:1, with lower end engines down as low as 8:1 and sportier engines up near 12:1. Diesel engines on the other hand typically run around 14:1 compression ratio and can go up as high as 25:1. Combined with the higher energy content of diesel fuel (around 147,000 BTU per gallon versus 125,000 BTU for a gallon of petrol), this means that the typical diesel engine is also a lot more efficient than your common or garden petrol engine, hence the much higher gas- mileage ratings. Because of the design of the diesel engine, the injector is the most critical part and has been subjected to literally hundreds of variations in both design and position. It has to be able to withstand massive pressures and temperatures, yet still deliver the fuel in a fine mist. One other component that some diesel engines have is a glowplug. From cold, some lower-tech engines can't retard the ignition enough, or get the air temperature high enough on startup for the spontaneous combustion to happen. In those engines, the glowplug is literally a hot wire in the top of the cylinder designed to increase the temperature of the compressed air to the point where the fuel will combust. These engines typically have a pictograph on the dashboard that looks like a lightbulb. When starting the engine cold, you need to wait for that light to go out - basically you're waiting for the glowplugs to get up to temperature. In really old diesel designs, this could be as long as 10 seconds. Nowadays it's nearly instantaneous, or in the case of advanced ECM systems, not needed at all. 2 STROKE DIESEL ENGINES Would you believe there is such a thing as a 2 stroke diesel engine? The two-stroke cycle described above turns out to be highly beneficial for the diesel model, the major difference being the inclusion of exhaust valves at the top of the cylinder. The burn cycle works similarly too. At the top of the piston travel, the air is hot and compressed, just like in a 4 stroke diesel. And like the 4 stroke, the injector sprays fuel in at that point and it self-combusts. As the gasses expand, the piston is forced downwards and towards the bottom of its stroke, the exhaust valves on the top of the cylinder open. Because the gas is still expanding at this point, the combustion chamber empties itself through the open valves. At the very bottom of the power stroke, the piston uncovers the air intake and pressurised air fills the combustion chamber forcing the last remnants of the exhaust gas out. As the piston begins its compression stroke, the exhaust valves close and the air is compressed and voila - a two-stroke diesel engine. The other difference between a 4 stroke and 2 stroke diesel engine is that the 2 stroke variety must have a turbocharger or supercharger; you'll notice I mentioned the air intake fills the cylinder with pressurised air. That doesn't happen by magic. As with 2 stroke petrol engines, every downward piston stroke is a power stroke, meaning the 2 stroke engine has the potential to product twice as much power as its 4 stroke sibling. Typically you'll find 2 stroke diesels in maritime engines (like those on freighters, tankers and cruise ships) and diesel-electric trains where more power is needed for the same size of engine. "CLEAN" DIESELS? TOYOTA'S D-CAT AND DPNR Old-school diesel engines used to sound like tractors when you started them on a cold morning, and they used to spew particulates out of the exhaust to the point where the back of the car went black. Newer generation diesels start much less noisily but for the most part still have some issues with particulates in the exhaust. Toyota claim to have solved this with their D-Cat and DPNR system. D-Cat stands for Diesel Clean Advanced Technology and DPNR stands for Diesel Particulate NOx Reduction. The operating principle is fairly sound. D-Cat is an advanced computer-controlled system for cleaning diesel exhaust gasses which relies on the DPNR catalyser. This is a combination of particle filters and normal gas-reduction catalysing metals that remove particulates, sulphur dioxide (SO2) and nitrogen dioxide (NO2) from the exhaust gasses. A sensor measures can tell when these filters are nearly full at which point a fifth diesel-injector sprays a little fuel directly into the exhaust system. Combined with the exhaust gas recirculation system, this results in all the collected pollutants being burned off, cleaning the filter in the process. DPNR requires ultra-low sulfur diesel (ULSD) to work properly. Shortly after this system was launched on the D-4D engined 2.0litre Toyota Avensis, the complaints started to come in. Notably, Dutch car magazine AutoWeek (issue 42 / 2006) exposed the problem when their DPNR-equipped Avensis started driving around with a huge cloud of white smoke pouring out of the exhaust. They weren't the only ones to have this problem. Hundreds of complaints were filed in Germany and other European countries for the same thing. The problem was that the D-Cat/DPNR system needs to 'regenerate' as described above. The particulate and gas filters are cleaned via a combustion mechanism in the exhaust, but this only happens at speeds below 160km/h (99mph), and takes about 20 minutes each time. In Germany especially, where they still have sections of unlimited-speed autobahns, people had been driving well over that speed for miles on end, then stopping and turning the car off, only to repeat the cycle twice a day during their commute. When this happens, the DPNR system never gets time to regenerate normally and the particle filters become clogged and the DPNR system forces a clean cycle to happen. This forced combustion results in white smoke as there are too many pollutants trying to be burned off at the same time. And not just a little white smoke. In the AutoWeek test, they thought their Avensis was on fire it was trailing so much smoke. Toyota promised to sort this problem out with an improved version of D-Cat fitted to the higher-spec 2.2litre engine. As of 2011 there wasn't much talk about this any more although there is still reference to the problem in a Toyota TSB (White Smoke From Exhaust, DNPR Only) INTERFERENCE VS. NON-INTERFERENCE ENGINES It's worth mentioning the two sub-types of 4 stroke engine at this point. Because the valves always open inwards, into the combustion chamber, they take up some space at the top of the chamber. In an interference engine, the position of the piston at the top of its stroke will occupy the same physical space that the open valves do whilst the piston is at the bottom of its stroke. It's important to know if your engine is an interference engine because if the timing belt breaks, at least one set of valves will stop in the open position and the momentum of the engine will ram the piston in that cylinder up into the valves requiring a very expensive engine repair or replacement. In a non- interference engine, the valves do not occupy any space that the piston could move into, so if your timing belt snaps on one of these engines, in 99% of cases you won't suffer any valve damage because the piston cannot physically touch the open valves. That is the technical explanation of why its important to get your timing belt changed at the manufacturer-specified mileage. The picture here shows the difference between the two types. On the left, circled in red is where the open valve interferes with the position of the piston at the top of its travel. On the right, a non-interference engine shows there is still a gap at the same point (exaggerated for my picture). TOP DEAD CENTRE (TDC) AND IGNITION TIMING When a piston in an engine reaches the top of its travel, that point is known as Top Dead Centre or TDC. This is important to know because I don't think any engine actually fires the spark plug with the pistons at TDC. More often than not, they fire slightly before TDC. So how does your ignition system work, and what is ignition timing all about? Well generating the spark is the easy part. The electrical system in your car supplies voltage to your coil and ignition unit. The engine will have a trigger for each cylinder, be it a mechanical trigger (points), electronic module or crank trigger. Whatever it is, at that point, the engine effectively sends a signal to the coil to discharge into the high voltage system. That charge travels into the distributor cap and is routed to the relevant spark plug where it is turned into a spark. The key to this, though, is the timing of the spark in relation to the position of the piston in the cylinder. Hence ignition timing. Having the spark ignite the fuel-air mixture too soon is basically the same as detonation and is bad for all the mechanical components of your engine. Having the spark come along too late will cause it to try to ignite the fuel-air mixture after the piston has already started to recede down the cylinder, which is inefficient and loses power. Timing the spark nowadays is usually done with the engine management system. It measures airflow, ambient temperature, takes input from knock sensors and literally dozens of sensors all over the engine. It then has an ignition timing map built into its memory and it cross references the input from all the sensors to determine the precise time that it should fire the spark plug, based on the ignition timing map. At 3000rpm, in a 4 cylinder engine, it does this about 100 times a second. In older systems, the spark timing was done using simple mechanical systems which had nowhere near the ability to compensate for the all the variables involved in a running combustion engine. Typically as an engine revs quicker, the ignition timing needs to advance because the spark needs to get to the cylinder more quickly. Why? Well the fuel-air mix takes a finite amount of time to combust. It won't burn any quicker or slower for any given engine speed. So for higher speeds, the mixture needs to be ignited earlier in the cycle to ensure that it begins to burn at the optimum timing point. In modern systems, this is all taken account of in the ignition timing map. On older mechanical system, they used mechanical or vacuum advance systems, so that the difference in the amount of vacuum generated in the intake manifold, determined the advance/retard amount of the timing. CHECKING IGNITION TIMING Despite the speed that an engine turns, it is possible for mere mortals like you and me to be able to check the ignition timing or an engine using (and you'd have never guessed this) an ignition timing light. Timing lights are typically strobe lights. They work by being connected to the battery directly and then having an induction coil clamped around one of the spark plug leads - normally the first or last cylinder in the engine depending on the manufacturer. When the engine fires the spark plug for that cylinder, the inductive loop detects the current in the wire and flashes the strobe in the timing light once. So if the engine is ticking over at 1100rpm, the strobe will flash 550 times a minute (4 stroke engine, remember?). Fantastic. So you're now holding a portable rave lighting rig but how does this help you see the timing of an engine? Well it's simple. You must have seen strobe lights working somewhere - a rave, a stage show - they're used to effectively freeze the position of something in time and space by illuminating it only at a certain point and for a fraction of a second. Shooting a strobe at someone walking in a dark room will result in you seeing them walk as if they were a flip-book animation on a reel of film. This effect is what's used to visualise the timing of your engine. Somewhere on the front of the engine there will be a notch near one of the timing belt pulleys and stamped into the metal next to it will be timing marks in degrees. On the pulley itself there will be a bump, recess or white-painted blob. When you point the timing light down towards the timing belt pulley, remember it fires once for each firing of the cylinders? Each time it fires, the white blob on the pulley should be at the same position in its rotation - the strobe fires once for each ignition spark at which point the mark should be in the same place, and the effect to you is that the whole pulley, timing mark and all, are now standing still in the strobe light. The mark on the pulley will line up with one of the degree marks stamped on the engine, so for example if the white dot always aligns with the 10° mark, it means your engine is firing at 10 degrees before TDC. When you rev the engine, the timing will change so the mark will move closer or further away from the TDC mark depending on how fast the engine is spinning. Note that in some engines, the two marks are simply painted or stamped, and there are no degree markings. In this case, the marks align when the first piston is exactly at TDC. CHECK THE TIMING MARKS FIRST After all that, it's worth pointing out that crank timing marks can be way off so it's worth confirming that your TDC marker is actually TDC before pratting about with the timing. It's not as bad now as it used to be, but in the bad old days, Rover V8's were particularly bad for this, with some being as much as 12° off! So how you do confirm your TDC really is TDC? Small cameras, a good set of feeler gauges, some cash and someone who knows what they're doing. TIMING MARKS ON CAM BELT PULLEYS The same timing marks exist stamped into the metal near, and on the pulley on the end the cam. Essentially these marks are used to line up the cam to the correct position when you're changing the timing belt. You have to make sure the engine is rotated to TDC and that the cams are properly aligned too. If you don't, the cams will spin permanently out-of-synch with the engine crank and the engine will run badly, if at all. SPARK PLUGS And engine without a spark plug is useless, unless it's a diesel engine in which case it uses a glowplug instead. But we're talking about regular petrol engines here so the next topic to get to grips with is the spark plug. It does exactly what it says on the tin - it's a plug that generates a spark. Duh. So why spend time talking about it? Well with apologies to George Orwell not all spark plugs are created equal. Some are more equal than others. They'll all do the job but the more you pay, the better the plug. All spark plugs share the same basic design and construction though. The high voltage from your vehicle's high-tension electrical system is fed into the terminal at the top of the spark plug. It travels down through the core of the plug (normally via some noise-suppression components to prevent electrical noise) and arrives at the centre electrode at the bottom where it jumps to the ground electrode creating a spark. The crush washer is designed to be crushed by tightening the spark plug down when it's screwed into the cylinder head, and as such, it helps keep the screw threads under tension to stop the spark plug from shaking loose or backing out. The insulator basically keeps the high-tension charge away from the cylinder head so that the spark plug doesn't ground before it gets a chance to generate the spark. The type of plug I've illustrated here is known as a projected nose type plug, because the tip extends below the bottom of the spark plug itself. The other main type of spark plug has the centre electrode recessed into the plug itself and merely grounds to the collar at the bottom. The advantage of the projected nose type is that the spark is better exposed to the fuel-air mixture.
Ground electrode (ground strap) types.There are plenty of different types of grounding electrodes kicking around in spark plug designs nowadays, from 'Y' shaped electrodes (like SplitFire plugs) to grooved electrodes like you'll find on Champion plugs all the way up to triple-electrode plugs like the high-end Bosch items. They're all designed to try to get a better spark, and to that end, you'll now find all sorts of exotic materials turning up too. Titanium plugs, for example, have better electrical conductivity than brass and steel plugs, and the theory is that they'll generate a stronger, more reliable spark. Gapping a spark plug. Gapping a spark plug is the process of ensuring the gap between the two electrodes is correct for the type of engine the plug is going to be used in. Too large a gap and the spark will be weak. Too small and the spark might jump across the gap too early. Generally speaking, the factory-set spark plug gap is just fine, but if you're running an older engine, or a highly tuned engine, then you need to pay attention to the gap. Feeler gauges are used to measure the gap, and a gapping tool is used to bend the outer electrode so that the gap is correct. Heat ranges. Something that is often overlooked in spark plugs is their heat rating or heat range. The term "heat range" refers to the relative temperature of the tip of the spark plug when its working. The hot and cold classifications often cause confusion because a 'hot' spark plug is normally used in a 'cold' (low horsepower) engine and vice versa. The term actually refers to the thermal characteristics of the plug itself, specifically its ability to dissipate heat into the cooling system. A cold plug can get rid of heat very quickly and should be used in engines that run hot and lean. A hot plug takes longer to cool down and should be used in lower compression engines where heat needs to be retained to prevent combustion byproduct buildup.
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HOW DOES THE FUEL-AIR MIX HAPPEN? MAGIC? You keep seeing me talk about fuel-air mix or fuel-air charge on this page, but I thought it wise to explain how this happens because it is pretty fundamental to the operation of internal combustion engines. The fuel and air are mixed in one of two main ways. The old-school method is to use a carburetor, whilst the new-tech approach is to use fuel injectors. The basic purpose is the same though, and that is to mix the fuel and air together in proportions that keep the engine running. Too little fuel and the engine runs 'lean' which makes it run hot. Too much fuel and it runs 'rich' which conversely makes the engine run cooler. Running rich can also result in fouled up spark plugs, flooded engines and stalling, not to mention wasting fuel. Finding the right balance normally involves about 10 milligrams of petrol for each combustion stroke. CARBURETORS Advantages : analogue and very predictable fuelling behaviour, simple and inexpensive to build and maintain. Disadvantages : carburetor icing in the venturi, imprecise fuel metering, float chambers don't work well if they're not the right way up. HOW THEY WORK.
A carburetor is basically a shaped tube. The shape of the tube is designed to swirl the incoming air and generate a vacuum in a section called the venturi pipe (or just the venturi). In the side of the venturi is a fuel jet which is basically a tiny hole connected to the float chamber via a pipe. It's normally made of brass and has a miniscule hole in the end of it which determines the flow of fuel through it. In more complex carburetors, this is an adjustable needle valve where a screw on the outside of the carburetor can screw a needle in and out of the valve to give some tuning control over the fuel flow. The fuel is pulled through the jet by the vacuum created in the venturi. At the bottom of the tube is a throttle plate or throttle butterfly which is basically a flat circular plate that pivots along its centreline. It is connected mechanically to the accelerator pedal or twist-grip throttle via the throttle cable. The more you push on the accelerator or twist open the throttle, the more the throttle butterfly opens. This allows more air in which creates more vacuum, which draws more fuel through the fuel jet and gives a larger fuel-air charge to the cylinder, resulting in acceleration. When the throttle is closed, the throttle butterfly in the carburetor is also closed. This means the engine is trying to suck fuel-air mix and generating a vacuum behind the butterfly valve so the regular fuel jet won't work. To allow the engine to idle without shutting off completely, a second fuel jet known as the idle valve is screwed into the venturi downwind of the throttle butterfly. This allows just enough fuel to get into the cylinders to keep the engine ticking over. FLOAT AND DIAPHRAGM CHAMBERS. To make sure a carburetor has a good, constant supply of fuel to be sucked through the fuel jets, it has a float chamber or float bowl. This is a reservoir of petrol that is constantly topped up from the fuel tank. Petrol goes through an inline filter and a strainer to make sure it's clean of contaminants and is then deposited into the float chamber. A sealed plastic box is pivotted at one end and floats on top of the fuel. Believe it or not, this is called the float. A simple lever connects to the float and controls a valve on the fuel intake line. As the fuel drops in the float chamber, the float drops with it which opens the valve and allows more fuel in. As the level goes up, the float goes up and the valve is restricted. This means that the level in the float chamber is kept constant no matter how much fuel the carburetor is demanding through the fuel jets. The quicker the level tries to drop, the more the intake valve is opened and the more petrol comes in to keep the fuel level up. This is why carburetors don't work too well when they're tipped over - the float chamber leaks or empties out resulting in a fuel spill - something you don't get with injectors. To combat this, another type of chamber is used where carburetors can't be guaranteed to be upright (like in chainsaws). These use diaphragm chambers instead. The principle is more or less the same though. The chamber is full of fuel and has a rubber diaphragm across the top of it with the other side exposed to ambient air pressure. As the fuel level drops in the chamber, the outside air pressure forces the diaphragm down. Because it's connected to an intake valve in the same way that the float is in a float chamber, as the diaphragm is sucked inwards, it opens the intake valve and more fuel is let in to replenish the chamber. Diaphragm chambers are normally spill-proof. CARB ICING. One of the problems with the spinning, compressing, vacuum-generating properties of the venturi is that it cools the air in the process. Whilst this is good for the engine (colder air is denser and burns better in a fuel-air mix), in humid environments, especially cool, humid environments, it can result in carburetor icing. When this happens, water vapour in the air freezes as it cools and sticks to the inside of the venturi. This can result in the opening becoming restricted or cut off completely. When carbs ice up, engines stop. In aircraft engines, there is a control in the cockpit called "carb heat" which either uses electrical heating elements to heat up the venturi to prevent icing, or reroutes hot air from around the exhausts back into the carburetor intakes. In cars, we don't have "carb heat" but instead there's normally a heat shield over the exhaust manifold connected via a pipe to a temperature-controlled valve at the air filter. When its cold, the valve is open and the air filter draws warm air from over the exhaust manifold and feeds it into the carburetor. As the temperature warms up, the valve closes and the carburetor gets cooler air because the risk of icing has reduced. The symptoms of carb icing are pretty easy to diagnose. First, your engine bogs down at high throttle then it loses power and ultimately could stall completely. You'll stop on the side of the road and wait a couple of minutes, then the engine will start and run normally. This is because with the engine off, the heat from the engine starts to warm up the carbs and melts the ice so that when you try to start it up again, everything is fine. COMPLEXITY FOR THE SAKE OF IT. As car engines evolved, carburetors had to evolve to cope with the various demands. It's not unusual to find five-circuit carburetors which have become so complex that they're a nightmare to design, build and maintain. That flies in the face of one of the carburetor's advantages, which used to be that they were simple. Why five circuits? The main circuit is the one which provides day-to-day running capability. It's augmented by accelerator and load (or enrichment) circuits which can vary the fuelling to accomodate sudden acceleration or the need for more power (like driving uphill). The accelerator circuit also adds a second butterfly valve in most cases which only opens at 70% throttle or more. Then there's the choke circuit designed to provide extra fuel with the throttles closed when the engine is cold, allowing it to start, and finally the idle circuit which does the same thing but when the engine is warm, to keep it going. On top of all of this, with the introduction of stricter emissions requirements came catalytic converters, and these expensive boxes of rare metals just don't work well unless the fuel-air ratio is very carefully controlled. And that's something carburetors just couldn't keep up with. Small wonder then that this mechanical tomfoolery gave way to fuel injection...... FUEL INJECTION Advantages : precise and variable fuel metering, better fuel efficiency and better emissions. Disadvantages : Fairly complex engineering that isn't very user-friendly. Binary on/off functionality at low throttles, which is especially noticable on motorbikes where the throttle becomes 'snatchy' and it becomes hard to ride smoothly at low speed. HOW IT WORKS.
Compared to carburettors, fuel injectors themselves are incredibly simple. They are basically electro-mechanically operated needle valves. The image on the right shows a cutaway of a representative fuel injector. When a current is passed through the injector electromagnetic coil, the valve opens and the fuel pressure forces petrol through the spray tip and out of the diffuser nozzle, atomising it as it does so. When current is removed, the combination of a spring and fuel back-pressure causes the needle valve to close. This gives an audible 'tick' noise when it happens, which is why even a quiet fuel-injected engine has a soft but rapid tick-tick-tick-tick noise as the injectors fire. This on-off cycle time is known as the pulse width and varying the pulse width determines how much fuel can flow through the injectors. When you ask for more throttle either via the accelerator pedal or twist-grip (on a motorbike) you're opening a butterfly valve similar to the one in a carburettor. This lets more air into the intake system and the position of the throttle is measured with a potentiometer. The engine control unit (ECU) gets a reading from this potentiometer and "sees" that you've opened the throttle. In response the ECU increases the injector pulse width to allow more fuel to be sprayed by the injectors. Downwind of the throttle body is a mass airflow sensor. This is normally a heated wire. The more air that flows past it, the quicker it disappates heat and the more current it needs to remain warm. The ECU can continually measure this current to determine if the fuel-air mix is correct and it can adjust the fuel flow through the injectors accordingly. On top of this, the ECU also looks at data coming from the oxygen (lambda) sensors in the exhaust. These tell the ECU how much oxygen is in the exhaust so it can automatically adjust for rich- or lean-running. DIFFERENT TYPES OF INJECTOR SYSTEMS. When fuel-injection was first introduced, it was fairly simple and used a single injector in the throttle body. Basically it was a carburettor-derivative but instead of having the induction vacuum suck fuel into the venturi, an injector forced fuel into the airflow. This was known as throttle-body fuel-injection, or single-point fuel-injection.
As engine design advanced, the single-point system was phased out and replaced with multi-point or multi-port fuel-injection. In this design, there is one injector for each cylinder, normally screwed into the intake manifold and aimed right at the intake valve. Because fuel is only sprayed when the intake valve is open, this systems provides more accurate fuel-metering and a quicker throttle response. Typically, multi-point injection systems have one more injector for cold-starting which sprays extra fuel into the intake manifold upstream of the regular injectors, to provide a richer fuel-air mix for cold starting. A coolant temperature sensor feeds information back to the ECU to determine when this extra injector should be used. As you would expect though, technology marches on with no regard to home mechanics, and the latest technology is direct injection, also known as GDI (gasoline direct injection). This is similar to multi-point injection only the injectors are moved into the combustion chambers themselves rather than the intake manifold. This is nearly identical to the direct injection system used in diesel engines. Essentially, the intake valve only allows air into the combustion chamber and the fuel is sprayed in directly through a high-pressure, heat-resistant injector. The fuel and air mix inside the combustion chamber itself due to the positions of the intake valve, injector tip and top of the piston crown. The piston crown in these engines is normally designed to create a swirling vortex to help mix the fuel and air before combustion, as well as having a cavity in it for ultra-lean-burn conditions (see picture to the left). The ECU controls the amount of fuel injected based on the airflow into the engine and demand, and will operate a direct injection engine in one of three modes: Full power mode is basically foot-to-the- floor driving. The fuel-air ratio is made richer and the injectors spray the fuel in during the piston intake stroke. In stoichiometric mode the fuel-air ratio is leaned off a little. The fuel is still sprayed in during the piston intake stroke but the burn is a lot cleaner and the ECU chooses this mode when the load on the engine is slightly higher than normal, for example during acceleration from a stop. Finally, when you're cruising with very little engine load, for example when you're on wide-open motorway with no traffic (I know that's hard to imagine when you live in England), the ECU will choose an ultra lean mode. In this mode, the fuel is injected later on in the 4 stroke cycle - as the piston is moving up its compression stroke. This forces the fuel-air charge right up next to the tip of the spark plug for the best burn conditions and the combustion itself takes place partly in the cylinder and partly in the shaped piston crown mentioned previously. ECU MAPS. The ECU receives a wide number of sensor readings from all over the engine. Built into the ECU is a fuelling and ignition map which is basically a gigantic table of numbers. It's like a lookup table that the ECU uses to determine injector pulse width, spark timing (and on some engines, the variable valve timing). So the ECU receives a set of values from all its sensors, which it then looks up in the fuelling and ignition map. At the point where all these numbers coincide, there is final number which the ECU then uses to set the injector pulse width. These are the manufacturer's "blessed" fuelling routines, and elsewhere on this page, there's a section dealing with chipping and remapping, whereby aftermarket tuners can alter these mapping tables to make the engine behave differently. VALVES AND VALVE MECHANISMS If you've got this far down the page, hopefully you understand that the valves are what let the fuel-air mixture into the cylinder, and let the exhaust out. Seems simple enough, but there are some interesting differences in the various types of valve mechanism. SPRING-RETURN VALVES.
Spring return valves are about the most commonly-used and most basic type of valvetrain in engines today. Their operation is simplicity itself and there are only really three variations of the same style. The basic premise here is that the spinning camshaft operates the valves by pushing them open, and valve return springs force them closed. The cam lobes either operate directly on the top of the valve itself, or in some cases, on a rocker arm which pivots and pushes on the top of the valve. The three variations of this type of valve-train are based on the combination of rocker arms (or not) and the position of the camshaft. The most basic type has the camshaft at the top of the engine with the cam lobes operating directly on the tops of the valves. The second more complex type still has the camshaft at the top of the engine, but the cam lobes operate rocker arms, which in turn pivot and operate on the tops of the valves. With some of these designs, the rocker arm is pivoted in the middle (as shown here) and with other designed, it's pivoted at one end and the cam lobe operates on it at the midpoint. Think of a fat bloke bouncing in the middle of a diving board whilst the tip of the board hits a swimmer on the head and you'll get the general idea. The third type which you'll find in some motorcycle engines and many boxer engines are pushrod-activated valves. The camshaft is actually directly geared off the crank at the bottom of the engine and the cam lobes push on pushrods which run up the sides of the engine. The top of the pushrod then pushes on a rocker arm, which finally pivots and operates on the top of the valve. The image here shows the three derivatives in their most basic form so you can see the differences between them. Note that the pushrod type shows the camshaft in the wrong place simply for the purpose of getting it into the image. In reality the camshaft in this system is right at the bottom of the engine near the crank. The rocker arms shown here are also called fingers, or followers depending on who you talk to. TAPPET VALVES
Tappet valves aren't really a unique type of valve but a derivative of spring-return valves. For the most part, the direct spring return valve described above wouldn't act directly on the top of the valve itself, but rather on an oil-filled tappet. The tappet is basically an upside-down bucket that covers the top of the valve stem and contains the spring. It's normally filled with oil through a small hole when the engine is pressurised. The purpose of tappets is two-fold. The oil in them helps quiet down the valvetrain noise, and the top of the tappet gives a more uniform surface for the cam lobe to work on. From a maintenance point of view, tappets are the items which wear and are a lot easier to swap out than entire valve assemblies. The image on the left shows a simple tappet valve assembly. I've rendered the tappet slightly transparent so you can see the return spring inside. DESMODROMIC VALVES Desmodromic valve systems are unique to Ducati motorbikes. From the Ducati website: The word 'desmodromic' is derived from two Greek roots, desmos (controlled, linked) and dromos (course, track). It refers to the exclusive valve control system used in Ducati engines: both valve movements (opening and closing) are 'operated." Classy, but what does it mean. Well in both the above systems, the closure mechanism on the valve relies on mechanical springs or hydraulics. There's nothing to actuallyforce the valve to close. With the Ducati Desmodromic system, the camshaft has two lobes per valve, and the only spring is there to take up the slack in the closing system. That's right; Ducati valves are forced closed by the camshaft. The marketing people will tell you it's one of the reasons Ducati motorbike engines have been able to rev much higher than their Japanese counterparts. The idea is that with springs especially, once you get to a certain speed, you're bound by the metallurgy of the spring - it can no longer expand to full length in the time between cylinder strokes and so you get 'valve float' where the valve never truly closes. With Desmodromic valves, that never happens because a second closing rocker arm hooks under the top of the valve stem and jams it upwards to force the valve closed. In fact, the stroke length, rods, and pistons all play their part in valve timing and maximum engine speed - it's not just the springs and valve float. This is why F1 cars use such a small stroke and pneumatic valves springs. In truth, both systems, spring or Desmodromic only work well up to a limit. Newer Japanese bikes have engines that can rev to the same limit as a Ducati just using spring-return valves. You can see the basic layout of a desmodromic valve on the right. As the cam spins, the opening lobe hits the upper rocker arm which pivots and pushes the valve down and open. As the cam continues to spin, the closing lobe hits the lower rocker arm which pivots and hooks the valve back up, closing it. The red return spring is merely there to hold the valve closed for the next cycle and doesn't provide any springing force to the closing mechanism. This is a fairly simple layout for the purposes of illustration. The real engines have Desmo-due and Desmo-quattro valve systems in them where pairs of valves are opened and closed together via the same mechanism. QUATTROVALVOLE, 16V AND THE OTHER MONIKERS YOU'LL FIND ON THE BACK OF A CAR. In the 80's, the buzzword was 16-valve. If you had a 16-valve engine you were happening. You were the dogs bollocks, the cat's meouw. In Italy, your engine was a quattrovalvole. So what the heck does all this mean? Well it's really, really simple. "Traditional" 4-cylinder in-line engines have two valves per cylinder - one intake and one exhaust. In a 16V engine, you have four per cylinder - two intake and two exhaust. (4 valves) x (4 cylinders) = 16 valves, or 16V. It follows that a 20V engine has 20 valves - 5 per cylinder. Normally three intake and two exhaust. Unless you've got a 5-cylinder Audi or Volvo in which case you've still got 4 valves per cylinder. If you're in America, the thing to have now is 32V - a 32 valve engine. Basically it's a V-8 with 4 valves per cylinder. See - it's all just basic maths. And what do all these extra valves get you apart from a lot more damage if they ever go wrong? A better breathing engine. More fuel-air mix in, quicker exhaust. When you get further down the page (and if your wife / husband hasn't come and complained to you about spending so damn long reading this stuff so late at night), you'll find some more information on why this is A Good Thing. VARIABLE VALVE TIMING An interesting topic which is useless without illustration, so instead of bogging this page down even more, Variable Valve Timing has it's own page. ROTARY / WANKEL ENGINES So you've got this far down the page and realised how ridiculously complicated traditional 2 stroke and 4 stroke engines are. The pistons, connecting rods and crank are all there to turn up-down motion into spinning motion. Then there's the complexity of valves and valve trains, timing belts, tappets, springs, fuel delivery systems etc.etc. There is a simpler way. Would you believe the rotary engine essentially has only three moving parts? Conceived in 1957 by Dr. Felix Wankel, the rotary engine (also known as the Wankel Engine or Wankel Motor) works on a very simple principle. The piston isn't a piston at all, but a three-sided convex rotor. The rendering to the right shows a typical example. When spun around a fixed pinion gear inside an epitrochoidal-shaped chamber, the spinning of the rotor creates the suck-squeeze-bang-blow cycle simply by the its position relative to the sides of the chamber. (If you ever used a Spirograph as a kid, you'll have drawn trochoidal shapes without really knowing it). Basically, the combination of the rotor and chamber shapes ensures that the three apexes of the rotor are always in contact with the chamber walls whilst at the same time always creating three different volumes. As the rotor spins, each volume gets larger and smaller in turn, creating the compression and expansion volumes required for the engine to work. But how does the spinning rotor connect to the output shaft? There's an eccentric wheel that sits in a bearing inside the rotor. The spinning rotor transfers its motion to the eccentric wheel and the centre of that wheel is connected to a crank on the output shaft. A single Wankel rotor could therefore be considered to be the equivalent of three pistons in a regular 4 stroke engine. The image below shows a single chamber of a typical rotary engine. Most rotary engines use two chambers and thus two rotors. Hence the three moving parts - the two rotors and the one output shaft. You can see there are no valves required - the intake and exhaust ports are simple openings in the combustion chamber that are covered and uncovered in the correct sequence by the spinning of the rotor. At this point you're now asking yourself two questions. The first is this - "If this is such a simple design, why doesn't everyone use it?" Well yes, the design is simple. It's also smooth. Both rotors are continuously turning in the same direction so you don't have the violent change of direction problem that a normal engine has (up/down/up/down). As well as that, the design means that the combustion cycle lasts through three quarters of each complete turn of the rotor, as compared to one quarter of every second stroke of a 4 stroke engine. But all this clever design does have some inherent problems. Rotary engines cost more to manufacture because of the engineering tolerances required to make them work. The seals at the rotor apexes have to be very finely manufactured to prevent premature wear. (The apex seals are the equivalent of the piston rings in a normal engine). The low compression ratio and relatively large combustion volumes mean that Wankel engines are also typically less fuel efficient than normal engines, and a side-effect of that it is typically more difficult to get these engines to pass emissions regulations. It's not impossible though. Mazda saw the benefits of rotary engines back in 1961 and to-date have been the only manufacturer willing to spend the time, money and resources required to get a reliable, mass-producable design. Their current generation Renesis (Rotary Engine Genesis) engine powers the Mazda RX-8. Mazda have a plentiful supply of information on the history, design and implementation of their engines. Mazda rotary engines. The second question is "Can I see an animation of this pinnacle of engineering prowess?". The answer is yes because it won't make much sense otherwise. The easiest way to understand how this all works it to keep your eye on just one of the curved sides of the rotor as it spins and observe the size of the volume between it and the chamber wall. As it passes in the intake port, the volume gets larger, generating a vacuum which pulls air into the chamber. As it passes the top, fuel is injected. As it approaches the left side of the chamber, the volume gets much smaller, creating the compression. At that point, the spark plugs fire. The combustion process causes the expansion of the gas which forces the rotor to continue its motion. Again thinking of just one side of the rotor, you'll see the volume increase in size again (to accomodate the combustion). Finally the leading rotor apex uncovers the exhaust port and as the volume decreases again, the exhaust gasses are forced out. At this point, that one side of the rotor is now ready to start its combustion cycle again. The bigger picture of course is that while the side you were watching was going through its intake cycle, the second side was going through its compression cycle and the third side was going through its exhaust cycle. Hence why a single-rotor wankel engine is the equivalent of a three-cylinder four-stroke engine. During that entire cycle you'll have noticed the eccentric ring spinning in its bearing and in turn spinning the output crank.
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. . . ENGINE COOLING SYSTEMS It stands to reason that if you fill a metal engine with fuel and air hundreds of times a second and make it explode, the whole thing is going to get pretty hot. To stop it all from melting into a fused lump of steel and aluminium, all engines have some method of keeping them cool. AIR COOLING
You don't see this much on car engines at all now. The most famous cars it was used on were rear-engined boxers like the original VW Beetle, Karmann Ghia, and Porsche Roadsters. It is still used a lot on motorbike engines because it's a very simple method of cooling. For air cooling to work, you need two things - fins (lots of them) and good airflow. An air-cooled engine is normally easy to spot because of the fins built into the outside of the cylinders. The idea is simple - the fins act as heat sinks, getting hot with the engine but transferring the heat to the air as the air passes through and between them. Air-cooled engines don't work particularly well in long, hot traffic jams though, because obviously there's very little air passing over the fins. They are good in the winter when the air is coldest, but that illustrates a weak spot in the whole design. Air cooled engines can't regulate the overall temperature of the cylinder heads and engine, so the temperature tends to swing up and down depending on engine load, air temperature and forward speed. A famous problem with air-cooling is associated with V- twin motorcycles. Because the rear cylinder is tucked in the frame behind the front cylinder, its supply of cool, uninterrupted air is extremely limited and so in these designs, the rear cylinder tends to run extremely hot compared to the front. The image on the right is ©Ducati and shows the engine from the Monster 695 motorbike. It's a good example of modern air-cooled design and you can see the fins on the engine are all angled towards the direction of travel so the air can flow through them freely. OIL COOLING To some extent, all engines have oil-cooling. It's one of the functions of the engine oil - to transfer heat away from the moving parts and back to the sump where fins on the outside of the sump can help transfer that heat out into the air. But for some engines, the oil system itself is designed to be a more efficient cooling system. BMW 'R' motorbikes are known for this (their nickname is 'oilheads'). As the oil moves around the engine, at some points it's directed through cooling passageways close to the cylinder bores to pick up heat. From there it goes to an oil radiator placed out in the airflow to disperse the heat into the air before returning into the core of the engine. Actually, in the case of the 'R' motorbikes, they're air- and oil-cooled as they have the air-cooling fins on the cylinders too. For a quick primer on how the radiator itself works, read on.... WATER COOLING This is by far and away the most common method of cooling and engine down. With water cooling, a coolant mixture is pumped around pipes and passageways inside the engine separate to the oil, before passing out to a radiator. The radiator itself is made of metal, and it forces the coolant to flow through long passageways each of which have lots of metal fins attached to the outside giving a huge surface area. The coolant transfers its heat into the metal of the radiator, which in turn transfers the heat into the surround air through the fins - essentially just like the air-cooled engine fins. The coolant itself is normally a mixture of distilled water and an antifreeze component. The water needs to be distilled because if you just use tap water, all the minerals in it will deposit on the inside of the cooling system and mess it up. The antifreeze is in the mix, obviously to stop the liquid from freezing in cold weather. If it froze up, you'd have no cooling at all and the engine would overheat and weld itself together in a matter of minutes. The antifreeze mix normally also has other chemicals in it for corrosion resistance too and when mixed correctly it raises the boiling point of water, so even in the warmer months of the year, a cooling system always needs a water / antifreeze mix in it. The coolant system in a typical car is under pressure once the engine is running, as a byproduct of the water pump and the expansion that water undergoes as it heats up. Because of the coolant mixture, the water in the cooling system can get over 100°C without boiling which is why it's never a good idea to open the radiator cap immediately after you've turned the engine off. If you do, a superheated mixture of steam and coolant will spray out and you'll spend some quality time in a burns unit.
The complexities of water cooling. Water cooling is the most common method of cooling and engine down, but it's also the most complicated. For example you don't want the coolant flowing through the radiator as soon as you start the engine. If it did, the engine would take a long time to come up to operating temperature which causes issues with the emissions systems, the drivability of the engine and the comfort of the passengers. In truly cold weather, most water cooling systems are so efficient that if the coolant flowed through the radiator at startup, the engine would literally never get warm. So this is where the thermostat comes in to play. The thermostat is a small device that normally sits in the system in-line to the radiator. It is a spring-loaded valve actuated by a bimetallic spring. In layman's terms, the hotter it gets, the wider open the valve is. When you start the engine, the thermostat is cold and so it's closed. This redirects the flow of coolant back into the engine and bypasses the radiator completely but because the cabin heater radiator is on a separate circuit, the coolant is allowed to flow through it. It has a much smaller surface area and its cooling effect is nowhere near as great. This allows the engine to build up heat quite quickly. If you look at the first of the two diagrams on the right, you can see the representation of the coolant flow in a cold engine. As the coolant heats up, the thermostat begins to open and the coolant is allowed to pass out to the radiator where it dumps heat out into the air before returning to the engine block. Once the engine is fully hot, the coolant is at operating temperature and the thermostat is permanently open, redirecting almost all the coolant flow through the radiator. If you look at the second of the two diagrams on the right, you can see the representation of the coolant flow in a hot engine. It's the action of the thermostat that allows a water-cooled engine to better regulate the heat in the engine block. Unlike an air-cooled engine, the thermostat can dynamically alter the flow of coolant depending on engine load and air temperature to maintain an even temperature.
The radiator fan. In the good old days, car radiators had belt-driven fans that spun behind the radiator as fast as the engine was spinning. The fan is there to draw the warm air away from the back of the radiator to help it to work efficiently. The only problem with the old way of doing it was that the fan ran all the time the engine was running, and stopped when the engine stopped. This meant that the radiator was having air drawn through it at the same rate in freezing cold conditions as it was on a hot day, and when you parked the car, the radiator basically cooked because it had no airflow while it was cooling down. So nowadays, the radiator fan is electric and is activated by a temperature sensor in the coolant. When the temperature gets above a certain level, the fan comes on and because it's electric, this can happen even once you've stopped the engine. This is why sometimes on a hot day, you can park up, turn off, and hear the radiator fan still going. It's also the reason there are big stickers around it in the engine bay because if you park and open the hood to go and start messing with something, the fan might still come on and neatly separate you from your fingers. The cabin heater. Most water-cooled car engines actually have a second, smaller radiator that the coolant is allowed to flow through all the time for in-car heating. It's a small heat-exchanger in the air vent system. When you select warm air with the heater controls, you will either be allowing the coolant to flow through that radiator via an inline valve in the cooling system (the old way of doing it) or moving a flap to allow the warm air already coming off that radiator to mix in with the cold air from outside. It's all these combinations and permutations of plumbing in a water-cooled engine that make it so relatively complex.
No matter what type of cooling you choose for your car, it requires careful maintenance, which the confident do-it-yourselfer can accomplish at home. You will be dealing with some common hand tools and shop supplies, antifreeze, thermostat and gasket, caps for the radiator and other stuff. Let's be honest - when it comes to buying parts, we try to do it as quickly as possible. Fortunately, there are a lot of places online, where you can get all this without headache. One of them is CARiD.com, They carry the finest Performance Engine Cooling systems and parts the industry can offer: http://www.carid.com/performance-engine-cooling.html Except the wide choice of all needed parts for your Cooling system, you will be surprised with their attractive prices. OVERHEATING ON A SNOW DAY If you live anywhere where it snows a lot, you'll have seen hundreds of motorists stranded at the side of the road, hood up, with steam pouring out of their radiators on the worst weather days - when it's snowing hard. It's counterintuitive at first - surely on the coldest, snowiest day of the year, the last thing you'd need to worry about was engine cooling? Well - sort of. If you're going on a long-distance drive - hours on end on the motorway, you probably need to consider covering part of your radiator so it doesn't get too much cold air - otherwise your engine will never quite get hot. That's rare though. More common is the lazy motorist syndrome, where they'll come out to the car park, clear the snow off the driver's side of the windscreen, get in and drive. Ten minutes later, they're standing at the side of the road, freezing, in driving snow, wondering why their engine blew up. Simple. They didn't clear the snow and ice away from in front of the radiator grille on the front of their car. That large lump of snow and ice blocks the airflow to the radiator so the engine just gets hotter and hotter until eventually it overheats and blows the radiator or pressure relief valve. It's not helped by the fact that on a good snow day, you'll be stuck in 5mph traffic anyway so there's not even a chance the snow might dislodge itself. So don't be lazy - spend the extra 2 seconds to brush that stuff away from the front bumper before you get in. WHY IS GOOD ENGINE COOLING IMPORTANT? CASE STUDY : THE BMC MINI MINOR The importance of overall engine design and cooling system design and efficiency is very well illustrated by the fate that befell the original British Motor Corporation Mini Minor. The following contribution is by Rodney Brown - a reader of this site. In the Morris Mini, the water pump, fan and radiator block were mounted in the same position as they were on the same 948cc engine which was concurrently being used in the more conventional fore & aft engine layout of the Morris Minor 1000 saloon. Both cars were designed by Alec Issegonis, and this was just post-war; England was basically bust, so make do and mend was the order of the day. It took a genius like Alec to make a fore & aft power train work transversely, by folding beneath itself to fit in a very tight space. The Mini had to be kept small to keep development, production and ownership costs down. Because of all this, whilst the cooling fan and radiator were still where you would expect to find them - at one end of the block, they now closely abutted the nearside front inner wheel arch because the normally fore & aft engine was now turned 90 degrees so it faced across the car. The arch inner flitch panel had suitable slots punched in it and a close fitting cowl enclosed the fan blades on the inner face. Good radiator cooling was possible as the engine was mounted on a sub frame which also carried the suspension components, leaving only a small shock absorber to pass in front of (and obstruct) the slots. The problem was that the Mini's front grille was large - as big an area as the original radiator, but now with no radiator actually behind it - that was on the end of the engine. Without something in the way, it offered little resistence to the flow of cold air onto the engine, (now placed sideways) close behind the grille, with just enough room to take off the distributor cap. (Early on before the cap was covered by a protective boot and plug shrouds fitted, rain would drive through the grille onto the distributor and HT lead plug connections stopping the engine.) The carburettor and inlet manifold shared the space between the engine and the bulkhead with the exhaust manifold (which only just missed the bulkhead). Therefore when the car was in motion, the whole of the side of the block facing the open grille was bathed in a 30 - 60 mph icy blast whilst the opposite side was baked by convection/radiation/conduction from an ill ventilated exhaust manifold. This is where the problem lay. The side of the piston bores closest to the front of the car remained relatively stable but on the side facing the rear bulkhead, where all the heat built up, it caused the piston bores to expand. So circular piston bores were cold on one side and hot on the other causing uneven distortion. The main effect of this was a poor fit of the piston rings which increased oil consumption, and more disastrously, enabled blow-by for unburnt fuel and combustion gasses which in turn pressurised the sump and gearbox. Remember that space-saving folded design, where the gearbox was folded under the engine? You've got it: the engine oil was also the gearbox oil. The sump/gearbox was not vented initially, but like the engine block above it, was cooled by an icy blast on one side and baked on the other! The consequences for the then-current SAE30 single-weight oils were that the oil was essentially useless after 3,000 miles. This rose to 6,000 miles with the advent of the multi grade oils, and it's interesting to note that the development of these oils in England was prompted by the pressing need to solve the problems posed by the Mini. AND SO TO FUEL (OR GASOLINE OR PETROL) Petrol (or gasoline if you're American) is a distilled and refined oil product made up of hydrogen and carbons - a hydrocarbon. A long-chain hydrocarbon to be exact (so don't get it on your skin - its carcinogenic). It's designed to berelatively safe to handle, if you're careful. ie. it doesn't spontaneously combust without extreme provocation. When you have a petrol fire, it's not the petrol itself that is burning, it's the vapour, and this is the key to fueling an engine. The carburettor or fuel injectors spray petrol into an air stream. The tiny particles of petrol evaporate into a vapour extremely quickly, and combined in a cloud with the air, it becomes extremely combustible. The smaller the particles from the carburettor jet or fuel injector, the more efficiently the mixture burns. . . . . 00:00 / 01:18 ......
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. . . DETONATION, PRE-IGNITION, PINKING, PINGING AND KNOCKING. Remember I said petrol doesn't spontaneously combust? Well it can if the conditions are right, and the conditions are extreme heat and pressure - exactly the conditions you find in the combustion chamber. When this happens, it's called detonation or pre- ignition. Diesel engines rely on this process because they don't have a spark plug in the traditional sense of the word. However in petrol engines, when this happens (also known as dieseling), it's a Very Bad Thing. Engines are designed to have the fuel-air mix burn at a fixed point in the cycle, not explode randomly. Whilst it might look like an explosion, if you could film it on a super high-speed camera, you'd see the mixture actually burns up very quickly rather than exploding. The video on the right is just that - in-cylinder video of the 4 stroke combustion cycle. The intake valve is on the right, the exhaust valve on the left. Detonation, dieseling or pre-ignition are all terms for what happens when the fuel-air mix spontaneously explodes rather than burning. Normally this happens when the mixture is all fouled up, and the engine is running hot. The temperature and pressure build up too quickly in the combustion chamber and before the piston can reach the top of its travel, the mixture explodes. This explosion tries to counteract the advancing piston and puts an enormous amount of stress on the piston, the cylinder walls and the connecting rod. From the outside of the engine, you'll hear it as a knocking or pinging sound. The precise sound is very hard to describe because every engine sounds slightly different when it happens. But the best way I can describe it is a constant 'toc toc toc' type knocking sound. Video credit: Original source unknown. Video also available on YouTube and Google Video. COMPRESSION RATIO. The compression ratio of an engine is the measurement of the ratio between the combined volume of a cylinder and a combustion chamber when the piston is at the bottom of its stroke, and the same volume when the it's at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Similarly, the higher the compression ratio, the greater the liklihood of detonation. OCTANE RATINGS - HOW TO STOP DETONATION So you know that a fuel-air mix, given the right conditions, can spontaneously combust. In order to control this property, all petrols have chemicals mixed in with them to control how quickly the fuel burns. This is known as theoctane rating of the fuel. The higher the rating, the slower and more controlled the fuel burns. Put on the geek-shades for a moment and I'll explain octane in more depth. If you don't like being blinded by science, skip down a few paragraphs. For the rest of you, octane is measured relative to a mixture of isooctane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane. The octane value of a fuel used to be controlled by the amount of tetraethyl lead in it, but in the 70s and 80s when it became apparent that lead was pretty harmful, lead-free petrol appeared and other substances were introduced to control octane instead. MEASURING OCTANE - RON, MON AND THE DIFFERENCE BETWEEN AMERICA AND THE REST OF THE WORLD.
Just so you know, the octane number is actually an imprecise measure of the maximum compression ratio at which a particular fuel can be burned in an engine without detonation. There are actually two numbers - RON (Research octane number) and MON (Motor Octane Number). The RON simulates fuel performance under low severity engine operation. The MON simulates more severe operation that might be incurred at high speed or high load and can be as much as 10 points lower than the RON. In Europe, what you'll see on the petrol pumps is the RON. However, in America, what you'll see on the petrol pump is usually the "mean" octane number - notified as (R+M)/2 - the average of both the RON and MON. This is why there is an apparent discrepancy between the octane values of petrol in America versus the rest of the world. Euro95 unleaded in Europe is 95 octane but it's the equivalent of American (R+M)/2 89 octane. In America, low altitude petrol stations typically sell three grades of petrol with octane ratings of 87, 89 and 91. High altitude stations typically also sell three grades, but with lower values - 85, 87 and 89. WHAT FACTORS AFFECT DETONATION? There's a bunch of things that can affect how likely an engine is to have detonation problems. The common ones are ambient air temperature, humidity, altitude, your engine's ability to stay cool (ie. the cooling system) and spark timing. Fortunately, nowadays the engine management system of modern cars can compensate for almost all of these by advancing and retarding the ignition timing. This is where the computer slightly adjusts the point in the ignition cycle at which the spark is generated at the spark plug. With older engines that used mechanical points to send current to the spark plugs, adjusting the timing was a manual affair that involved adjusting the distributor cap orientation. Knock sensors. Most modern cars have knock sensors screwed into the engine at multiple places. These actually detect the vibration or shock caused by detonation (rather than trying to detect the sound) and can signal the engine management system to change the ignition timing to reduce or eliminate the problem. OCTANE AND ALTITUDE
The higher the altitude above sea level, the lower the octane requirement. As a general rule of thumb, for every 300m or 1000ft above sea level, the RON value can go down by about 0.5. For example an 85 octane fuel in Denver will have about the same characteristics as an 87 octane fuel on the coast in Los Angeles. As a practical example of this, I currently live in Salt Lake City which is at around 4,200ft. We travel to Las Vegas from time to time which is at around 2,000ft. Our Subaru has a minimum octane requirement of 89 at sea level - so about 87 where we live. Last time we drove to Vegas, the petrol station we stopped at had run out of 'premium' products so we had to fill up with 85 octane. This, combined with the drop in altitude caused the 'check engine' light to come on because we'd effectively taken the engine from 87 octane at altitude to the equivalent of 83 octane at altitude - way below the minimum required by our car. The graph here gives a rough idea of how the three main grades of petrol in America perform with respect to octane at altitude. OCTANE AND POWER It's a common misconception amongst car enthusiasts that higher octane = more power. This is simply not true. The myth arose because of sportier vehicles requiring higher octane fuels. Without understanding why, a certain section of the car subculture decided that this was because higher octane petrol meant higher power. The reality of the situation is a little different. Power is limited by the maximum amount of fuel-air mixture that can be jammed into the combustion chamber. Because high performance engines operate with high compression ratios they are more likely to suffer from detonation and so to compensate, they need a higher octane fuel to control the burn. So yes, sports cars do need high octane fuel, but it's not because the octane rating is somehow giving more power. It's because it's required because the engine develops more power because of its design. There is a direct correlation between the compression ratio of an engine and its fuel octane requirements. The following table is a rough guide to octane values per engine compression ratio for a carburettor engine without engine management. For modern fuel-injected cars with advanced engine management systems, these values are lowered by about 5 to 7 points. Compression ratio Octane 5:1 72 6:1 81 7:1 87 8:1 92 9:1 96 10:1 100 11:1 104 12:1 108 The exception to prove the rule. Nowadays, higher octane fuel might actually give you more power but not because of the octane rating itself. Some petrol companies use a denser blend for the higher octane products. Denser blends mean higher energy density per volume (measured in Megajoules per litre - MJ/L). For example:
BP Regular: 32.53MJ/L BP Premium: 33.08MJ/L BP Ultimate: 33.28MJ/L Do these variations in energy density mean you'll get more power out of your engine from premium blends? Yes, but not in a linear fashion - ie. if the premium product has 5% more energy density than the basic product, you won't get 5% more power out of your engine, simply because of the inefficiencies of internal combustion and thermodynamic considerations. OCTANE AND GAS MILEAGE Here's a good question : can octane affect gas mileage. The short answer is absolutely, yes it can, but not for the reasons you might think. The octane value of a fuel itself has nothing to do with how much potential energy the fuel has, or how cleanly or efficiently it burns. All it does is control the burn. However, if you're running with a petrol that isn't the octane rating recommended for your car, you could lose gas mileage. Why? Lets say your manufacturers handbook recommends that you run 87 octane fuel in your car but you fill it with 85 instead, trying to save some money on filling up. Your car will still work just fine because the engine management system will be detecting knock and retarding the ignition timing to compensate. And that's the key. By changing the ignition timing, you could be losing efficiency in the engine, which could translate into worse gas mileage. Again as a practical example, my little tale above about our trip to Vegas on low octane gas. (Whether you want to believe some bloke on the internet or not is up to you). On the low octane gas on the trip down, we could barely get 23.5mpg out of the Subaru. Once I was able to fill it up again with premium at the recommended octane rating, we got 27.9mpg on the way back. A difference of 4.4mpg over 450 miles of driving. Doing the maths, you can figure out that by skimping on the price during fill-up, you may save a little money right there and then, but it costs in the long term because you're going to be filling up more often to do the same mileage. My advice? Do what the handbook tells you. After all it's in the manufacturers better interests that you get the most performance out of your car as you can - they don't want you badmouthing them, and in this day and age of instant internet gratification, you can bad-mouth a large company very quickly and get a lot of publicity. OCTANE BOOSTERS In some extreme cases, the highest octane fuel available might not solve a knocking or detonation problem. That's normally a symptom of a deeper problem in the engine involving carbon deposits on the cylinder heads, bad spark timing, faulty engine management systems or similar. In these cases, some people choose to add octane booster to their petrol. Basically you fill the tank as normal, then put in a measured amount of octane booster and it further raises the octane level in an attempt to stop the detonation. One of the downsides of this is that it can make the engine harder to start from cold, because the octane booster has made the fuel so much less volatile that it's hard to get it to ignite on the first couple of strokes. Products like Klotz and Redex octane boosters are readily available over the counter in most auto parts stores. Octane boosters are typically used by mis-educated motorcyclists who believe the myth (explained above) that high octane = more power.
Octane boosters tested by Fifth Gear. To try to lay the myth about octane boosters giving more power to bed for once and for all, in 2007 the UK TV show Fifth Gear picked four likely candidates and subjected them to rigorous testing. They picked Nitro Hot Shot, NOS Race Only Octane Booster, Wynn's Power Booster and STP Power Booster. All four products make the usual wild claims about increased gas mileage, more bhp and so on and so forth. They took the products to Oxford Brooks University's engine testing lab. The engine was static-mounted so measurements were made at the flywheel. The throttle was computer controlled so they could reproduce the same scenario over and over again. They first did a baseline test to find out peak bhp with regular unleaded petrol. This involved various constant-throttle settings as well as acceleration and deceleration testing, and a 1-hour constant-speed run to emulate driving on a motorway in clear traffic. Each product was tested using the identical setup, with a 15 minute 'pure' petrol flush being used in between each test to ensure there was no cross-contamination. The results were interesting. Nitrox Hot Shot, NOS Race Only Octane Booster and Wynn's Octane Booster all reduced the overall power by 2bhp. STP Power Booster reduced it by 6%. Now remember this was measured at the flywheel so by the time you induce all the drag of the gearbox and driveline into that equation, you'd likely be looking at a 5% to 10% drop at the wheels. Impressive results for products that claim to increase your engine's power. In England, octane boosters are typically also sold as "lead replacements" or "4 star additive". A lot of European cars relied on the lead in 4-star petrol for the increased octane. Lower octane unleaded fuels caused a lot of problems when they first appeared, especially with cars that didn't have engine management systems. Knocking and detonation became evident in a lot of cars and for some reason French and German engines were more susceptible than most. Dumping a shot of octane booster in the tank when filling up solved the problem by raising the RON a few points to make it the equivalent of what old leaded petrol had been. Eventually, by the late 90s, most English and European petrol stations introduced LRP - lead replacement petrol, and the problem went away. Well. Sort of...... Picture credits: Halfords and Channel 5 LEAD REPLACEMENT PETROL (LRP) AND VALVE SEATS Whilst LRP solved the problem of lower octane unleaded petrol, it introduced a new problem. The lead in leaded petrol also had a secondary function and that was to lubricate the valve seats - the top of the engine block where the valves "park" when not being opened by the cams. With the advent of LRP, detonation went away but the chemicals used to increase octane didn't have any lubricating function. Some older engines started to suffer from increased wear to the valve seats, to the point where the valves could no longer properly close and seal the intake and exhaust ports. There were a couple of high profile cases before I left for America in 2001 but I've never been able to find out the end result. If you have any information on what happened in these cases, drop me a line and I'll include the info here. THE SUPERMARKET PETROL DEBATE
In England during the 90s, supermarkets started a price war with the mainstream fuel vendors by opening their own petrol stations and undercutting the Esso's and Shell's of the world by as much as 5%. People flocked to these cheap outlets without doing any proper research. There's an old saying that begins "if it's too good to be true....." In the case of supermarket petrol, there was an obvious reason why it was cheaper - it was the lower grade fuel that the mainstream outlets wouldn't take; product that had been rejected in quality control, or had less additives and detergents than what you might get from 'branded' fuel. A measurable percentage of engines started clogging up fuel lines, running badly and failing emissions tests. It was also noticed that gas mileage dropped. Eventually the supermarkets were forced to fall in line with the Big Boys, so much so that nowadays they're normally less than 1% cheaper. Skip forwards to 2005 and the first summer of high fuel prices in America. Lo and behold, supermarkets started to sprout petrol stations and a lot of people were in the same "cheap fuel" euphoria that the English were in 10 years previously. The American market did it slightly differently though. Whereas in England, they started out with utterly sub-standard petrol, in the US it is down to the additive and detergent blends (the same system used in the UK now). All petrol vendors must have product that meets the EPA minimum guidelines and typically, branded and unbranded trucks are filled from the same supply at the refinery or distribution depot. The difference is that when a truck from one of the majors fills up, they stop at the small company pump where that company's additional detergent and additive pack is added after the main fill-up. This blend of chemicals is the 'value-added' part of the premium brand offering that makes their product meet and exceed the EPA guidelines. (The act of driving the fuel truck mixes the additive pack into the petrol). I'm not entirely clear on the percentages here, but I've spoken to tanker drivers who have claimed that it's as little has half a gallon of branded additive for each 9000 gallon truck (0.0028% additive). There are other practices that vary between branded and unbranded petrol - for example many branded suppliers have dedicated tankers for each product - tankers that only ever carry petrol or only ever carry diesel. The unbranded suppliers have been known to save money by using the same tankers for both fuels, with a cursory 'rinse' between loads (resulting in slight cross-contamination). This raises an interesting question then - are you better off to go branded, or to use the cheapest stuff you can find and then every couple of months, get a bottle of Chevron Techron additive (or whatever) and run that through your car?
As a substitute for genuinely cheaper fuel, a lot of supermarket chains now offer cheaper fuel at a price. The catch is that you have to shop with them. Once you buy a certain amount of stuff from their store, they'll knock off a percentage of the price of petrol if you buy it from them. The fuel isn't the cheap and nasty sub-standard stuff of yesteryear that they used to use - it's good, mainstream product. But they can hide the price drop in the cost of the groceries and other items you buy in store. From your perspective, you save £2 a tank when filling up. From the store's perspective, you just spent £100 in shopping so giving you £2 back on your tank of gas is pocket change. In America, some of the big-box chains, like CostCo and Sam's Club do the same thing. Rather than go the "dodgy crappy petrol" route, they're offering discounted petrol for shopping in their stores, discounting the petrol by a couple of cents per gallon as long as you've bought more than $50 of products from them. FUEL FILTERS - WITHOUT THEM, ALL THIS MEANS NOTHING
As all this information about petrol and gasoline is starting to run out of your ears, it's worth bringing up the topic of fuel filters. Without fuel filters, none of this information on petrol is worth anything. Why? In an ideal world, every time you fill your tank, the petrol would come from brand new underground tanks, through brand new hoses and nozzles, down a pristeen filler tube into a brand new gas tank. However, back in the real world, that simply isn't the case. Tiny bits of metal flake off components. Things rust. Grit and grime gets into the fuel through many different sources. For the most part, this sediment settles at the bottom of the underground tanks in a petrol station, and at the bottom of the petrol tank in your car. If you're unlucky enough to fill up just after the petrol station has received a load of fuel from a tanker though, all that sediment will be nicely mixed into the petrol, and you'll get a petrol-sediment mix in your petrol tank. Similarly, if you insist on running your petrol tank down to the 'E' mark on the fuel gauge, you'll be sucking up petrol-sediment mix from the bottom of your own tank. It's a good job then that the men in lab coats decided to put in-line fuel filters in your car. These are relatively simple little devices that come in two basic flavours.
Carburettor engine fuel filters. These are the plastic in-line fuel filters. They look like a little plastic container with a wavy yellow pad in them. They're typically designed to have the fuel sucked through them via a mechanical crank-driven fuel pump up near the carburettor. In some tuner vehicles you'll find this has been replaced with a tasty little aluminium item, usually anodised in a nice colour, designed to make it nearly impossible to find.
Fuel injection filters. These are the metal cannister-type fuel filters that are normally buried under the car somewhere. They're designed to have the fuel pushed through them by an electric high-pressure fuel pump, and so the pressure in the fuel line is much higher. This is why they're made of metal. Internally, the filter material is normally finer too. WHY FILTER THE FUEL? WON'T THE DEBRIS JUST BURN? Generally speaking, unless it's metal filings, then yes, most debris that you'd find in a fuel system would burn during combustion but that's not the problem. The problem is getting the fuel into the engine in the first place. Further back up this page you (hopefully) learned about carburettors and fuel injectors. The one thing common to both is the tiny hole at the end of the line where the fuel is finally atomised into the air. A good sized grain of sand would be all it took to block that tiny hole and once that happens, it doesn't matter how clever your engine is, it won't be getting any petrol. That is why you have to filter fuel - to keep particulates from clogging areas of the fuel system vital to its operation. Most manufacturers will tell you that fuel filters are sealed-for-life, or life-time-of-the-car items. Excuse my French but that's total bollocks. In normal operating conditions, in 'first-world' countries, you should change your fuel filter every 75,000 miles (120,000km) or so. If you're into extreme motoring, like round-the-world touring, or working in 'third- world' countries, your fuel filter might need changing as much as every 5,000 miles. That's not a slur on those countries, it's just a fact that the cleanliness of petrol station holding and delivery systems isn't really a hot priority in those countries. Plus, if you're involved in that sort of driving, chances are most of your petrol will come from a rusty metal jerry can. WHY CHANGE THE FILTER? The job of an in-line fuel filter is to filter out sediment and particulates in the petrol that might otherwise cause problems further down the line in the engine. If you think about it, the average car probably has 40 to 50 litres of petrol go through the fuel filter every week. It stands to reason then that eventually the filter is going to become clogged with debris. Once your filter gets clogged, you start to get all sorts of followon problems. In carburettor cars, you'll get sporadic and weak fuel supply which will lead to a stuttering engine, or an engine that seems to have no power under acceleration. In a fuel injection system where the fuel line pressures are much greater, a clogged filter can lead to a burned out petrol pump or a blown fuel line connection on top of the fuel starvation problems. So just bear it in mind when you get to around 75,000 miles. If you're doing your own servicing, change the filter. If you're using a dealer, insist it gets changed despite their protests (and they will protest). WHERE IS MY FUEL FILTER? You might as well ask me to explain Unified Field Theory to you here. Locating the fuel filter on any vehicle is a dark art known only to the robot that put your car together. The filter can literally be anywhere in between the tank and the engine. For carburettor engines it's most likely to be in the engine bay, probably with 50cm of where the fuel line comes up from under the car, and clipped to some other tube or cable. For injection filters, it's most likely to be attached to the chassis or a suspension component underneath the car at the back axle, close to the fuel pump and petrol tank. THE 'SOCK' FILTER. More often than not, there will be a mesh 'sock' on the pickup tube inside the petrol tank itself. This is a much trickier filter to change as it's a sort of pre-filter to catch the really large stuff. For the most part, these mesh filters don't block easily - anything sucked up against them will normally wash off with the natural movement of the petrol in the tank. Where it's possible to change the external filters yourself, doing the internal one is probably a job best left to a decent mechanic. THE CARBURETTOR INTERNAL FILTER. Some carburettors have a last line of defence in the form of a metal gause filter just inside the fuel intake. If you take the fuel line off a carburettor and peer inside, that's the most likely place for this to be if there is one. It's worth knowing about this little joy because if you go to all the trouble of changing your other in-line filter(s) and still have a fuel starvation problem, it could be this last little bugger that's blocked. Now you know. Like the site? The page you're reading is free, but if you like what you see and feel you've learned something, a small donation to help pay down my car loan would be appreciated. Thank you.
E85 ETHANOL - THE MAGIC BULLET? With the spiralling cost of fuel prices, people are looking at everything to get cheaper fuel, and one of the silver bullets seems to be E85 Ethanol-blend gasoline. I say 'seems to be' because once you do some research, which is what you're doing right here by reading this, you'll learn it's not quite the magic solution everyone would have you believe.
E85 is a blend of regular unleaded petrol with between 70% and 83% ethanol depending on the geographic location and time of year. (If you must know, Google for ASTM D 5798-99). Simply blending ethanol and petrol normally results in a product with too low a vapour pressure, especially in the winter, which is why it is a process best left to people in white labcoats in refineries. It's designed for so-called Flexible Fuel vehicles, and as such has been classified by the US Department of Energy as an alternative fuel. The facts on E85 are a little hard to come by, so I've tried to collect together and put as many as I can right here so that you, dear reader, can try to cut to the chase. So what is a flexible fuel vehicle (FFV)? Well, it's a vehicle with an engine and emissions system designed to be able to run on a blend of unleaded petrol and ethanol up to a maximum of 85% ethanol. If E85 isn't available, you can run them on just plain old petrol though. If you read all the hoopla surrounding E85, you'll see this statement crop up time and time again: "It is a renewable source of energy and reduces the crude oil imports needed to fuel America's transportation system. Ethanol is a clean, environmentally friendly fuel.". Weeeeelllllll yes. But more specifically, "sort of". It's true that it is partly based on a renewable source of energy - ethanol is basically distilled corn oil (or wheat, barley, or potatoes. Brazil, the world's largest ethanol producer, makes the fuel from sugarcane), and yes, it's a cleaner and slightly more environmentally friendly fuel. There's a few 'buts' to go with all this, and they're a big 'buts' - of Jennifer Lopez proportions. First, there isn't enough farmland to grow enough corn to produce enough ethanol to meet gasoline demands, and it wouldn't be a good use of it even if there was. Second, there's a huge hidden cost in water - it takes 10 tons of water to process 1 ton of grain for ethanol [Ref: Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble by Lester R Brown. ISBN 0393328317]. Third, in 2007, in a report on the impact of biofuels, the Organization for Economic Cooperation and Development (OECD) said biofuels may "offer a cure that is worse than the disease they seek to heal"."The current push to expand the use of biofuels is creating unsustainable tensions that will disrupt markets without generating significant environmental benefits," the OECD said. "When acidification, fertiliser use, biodiversity loss and toxicity of agricultural pesticides are taken into account, the overall environmental impacts of ethanol and biodiesel can very easily exceed those of petrol and mineral diesel," it added. And finally, in bold because it's the important part of this paragraph. E85 Ethanol-blend fuel has horrible gas mileage. What does this mean to you? Well it means you'll need a lot more of it for a start. Sure it may be cheaper than regular petrol, but there's a reason - it's a terrible way to run a vehicle. Even the governments own figures back that statement up. Check out one of their lists of flexible-fueled vehicles for yourself. On average, putting E85 in a flexible fuel vehicle will return a nauseating 25% worse gas mileage. E85 doesn't burn as efficiently as regular petrol because it contains less energy per volume - 75,760btu per gallon as oppose to 115,400btu per gallon for plain old petrol. This accounts for the 30% increase in the amount of fuel required in the fuel-air mix during combustion, and the corresponding drop in gas mileage. All this comes with an average drop of only 10% in greenhouse gas emissions. If you go by historical precedent, and assume we all move to FFV's, the income from regular petrol will drop so the oil companies will simply increase the cost of E85. At that point, you're getting terrible gas mileage but paying what you used to for just plain vanilla unleaded petrol. Remember - nothing is free. Of course this doesn't need to be the case. E85's higher octane can allow the use of higher compression, more efficient engines (if optimized for use on it). Look at the race car teams - a lot of racing engines run on pure ethanol. And when engineered to take advantage of it, high-compression, high-efficiency engines can reduce the gas-mileage deficit to about 10% less than their petrol counterparts, which is much closer. But for ethanol to be successful it must be priced below petrol so that the cents per mile cost is favorable taking into account the drop in economy. BUT WHAT ABOUT BRAZIL? For a while now, Brazil (the country, not the Terry Gilliam film) has managed to be largely independent of the world's fluctuating oil prices. By law, all Brazillian petrol must be at least 25% ethanol - E25 - created from sugar-cane-fed biorefineries. By 2007, almost all cars available in Brazil ought to be able to run on 100% ethanol. (It's worth noting that Ethanol-only cars were sold in Brazil in significant numbers between 1980 and 1995). No longer dictated-to by Big Oil, the price of their E100 is relatively low and thus it offsets the lower gas-mileage quite nicely. One argument put forth in America is that using E85 will reduce the reliance on foreign imports - specifically oil. But you need to look at the whole picture. E85 comes from corn, currently a crop used to feed people. Assuming that America has enough spare capacity to farm corn for E85 for the current demand, what happens when more people start using it? You can't increase farmland, or drop production of corn for food, so the next alternative is importing it. At which point, even using E85, you become dependent on foreign imports again. Brazil doesn't have this problem because their system is in balance and so they supply themselves with enough surplus to export their product. Most likely to America. CLEAN EXHAUST - IT DEPENDS ON YOUR DEFINITION OF THE WORD "CLEAN". Something that isn't widely publicised is the difference in emissions between corn-based ethanol, as used in America, and sugar-based ethanol, as used in Brazil. We're all told that ethanol blend fuels produce cleaner exhaust and with sugar-based ethanol, that's absolutely true. Even with corn-based ethanol, the gasses measured at an emissions check are lower (about 25% less CO2), which still looks good. But there is something an ethanol E85 vehicle will produce through the exhaust that might surprise you. The exhaust gas contains acetaldehyde (CH3CHO) and lots of it, especially if the fuel source or combustion process is contaminated with water (like cold-start condensation). Acetaldehyde is a known carcinogen (source, source) and suspected neurotoxin (source), and when exposed to its vapors, you or I would likely develop irritation of the eyes, skin and the respiratory tract. In fact, Acetaldehyde is ranked as one of the most hazardous compounds (worst 10%) to ecosystems and human health. It's obvious why this isn't widely publicised, but then you might ask the question "why don't we see this in the emissions test?". Simple. The emissions test doesn't look for it. You can't detect and measure something you're not looking for. But wait - it gets better. The corn-based ethanol production process consumes more fossil fuel energy than ethanol's actual calorific value. In other words, to produce a gallon of ethanol to be used in E85, it takes more fossil fuel energy than you could simply get by putting a gallon of refined non-blend petrol in your car. And as you know, regular petrol also gives better economy. So does anyone care about this? In fact yes. The Australian government commissioned a report on this topic - you can read it for yourself here: Ethanol health impacts. The executive summary is this: ethanol does produce more of certain nasty emissions than petrol, but less of others, and that if we break everything down into dollars (the only figure the government understands) based on lost work due to illness (or death), there isn't that much difference between the two except in one area - particulate emissions (PM). PM are the nasty small pieces of carbon that can make it into your lungs, and as with smoking can (and often does) lead to cancer after a long period of time, which can then kill people. Ethanol combustion produces substantially less of this than petrol combustion (at least at 10% concentrations, and presumably more so at higher concentrations), so ends up being marginally healthier. However, it'd be healthier still to switch over to CNG, or LPG, in combination with engine improvements to make sure more of the fuel is properly combusted. Thanks to Peter K Campbell for addition info on Ethanol and health. E85 IN NON-FLEXIBLE FUEL VEHICLES Two words : rotting seals. And I'm not talking about dead sealife. E85 is pretty acidic, and stuffing it in your regular petrol-engined car will do no end of damage to it. Apart from the spark timing and the fuel-air ratio being totally different, E85 has a whopping 105 octane rating to deal with the pre-igntion problems of having 30% more fuel in the fuel-air mix during combustion. The seals and gaskets in FFVs are designed to withstand the acidic deposits that E85 generates during combustion. Generally speaking, FFVs are manufactured to eliminate all bare aluminium, rubber and magnesium parts - all items which E85 is known to rot, and all items which a normal engine has by the bucketload. Another problem with E85 is that it's electrically conductive. Regular petrol fuel pumps aren't really designed to work with a conductive fuel, so using E85 with one could result in a fuel fire where the petrol is not only the fuel for the fire, but the electrical path for the spark. FFV fuel lines aren't made of rubber, but typically stainless steel lined with plastic. So you may get cheaper petrol but you'll get worse gas-mileage and a broken car, with the possible bonus of a raging E85-fueled inferno to boot. However, there is a fly in the ointment here, and it is E10. Because of petrol company practices (see below), most fuel-injected engines designed and built since 1988 are already somewhat adapted to using ethanol, just not in the percentage you find in E85. E10: YOU'RE USING IT RIGHT NOW It's not widely known but a lot of petrol companies now blend up to 10% ethanol into their petrol products without really admitting to it, much less advertising the fact. If you've noticed your car runs somewhat less than the advertised gas mileage, that's part of the reason. Most of the gasoline in California is currently 5.7% ethanol (2% oxygen). Ethanol is blended into petrol for a variety of reasons including . as an oxygenate to reduce CO and HC emissions . an octane booster . to provide volume in place of MTBE There's nothing wrong or underhanded about this, it's just a cost effective means to legitimate ends. So if the EPA tells you you should be getting 20mpg city and you're only getting 18mpg, even driving with a feather right foot, it's not you, it's the petrol companies. 10% ethanol blend will rob you of about 5% gas mileage, and EPA figures assume a pure non-ethanol petrol. Apart from the emissions regulations, money is a factor in ethanol blending - more product that is cheaper to produce but sold for the same price. You can bet your bottom dollar (or euro) that the European refineries are doing exactly the same thing. BUT WHAT IF I DON'T WANT ETHANOL AND CRAPPY GAS MILEAGE? In America at least, you can go to pure-gas.org and lookup gas stations local to you that do not blend ethanol with their gas. Interestingly, the Shell station closest to where I live is a zero-ethanol station and it is consistently the cheapest branded petrol in my area. Make of that what you will. If you know of similar sites for other countries, drop me a line and I'll add links to them. E15: BLOCKED BY A HOUSE VOTE, BUT APPROVED BY THE EPA 15% ethanol blend is getting into corrosive territory, especially for vehicles not designed with it in mind. In February 2011, the US House overwhelmingly voted to block the sale of E15 fuel in America. Representatives voted 286 to 135 against the bill that would have allowed the EPA to issue a waiver allowing petrol stations to sell E15. The renewable fuels association criticised the decision but there was almost universal support to block it from small enthusiast groups right up to SEMA (Specialty Equipment Market Association). The argument for E15 fuel was that it would help reduce the US's dependence on foreign oil. However, plenty of representatives understood the risks of allowing fuel to go sale that would only safely work in some cars sold after 2007, as well as the further drop in fuel efficiency that comes with a 50% higher ethanol content. However in April 2012, the EPA disregarded all objections and pushed ahead to approve the use of E15 blended petrol despite admitting that it will cause problems in vehicles manufactured before 2001. (In reality, that restriction applies to any vehicle built before 2007). This will be a problem for petrol stations as they will need to provide both E10 and E15 fuel for their customers, meaning the installation and maintenance of new underground tanks and above-ground blender pumps. That will be expensive and there's a good chance that they'll either skip E15 altogether or simply stop selling E10 and screw the motoring public. The EPA's move was for sure coupled to the ending of the 30-year tax subsidy on corn- based ethanol and the cessation of tariffs on ethanol imported from Brazil. The move itself prompted many manufacturers to indicate that if you use E15 blend, it will void your factory warranty. The battle continues. TAX CREDITS, SUBSIDIES AND TARIFFS - THE REAL STORY BEHIND E85. So given the (obscured) facts about corn-based ethanol, why the big push in America to go to E85? Simple. Money. The government is offering tax credits to the big car manufacturers to produce FFVs, even if none of them ever run on E85. Similarly, tax credits are now offered to the big oil companies to product E85 ethanol blend, even if they don't actually sell it. And when they do sell it, it will make the more money because you and I will need more of it to go the same distance. Finally, corn growers receive federal subsidies for growing corn for ethanol production. Couple that with the 54¢ per gallon tariff that is currently levied on Brazillian imports, and it shows how the corn- based ethanol has cornered the American market and is keeping the cheaper, cleaner, sugar-cane ethanol at bay. WHAT'S THAT YOU SAY? YOU WANT FUEL EFFICIENCY AND LESS COST? Picture credit: Volkswagen
Well that's the conundrum isn't it? The oil and car companies aren't going to give stuff away free. So you have to choose. Do you want less cost at the point where you're putting the petrol into your car, or less cost-of-ownership? It's like comparing financial planning. If you get a flexible fuel vehicle, your immediate cost is much less - you could be spending 30% less per fill-up. But the long-term costs become negligible because of the bad gas mileage. On the other hand, if you take the long term investment point of view, you should be looking at vehicles like the VW Polo Bluemotion. It's a three- cylinder turbodiesel, which means at the point of filling it up, you'll actually be spending more than a regular petrol vehicle. But it returns 70mpg (max), so you'll be visiting the petrol station a lot less frequently. Don't understand the maths? Ok, lets lay it out. I'm going to assume plain fuel costs here, so I'm not factoring in insurance, wear and tear, initial cost of the vehicle etc. Ready? Okay, we're going to compare two vehicles. Each drives 15,000 miles a year and each has a 16 gallon fuel tank. The owners of these vehicles are Barbie and Ken, and to be suitably sexist, Barbie has a pink VW Polo and Ken has a blue Ford Crown Victoria. They both fill up when the tank gets to 3 gallons left, so they drive 13 gallons at a time. Ken 15,000 miles = 1250 gallons at 12mpg on E85. 1250 gallons = about $2300 assuming about $1.85 a gallon. Ken stops and fills up every 156 miles.
Barbie 15,000 miles = 225 gallons at 66.5mpg (split the values of 60mpg and 73mpg for city and highway) on diesel. 225 gallons = about $787 assuming about $3.50 a gallon. Barbie stops and fills up every 864 miles.
So whilst Ken pays much less each time he fills up, he's filling up nearly 6 times as often, and at the end of the year, he's spent a whopping $1500 more in fuel costs on this nice, 'clean, environmentally-friendly' E85 ethanol. Now I don't know about you, but it seems to me that the pollution from 225 gallons of diesel is going to be a whole hell of a lot less than the pollution from 1250 gallons of E85. Obviously this example is extreme, but it does use real-world facts and figures from real-world vehicles you can buy right now. I did it to illustrate how being in posession of the facts can help clear up the doublespeak and misinformation. So if you're considering an E85-fuelled vehicle, you might want to do some more homework first, because it most certainly is not the silver bullet we're all being led to believe. For more information / propaganda, go to the official E85 fuel site. LPG / LNG / AUTOGAS - LIQUID PETROLEUM GAS / LIQUID NATURAL GAS
In Europe, LPG has been an option for drivers for years. In Australia, it's been around since the 60's. In England, it's still bubbling under and in America it's virtually unheard of. So what is it? Well, put simply, it's petroleum or natural gas compressed to the point where it becomes a liquid. The liquified gas is contained in a pressure vessel inside the car somewhere - normally a tank in the boot (or trunk if you're American). There's a feed line from there to the fuel injection system or carburettor and a solenoid switch connected to a fuel-cutoff switch, both of which are controlled from a button or switch on the dashboard. In one position, the LPG line is closed and the petrol line is open and the car works just like every other car on the road. In the other position, the petrol line is cut off and the LPG line is opened up. Liquid gas under pressure shoots up the line and out of an injector nozzle either screwed into the side of the carburettor, or integrated into the fuel injection system. As the gas expands out of the nozzle it cools down and becomes a gas. The gas is highly combustible and when mixed with the air going into the engine, creates a perfectly useable fuel-air mix for the engine to run on. Simple. The gas itself is normally some derivative of butane or propane, or a combination of the two. LPG is manufactured during the process or refining crude oil, and LNG is manufactured during the refining process of extracting natural gas from the ground. Once the gas is compressed, it becomes a liquid, and this is what is carried around in the tank in the back of your car. THE PROS AND CONS OF LPG LPG is popular because for the most part, it's cheaper than petrol and it gives a pretty good gas-mileage. There are three key issues that bother most people considering LPG conversions. The first is the tank - it takes up a lot of space in your car. For some this isn't an issue, but for others, they need the space and they don't like the idea of an ugly pressure tank up on the roof of the car. The second issue is availability. On mainland Europe this isn't a problem but in most of the rest of the world, you'd be more likely to win the lottery than just stumble across an LPG filling station. The good news though is that by flicking the switch on the dashboard, you can go back to regular petrol (as long as you've got some in the tank) and keep filling up like that until you do come across another LPG station. The third issue is cost. It costs a fair amount to get an LPG conversion done. LPG is cheaper and in the long run you'll recover the costs and start saving money, but that can take 50,000km or more. Another issue which some people don't like is the idea of the pressurisation system. To fill up an LPG tank, you need to hook on a pressurised hose to a special filler cap on the outside of the car. It's easy enough to do, and it holds itself in place whilst you're refuelling, but for some, they just don't like it. The tank itself will normally be fitted with an automatic fill limiter which looks a lot like a toilet bowl float. When the tank is nearly full, the float operates a lever which severely restricts the flow of gas into the tank. This causes enough backpressure for the pump to realise that it's time to cut off the flow. HYDROGEN Hydrogen has been touted as the Next Big Thing in terms of eco-friendly fuels for our cars but is it? Hydrogen can be used either in internal-combustion form similar to burning petrol, or as a fuel source for a fuel cell that generates electricity for electric drive motors. Currently both cases are a bit sketchy for mainstream transport. Future developments will change that but why is it currently unsuitable? The two main reasons are the cost of production and the problems with storing it once refined. Hydrogen does not exist as a source of energy without refining. It needs to be extracted from something else in order to be used. This extraction process can be costly and dirty, resulting in energy losses between 15% and 50% during extraction and compression. In the case of using hydrocarbons as the source, the resulting hydrogen is more polluting than petrol or diesel once burned. The more likely method of extracting hydrogen is using water as the source and electrolysis as the method but that is both more expensive and slower. Whilst it's true that for the most part the only exhaust from a hydrogen vehicle is water, the problem is that the energy required and pollutants released during the processes described above are no more appealling than the processes used in refining petrol. To store refined hydrogen there are two options - compressed or liquified. Compressed hydrogen occupies three times the volume of petrol for the same energy. It's normally compressed to something like 12,000psi although doing so is technically difficult and consumes a considerable amount of energy. Containing that pressure in a tank is also difficult; a steel tank would weigh one hundred times the weight of the hydrogen it contained which is impractical. A carbon fibre tank will do the trick but to contain that pressure, the cost of the tank becomes prohibitive. It's also worth noting that if a 12,000psi tank of hydrogen ruptured (for example in a collision) it would release the same amount of energy as the same weight of dynamite. Liquified hydrogen, as with compressed hydrogen, also occupuies three times the volume of petrol for the same energy. (Oddly, there's more hydrogen in a gallon of petrol than in a gallon of liquid hydrogen). Unlike the compressed version, tanks to contain liquid hydrogen are considerably lighter but must be extremely well insulated or actively cooled. They're like a thermos flask inside another thermos flask so they're quite delicate. Unfortunately because of its physical properties, hydrogen is one of the hardest gasses to liquify, resulting in energy losses between 30% and 50% in the liquification process. On top of all that, hydrogen molecules are very small and can actually leak through the walls of a steel tank. Kawasaki performed an experiment in Japan where they drove a truck full of cooled hydrogen around and lost about 6% of the payload through leakage. The hydrogen industry in general reckons that an average tank will lose 5% per day through this process.
Because of all the above, the cost of the vehicles is currently prohibitive for all but the developers. In 2010 all the development vehicles were over $1,000,000 a piece. There were only 20 hydrogen fueled cars in America and even less in Europe and Asia. Arnold Schwarzenegger's Hydrogen Hummer was a one-off $1,200,000 vehicle and wasn't representative of anything a consumer could buy. Assuming you could own a hydrogen vehicle, you then face the lack of infrastructure. California's much-touted Hydrogen Highway is still a pipedream likely to be mired in government debate forever because of the cost. Getting hydrogen to the filling stations is also a problem. A typical petrol tanker can deliver 25 tons of petrol but only 400Kg of hydrogen because of the tank requirements. So a hydrogen filling station would need 15 times the number of deliveries per day to keep it in business. Consider now the commensurate cost in fuel consumed and pollution released to deliver all that hydrogen. So to the consumer, the sticker shock would be extreme. All that expense in refining, transportation and storage would be passed on to the consumer. That's assuming you could reach the filling station in the first place. Remember compressed hydrogen occupies three times the volume of petrol of the same energy, so you'd need a tank three times the size of a petrol tank to get the same range. The current demonstrator vehicles have hydrogen tanks that fill most of the trunk and a lot of the rear passenger space, and can barely squeeze out 100 miles between fill ups. The GM and Toyota hydrogen demonstrators are always trailered to their demonstrations simply because they would never get there if they were actually driven. The highest range to date from a hydrogen vehicle is BMW's hydrogen demonstrator that managed 240 miles. The fuel cells for hydrogen-electric cars are another problem yet to be overcome. Whilst they might increase the paltry range further, you need a lot of fuel cells to produce a usable amount of electricity. Stack enough together and they have the equivalent weight of the same number of batteries required to make a pure-electric vehicle but, with the overhead of the pure cost of fuel cells. The fuel cells themselves are expensive to produce and very fragile. They don't take well to bumps and jolts - the environment they'd be exposed to in a vehicle - and they require relatively large amounts of relatively rare substances like platinum to make their catalysts. Then there's that whole Hindenburg thing. Sure, the hydrogen didn't cause the fire, but it fueled it. Imagine now crashing in a vehicle with fragile fuel cells, plumbing lines and pressurised tanks full of hydrogen. The manufacturers are keen to point out that their systems are super safe which is a fair comment but what about the 1 in 1000 crash that will happen every now and then if the vehicles are delivered to the public? What about the fact that hydrogen can't just be vented to the atmosphere because it's an explosion hazard? Picture credit: BMW Press Kit THE "RUN YOUR CAR ON WATER" BRIGADE - HHO Let me start this section with the following statement: it takes more energy to get hydrogen out of water than you can ever get back by burning hydrogen in an engine. There's just no way around that— energy can't be created or destroyed, but it can be wasted, usually as heat. Getting hydrogen from electrolysis certainly does that, being only 50-80% efficient at best. Those are the laws of thermodynamics and conservation of energy, and no amount of clever marketing, lawsuits, doublespeak or clever words is going to change that. With that in mind then: You might have come across ads on the web - maybe even ones that Google have fed to this very page - claiming you can buy a kit to make your own car run on water. These kits use high school physics to do it relying on simple electrolysis - the process of using electric current to dissociate water molecules. The resulting gas is oxyhydrogen (sometimes called Brown's Gas or HHO). It's what is used in some cutting torches. With a little fuel-line plumbing and some basic handyman skills, you can fit such a device to any engine, fill the extra tank with water, and be generating hydrogen in no time. The gas is fed into the combustion chamber along with your normal fuel-air mix and sometimes you'll see better gas mileage. However, you're using a lot of electricity from the car's electrical system to generate the hydrogen, increasing the load on the alternator, meaning more drag on the engine to turn the alternator, meaning a less efficient engine. And that right there is the divisive argument that splits the car camp in half. Some people are also so convinced that the internal combustion engine is so efficient that nothing we can do that would increase power would make up for this reduction, and as such refuse to even consider the possibilities. They find it difficult to get past the losses introduced by the electrolysis of water into hydrogen as stated above. But what about the improved efficiency in the combustion of the liquid fuel this hydrogen can cause? Look back to the video at the top of this page. During combustion, the fuel burns rather than explodes in the cylinder, which means that quite a bit of the energy is releasedafter the piston has already accelerated downwards, or even when it reaches the bottom. As such, modern internal combustion engines are extremely inefficient at converting liquid fuels to usable power. This is why the introduction of a gaseous fuel with a much higher flame front (like hydrogen) can make a difference in fuel economy. Hydrogen's flame front speed is so high it effectively does explode, so the addition of just a few percent of it in the mix ensures that virtually all of the liquid fuel's energy is actually turned into power - a short, sharp "bang" (relative to the speed of the regular ignition) that pushes the piston down with great force, dramatically reducing emissions in the process. So if this glorified high school experiment really works, why hasn't it been taken up by the car manufacturers? Unfortunately you won't see this kind of radical improvement on modern vehicles (at least without substantial additional modification) due to fuel injection and the ECU. You can learn elsewhere on this page that the ECU has maps set up to ensure the car works in a certain fashion. When you introduce extra oxygen into the tailpipe (either with the hydrogen when produced by electrolysis, or because of a more efficient combustion process) the computer thinks that you're running too lean and hence increases the amount of fuel going into the vehicle - so you end up with more power, but not necessarily a better fuel consumption. For HHO systems to work in practice generally requires older carburettor engines and a serious modding of the whole electrical system (and ECU on more modern vehicles) (see chipping and remapping). In addition, an efficient hydrogen electrolysis system itself costs a few hundred dollars to construct. Naturally that means there are plenty of dodgy operators out there on the internet selling cheap systems that have little or no effect in your vehicle in the real world. For a true hydrogen generator setup, you need deep pockets. If you want to read more on this topic, there are papers available for purchase, most notably the one by researchers at a Turkish university who showed that HHO generated on-the-fly using a vehicle's own power source, improved efficiency of combustion in 4 carburettor vehicles (very important to note that point) by so much that overall fuel usage dropped by up to 40%. That paper was published in the International Journal of Hydrogen Energy in 2000 and is available here: Fuel economy improvement by on board electrolytic hydrogen production. Thanks to Peter K Campbell for pointing me in the right direction on this topic. LET THE LAWSUITS AND COMPLAINTS BEGIN.... In August 2009, the first complaint against a company promoting a consumer-level HHO system as being able to make your engine run further, cooler, and for less cost was filed and upheld in England. Their ad was deemed to be misleading on 4 counts (and it claimed that their system could turn your car into a petrol-hydrogen hybrid). The full text of the adjudication should be searchable on the ASA website: Waterboost Hydrogen Fuel System complaint. THE SLIGHTLY MORE 'OUT THERE' VERSION OF RUNNING YOUR CAR ON WATER
No article on water powered cars would be complete without mentioning Stan Meyer or any number of other people who claim to have made cars run on water alone. Stan Meyer's idea was more unique than most - rather than generating hydrogen and storing it to be burned later, he claimed his system was a water splitter that fractured water into hydrogen and oxygen instantaneously to be burned. The water never got hot and he claimed it wasn't pure electrolysis because he was using very low current. He spent a lot of time selling the idea and getting patents for a system of electronics and oscillating radio frequencies coupled to his separation chamber. It sounded too good to be true. When he started telling the press that he'd been offered $1bn by the Arabs to sit on his invention, and that he was getting 1700% more energy out than he was putting in, it looked more and more like a scam. I believe Meyer was eventually convicted of fraud for all this in 1996 and then died in mysterious circumstances in 1998. Conspiracy theorists will tell you that he was seen off by Big Oil. The problem is that you have to remember other huge 'scientific breakthroughs' in this area, like like Martin Fleischmann and Stanley Pons claiming to have solved cold fusion. Something else that seemed to be too good to be true and in the end turned out to be just that. I've got to stick to current scientific thinking on this for the time being, that being the law of conservation of energy again. Until someone can publicly demonstrate such a system that anyone can reproduce, and reproduce successfully and frequently, Meyer's water fracture device will remain a mystery. THE EBAY PROBLEM This paragraph may seem a little out of place but I have had a lot of problems with a couple of eBay members (megamanuals and lowhondaprelude) stealing my work, turning it into PDF files and selling it on eBay. Generally, idiots like this do a copy/paste job so they won't notice this paragraph here. If you're reading this and you bought this page anywhere other than from my website at www.carbibles.com, then you have a pirated, copyright-infringing copy. Please send me an email as I am building a case file against the people doing this. Go to www.carbibles.com to see the full site and find my contact details. And now, back to the meat of the subject.... GAS-MILEAGE, MPG AND WHY AMERICAN CARS CAN NEVER MATCH THE EPA ESTIMATES Gas-mileage is the quickest indicator of how efficient a car is in terms of fuel used for distance driven. Engine size and power, driving conditions, weather (wind especially) and vehicle weight all affect mpg. Measuring gas-mileage is really easy but it's surprising how many people don't know how to do it. Basically, zero your trip counter next time you fill up, then drive as normal. When you fill up again, let the petrol pump fill to the auto-cutoff point and then make a note of the trip meter reading. Gas mileage is the number of miles on your trip meter divided by the number of gallons the petrol pump put into your tank. You'd be surprised the number of people who use the manufacturer figure for the size of the tank in that calculation instead of the amount of petrol actually put in. In England and Europe, pumps deliver in litres, so in the UK it's miles-per-litre, although most advertising still uses miles per gallon. It's worth noting that an English gallon is 1.2 US gallons. So when you see a car in England that advertises 40mpg, it's the equivalent of 33mpg in the US. In the rest of Europe it's normally advertised as litres per 100 km. So for example, 28mpg (UK) is about 10litres/100km. Often this is short-handed to 1-in-10, meaning 1 litre used in 10km of driving. THE EPA The American EPA (Environmental Protection Agency) rates all cars sold in America with gas-mileage figures, advertised as EPA-rated mpg figures on the new car sticker. It's one of the things car manufacturers rely on to sell their vehicle, especially with today's high fuel prices. Not many people understand this, so I'm here to take some of that confusion away and tell you what the EPA figures really mean.
HISTORICAL CONTEXT In the windows of every new car in an American showroom you'll see an EPA information sticker, an older example of which is seen on the right (see below for the latest revisions). There's a load of technical blurb on there to advertise the vehicle, but on the older stickers there were two big numbers; the EPA-certified fuel information figures. In this case 20mpg city and 28mpg highway. So you'd see these figures and you get into your head a rough idea of how often you'd be filling up. The problem is that these were very rough estimates. In the 1980s, the EPA conducted a study on their results vs. the real world, and discovered most drivers got significantly lower mpg figures than the EPA predicted. As a result, EPA estimates on the new car labels were dropped by 10% for city and 22% for highway from their actual results. In 2006 they dropped another 8% from those figures again to try to make the numbers match more closely. Even that isn't the end of the story though. What you really need to know is how the EPA came up with their figures in the first place. Before you carry on, you might want to put down any drinks or breakables because I know what your reaction will be at the end of this. Ready? EPA TESTING PROCEDURES Congress and car company lobbyists required the EPA to measure mpg figures using the following simulated real world conditions in a lab. That's right - EPA testing happens on a dyno in a lab, not on the open road. . Average highway speed : 49mph . Maximum highway speed : 60mph . Temperature : 75°F . No rapid acceleration . No air conditioning . No passengers . No rough roads . No hills . No wind . No low tyre pressures . No ethanol in gas The first problem is the last point : no ethanol in gas. In America, it's almost impossible to buy zero-ethanol petrol - it's all E-10 (see E10 elsewhere) so you're already going to be down 5% on the EPA figures even if you could meet all the other requirements. And for the love of God, who drives like this? 49mph on the motorway? Maximum speed 60mph? Perhaps when the model-T Ford was the Big Thing, these were valid speeds, but nowadays (and by 'nowadays' I mean 'in the last 6 decades') motorway speeds are typically 70mph maxing out at 90mph (if you're in Europe anyway). What about the rest of it - no hills, no passengers, no rough roads? Have the EPA actually driven a vehicle in the real world recently? As a rough benchmark, driving at 65mph instead of 49mph will decrease mpg by 20%. Driving at 75mph will take another 25% off that. In short, you could pay very little attention to the EPA estimates because they were, for the most part, completely meaningless. Trying to give you a concise answer. They say a picture speaks a thousand words. I don't have a picture for you but I do have a table. This is a quick reference for you to show all the various figures that went into the EPA estimates, the advertising and what you should expect in the real world. It's based on the Mercedes CLK320 sticker shown above. The blue row shows what you'd see on the EPA sticker in the window of the car. The red shows the figure you'd see on TV (eternal optimism) and the green row shows what you should expect when you drove this car in the real world. City City City Highway Highway Highway Combined Low High Avg. Low High Avg. Avg. EPA LAB TEST 21.6 26.3 23.9 26.3 42.1 34.2 29 -15% (1980 correction) 18.4 25 21.7 25 35.8 30.4 26 -8% (2006 correction) 17 23 20 23 33 28 25.5 -5% (you're using E-10 petrol) 16.1 21.8 19 21.8 31.3 26.6 25.1 What you should expect 15 20 17.5 20 30 25 21.2 CONCLUSION : THE EPA NUMBERS WERE ESSENTIALLY USELESS Yes, apart from for one thing. Too many people tried to perpetuate the myth that the EPA values were intended to suggest what a driver could expect to get in the real world. As I've shown in mind-numbing detail above, this was simply not the case. Instead, they were best used as a comparison between one vehicle and another, ie if one vehicle was EPA-rated at 20mpg and another at 25mpg, then you could pretty safely conclude that the latter gets 25% better mileage than the former, and nothing else. For a good read on this subject see the Patrick Bedard column in the Feb 2006 issue of Car and Driver magazine. 2008 : THE EPA ADJUST THEIR FIGURES Skip forward to 2008 and finally the EPA changed the way they measured mpg figures. The big changes are: . The new tests start with the car at 20°F. The old tests started at 75°F. Why the change? A cold vehicle uses more energy than a warm one. Cold temperatures are especially hard on the batteries that power hybrids, so hybrid mpg ratings dropped. . The new tests use a maximum highway speed of 80mph instead of 60mph. At that speed more engine work is done to overcome drag than to actually keep the vehicle moving at speed. . The new test includes hard acceleration. The old test used gentle acceleration. This one also affects hybrids because hard acceleration relies entirely on the regular petrol engine and uses none of the electric hybrid parts. . The new test now assumes air conditioning is used 13% of the time. The old test didn't use air conditioning at all. 13% is the mean average for all major cities across all times of year for the US. But even with these new standards, the EPA test still takes no account of hills or wind. This has the effect of skewing the test in favour of larger vehicles like SUVs. If hills and wind were included, the results would be radically different - larger, heavier vehicles use more energy to travel into wind and up hills, ie. more fuel. The 2008 EPA estimates would be far more useful if they included these factors. Because they don't the overall fuel consumption figures for SUVs are lower than is realistic. For example. Assume a car gets 40mpg without the hills and wind test, and 38mpg with. Now imagine an SUV doing the same tests gets 24mpg without the hills and wind, and 19mpg with. For the sake of comparison the car's 40mpg vs. the SUV's 24mpg doesn't look as bad as the car's 38mpg vs. the SUV's 19mpg. But I digress. So what's the outcome of this? Well first of all, the new figures are definitely much closer to what you or I could get from a real car in the real world and this can only be good news. Hybrids still suffer a hit of about 30% loss of mpg for highway and 20% for city. Regular non-hybrids will drop about 12% for highway and 8% for city. So it's a lot closer to the real world than it was, but is it close enough or should we still just use the EPA figures as an arbitrary comparison of vehicle mpg as measured against an arbitrary scale? Time will tell, but it could be argued that the major car manufacturers and oil companies lobbied for this change to take the shine off hybrid vehicles - after all, they're the ones that suffer the most with the new rating. 2011: NEW EPA STICKERS WITH MORE INFORMATION
Time marches ever forwards and so do the EPA. In 2011 they introduced the latest version of their informative window stickers. In addition to the baseline mpg, they now contain further breakdowns of information such as the number of gallons per 100 miles, bringing them in-line with the sort of figures Europeans are used to seeing - litres per 100km. There's also smog and greenhouse gas ratings, again very similar to the
European ratings for grams of CO2 per km. On the right there is a 'savings' figure that compares the sticker of the car you're looking at to an 'average' car. The details of the 'average' car are stated in the white text in the black box underneath: it gets 22mpg and costs $12,600 in fuel over 5 years assuming 15,000 miles a year at $3.70/gallon for petrol. This allows you, the consumer, to do some mental maths based on fluctuations in your own mileage and the price of petrol. Finally there's a QR code that you can scan with a mobile device which will take you to a site with more information about the vehicle in question, and an annual fuel cost estimate. All in all, a nice revision to the label, designed to make it much more obvious just how much of a petrol-hog that new SUV that you're eyeing up really is. The information is far more clearly presented and there's a lot less ambiguity about "between" figures. New stickers for the latest generation of cars. In addition to the overhaul of the petrol sticker, the EPA introduced a standardised sticker for E85, diesel, LPG (CNG), hybrid, plugin hybrid, hydrogen and full electric vehicles at the same time. The full set of 2011 EPA stickers can be downloaded here as a PDF or you can see them on the EPA's fuel economy website at www.fueleconomy.gov. If you're curious about what others are getting in the real world, there's three websites that will help you out: the fueleconomy.gov site mentioned above is the US government's own website where people like you and I contribute to their real-world mileage database. GreenHybrid.com which is based more on hybrid vehicles, and TrackYourGasMileage.com. CALCULATING YOUR OWN CARBON EMISSIONS American and European cars both report gas mileage and carbon emissions in their advertising now. The same is likely true of most other countries. Calculating your own carbon emissions from a given gas mileage figure isn't particularly complicated though.
When burned, 1 US Gallon of petrol produces 8.7kg of CO2 and 1 UK Gallon of petrol produces 10.4kg of CO2. European ratings are grams per km whilst US ratings are grams per mile. So for example if a US car is rated at 26mpg:
26 miles = 1 gallon = 8.7kg of CO2 26 miles = 8700 grams
1 mile = 334 grams CO2 / mile There can be some variation in this basic calculation, for example vehicles with automatic stop-start engines (that stop when the car isn't moving, and auto-start when you take your foot off the brake (automatic) or put a foot on the clutch (manual) can have lower ratings because the engine isn't burning fuel when the car is stopped in traffic.
This explains why in many countries, the vehicle tax is levied on CO2 emissions. The more fuel-thirsty the car, the higher the emissions and thus the more tax you pay. Simple. THE TRANSATLANTIC CONUNDRUM Here's a question for you : why do identical cars, made by the same manufacturer, get less mpg in America than they do in Europe? I know a lot of you are reading this now thinking "Aha - that's because an imperial gallon is larger than a US gallon". Yes, but even adjusted for that, it's still true. Take for example the 2008 Honda Civic 1.8 i-VTEC 5-door manual. It's a good example of an average family saloon/sedan car. The trim levels are identical, as are the engine and gearbox, and power and torque figures. Oddly, the European cars weigh more for the same trim level. The following are all converted to US gallons: City Highway Combined Kerb mpg mpg mpg Peak power Peak torque weight U 140hp @ 128lb.ft @ K 28 43 36 6300rpm 4300rpm 1281kg U 140hp @ 128lb.ft @ S 26 34 29 6300rpm 4300rpm 1241kg Another example saloon / sedan car. The 2008 Volvo S40 2.4i. Again - same trim level, engine and gearbox. Once again, the European car weighs more: City Highway Combined Kerb mpg mpg mpg Peak power Peak torque weight U 170hp @ 170lb.ft @ K 20 37 28 6000rpm 4400rpm 1481kg U 168hp @ 170lb.ft @ S 20 28 24 6000rpm 4400rpm 1460kg DOING THE TEST DIFFERENTLY Typically, the EU mpg test is now also done on a rolling road and takes less than 20 minutes (1180 seconds if you must know): . Urban (city) : cold engine, accelerations, steady speeds and decelerations. The average speed is 12mph representative of city commute speeds (very harsh on mpg) and the distance is 4.5 miles. . Extra-Urban (highway) : warm engine, accelerations, steady speeds (50% of the test) and decelerations. Max speed is 75mph, average speed is 39mph, distance is 4.3 miles. So why the huge difference? You'd expect the figures to be within a couple of percent of each other, but they're clearly not. In fact with the EU cars weighing more you'd expect their figures to be worse. I've heard from engineers who work on economy testing for the major car manufacturers and the same theme always comes out - driving the same car with the same engine through the European (NEDC) and American (EPA Combo) tests can often yield as much as 20mpg difference between the cycles. Most of the difference comes from the cycle itself. The EPA cycle has much more violent accelerations, more harsh braking and is very transient, hardly any of the cycle has constant speed cruising. Some of the accelerations in the EPA cycle require near WOT (wide open throttle) on an engine with 170Nm of torque. The EU cycle on the other hand hand has extremely gentle accelerations and all the cruises are at a constant speed, naturally yielding much better mpg. There is also a different calibration between the US and EU engines and the US engines have a higher loading of precious metals in the cat to soak up more emissions, but these changes will not make a large MPG difference. There is a small amount of enrichment and ignition retard on cold start but once the cat is up to temperature, which happens quicker on the US cycle than EU, lambda 1.0 is always aimed for.
If you'd like to weigh in on this debate (ie, not Big Oil conspiracy), drop me a line. Other suggestions so far: Different Petrol Octane/Composition Good idea but the calorific value of low-octane fuel is pretty much the same as high-octane. European and Japanese cars are designed for higher-octane fuels (higher compression). Might be true but most European vehicles run Euro95 petrol, which is the equivalent of American (R+M)/2 89 octane. Plus, the engine specs are identical - same compression ratio, same torque, same horsepower. Different Oil Type/Viscosity used Different 'Map' on the ECU for different emissions laws Tyres - different rolling resistance? For my money, the best one is the different engine map in the ECU for emission laws, although emission laws are stricter in a lot of parts of Europe than they are in the US which you'd think would make the mpg figures worse. READER IDEAS The Transatlantic Conundrum has generated more buzz on my email than Lindsay Lohan getting out of a limo with no knickers on. Some of the ideas are quite sensible. Some are way out in left field. Scott Brereton emailed me with one of the more intelligible ideas: Like yourself I suspect that its related to engine maps, and I think it may be a quite subtle effect of differing emissions laws. After doing some research it turns out that in the UK emissions standards measure carbon monoxide(CO), hydrocarbons(HC) and lambda. Looking at the regulations for the US, as far as I can tell CO, HC and nitrogen oxides(NOx) are measured. Due to differing test methodologies, I can't make a direct comparison between the CO and HC figures, hence why I'm phrasing all this with lots of 'maybe's. Since NOx is formed under lean combustion conditions, it might be the case that fuel maps in the US are tuned richer than in the UK to minimise NOx production, this will lead to higher CO and HC but if we suppose that the CO and HC standards required in the US are more relaxed then those in the UK this would not be a problem. This richer fuel map might go some way to explaining the differing fuel consumption figures seen on either side of the Atlantic. Reader Blaine writes: It's based in the US EPA's pre-occupation with NOx levels. Recall that European smog police pay little attention to NOx, and concentrate on HC, CO, and CO2. Also recall that NOx formation occurs at extremely high temps (2700+ degrees?). US emissions systems use a catalyst to bring down NOx levels. The problem with this catalyst is that it doesn't work at "low" temperatures - even those typically found in exhaust systems. US emissions systems make this catalyst work by dumping raw fuel (or running an exceedingly rich mixture) into the exhaust stream, to burn in this NOx catalyst to keep it hot enough to perform the reduction reaction to eliminate/reduce NOx levels. This results in somewhat excessive fuel consumption, obviously. Tuners in the US, on OBD-II vehicles, have figured out that eliminating this fuel enrichment can result in a fairly substantial gain in fuel economy, especially when combined with fuel-map and timing tweaks designed to increase fuel economy in other circumstances. It's the "good-fast-cheap" triangle: "good, fast, cheap; pick two". Automotive engines are governed by a similar triangle: power, economy, emissions. European ECM's can pick two; American ECM's can only pick one, by federal mandate - emissions (every other consideration - power, fuel economy, driveability, etc - comes in as a distant second place). By going to a more european style of ECM mapping, American tuners can work some pretty amazing feats, and still maintaining emissions levels.
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TORQUE AND BHP There are two values that are generally published for an engine which tell you how strong the engine is, and they are torque and bhp - brake horsepower. Torque is a measure of the twisting power of the engine. Torque is directly related to acceleration; the more torque, the quicker you'll get up to speed. Horsepower is what will keep you at speed once you've accelerated and is directly related to the torque readings. So a high-torque, low-horsepower engine will accelerate well but be unable to maintain a high speed. Similarly, a low-torque, high-horsepower engine will not have much acceleration but will be able to go at a fair clout once it's going. THE DIFFERENCE BETWEEN HORSEPOWER AND BHP In England and the US, horsepower means Imperial horsepower. The technical definition of this is "the power a horse exerts in moving 550 pounds of cargo a distance of one foot in one second." This calculation can include just the horse and its own weight. Horsepower can be defined many ways. One horsepower equals 746 watts, and as such, proper SI units are normally used instead. The term horsepower is more a legacy term than anything else.
The term brake horsepower came about because of an apparatus called a water brake that can be used to measure horsepower. Today all manner of brakes are used from hydraulic to electrical. They all perform the same function though, and that is to load up the engine and measure the torque with strain gauges. BHP figures can be calculated from the measured torque values to determine the power of the engine at any given rotation. If bhp figures are published without any other data, you've got to assume they're measured at the crank. The problem is that once you add on clutches, flywheels, gears, driveshafts and all the other components between the engine and the wheels, the actual power at the wheel is often noticably less. So sometimes you'll see bhp figures noted as "at the wheel". This means the torque has been measured with the wheel being turned through all the above connections to give a more accurate power reading. In the bad old days, bhp readings would be taken with the engine running in "optimum" condition, ie. with no oil or water pumps attached, direct cold-air injection, super-cooled coolant, no exhaust back pressure or catalytic converters and so on and so forth. Fortunately today there are standards that have to be maintained. Most recently, in 2005 the SAE made some changes to the test procedures to eliminate some of the 'slop' in power measurements, and for car manufacturers to be able to make valid SAE- certified bhp claims, their tests must now be monitored by SAE representatives. The results of this change were interesting if only because the bhp values for engines changed without the engines themselves being modified. For example the Honda Element engine remained exactly the same, but its bhp rating dropped from 170bhp to 165bhp, simply because of the new procedures. It's worth pointing out that whilst the rest of the world used bhp or kW (kilowatts) to publish power figures for engines, in America they typically used to use hp(SAE) instead, meaning the rated power of the engine as installed in the vehicle, ie including all the engine components, pumps, drivetrain etc. Having said that, even today, all hp(SAE) or SAE-certified bhp figures are taken at the flywheel and thus still don't really tell you how much power is getting to the wheels. The only way to know that is to put your car on a dynomometer (a dyno) and get true at-the-wheel readings. CALCULATING HORSEPOWER AND BHP The formula to calculate bhp from a given torque reading is as follows:
Pi is obviously 3.14159, the torque value should be in pounds-feet and RPS is revolutions per second - RPM/60. So do a little elementary maths and you can massively simplify the formula down to this: The formula to calculate regular horsepower from a given torque reading is as follows:
Pi is still 3.14159, but this time the torque value should be in newton-metres. Again, simplified the formula becomes:
HORSEPOWER AND ALTITUDE A little footnote here : assuming all other factors are the same - same octane of petrol, same filters, same weight of vehicle etc., you lose about 3% of your engine's horsepower for every 300m / 1000ft above sea level that you drive. Worth knowing next time you go carving up the Stelvio Pass in Italy. At 9000ft, you're a full 27% down on engine power compared to sea level. "TUNING" YOUR ENGINE - HOW TO GET MORE POWER Not satisfied with the power your lump is giving you? There are solutions, and of course they depend almost entirely on how deep your pockets are. Almost any engine in any car can be adjusted, tweaked, modified and tuned to give more power. The more money you have to spend, the quicker your car will go. Customizing your engine helps push your vehicle beyond its limits. You need only reliable, premium quality performance parts to build a custom engine. If you’re looking for a trustworthy place to start shopping online, CARiD is that place. Don’t wait another moment and choose from the great variety of performance engine parts for cars & trucks at CARiD.com. Besides quality and reliable service, the parts are offered at fairly competitive prices. CHIPPING / REMAPPING About the simplest and easiest modification to most modern engines is called chipping. When it was first introducted, it involved removing the chip that contains the ignition map from the engine management system, and replacing it with one with a modified map. The new chip was designed for better torque, increased power, or just smoothing out flat spots in the power or torque curve of the engine. Nowadays, chipping should be more accurately referred to as Remapping. Gone are the days when you could just a whip a chip out of the ECU. That's so 90's. Today, when you cough up your hard earned cash at a tuner house, they'll plug a laptop in to your engine diagnostics port and upload new software which changes all manner of things from turbo control, fuelling maps, engine load and torque limiters all the way up to throttle-by-wire response (where applicable). They write their own software after studying (read: reverse-engineering) the car's ECU parameters using a rolling road and a laptop hooked to the diagnostics port. From there they can re-write the engine management software to do what they want rather than what the manufacturer wanted. Petrol cars respond well to remapping, but for some reason, diesels respond much better, especially VW diesels. It's not uncommon for a remapped VW ECU to generate 30% more power and torque after it's been breathed on. Add a turbo to that and you can see even wilder gains. Realistically though you ought to expect around a 5-7% increase in horsepower from a chip or remapping operation. Picture credit: Superchips Getting your car remapped will take a couple of hours if you go to a reputable tuner house. They'll pop your steed on a rolling road and hook it up to a dyno to get it right. In some cases, you can get a remapping module which sits in-line with the factory-fitted ECU, and then you can download or create your own mappings and upload them to the unit yourself. Power Commander are one of the more notable manufacturers of this sort of system, although theirs is predominantly designed for motorbikes. But how can this work? More torque and horsepower without changing anything in the engine? Well bear in mind that from the factory, most cars are sold to be more economy and comfort biased than performance biased. Most engines have a lot of slack for generating more power or torque, it's just a question of having the expertise to find it. A lot of work does go into these chips and remapping programs which is why they can cost upwards of $400 for a quality branded product. Whilst it might only be 5% by the numbers, you likely will notice some of the other effects, like smoother acceleration due to flat-spots in the torque curve being ironed out. Everyone I know who has chipped their vehicles has enjoyed the modification, and relative to what you can do to a car, it's a pretty cheap modification. Something to be aware of : chipping or remapping your car will likely void any warranty you have on it because you're messing with the onboard computer which in turn is going to adjust the running of the engine to be "different" from factory spec. And by "different", the manufacturer normally means "no warranty". Having said that, some tuner houses have perfected their software to the point where manufacturers own diagnostics computers can't tell that an engine has been remapped. In that case it becomes a moral issue for you - is it invalidating the warranty if they can't tell? FACTORY UPGRADES
Some manufacturers do bolt-on upgrades to their vehicles. For example Dodge introduced a bolt-on upgrade to their SRT-4 Neon in 2003. The kit comes with a modified engine management computer (the whole thing, not just the chip) along with high-flow fuel injectors. The nice thing about doing a factory upgrade is that you know for 100% certain that the parts are going to fit, and are going to work together with each other as well as your car. Since that original upgrade, Mopar have produced a veritable treasure trove of bolt-on upgrades for Dodge vehicles, and with most of them you can maintain some of the factory warranty. Factory upgrades are starting to include chips too now, competing with the aftermarket chipping business. That was a move to counter the warranty problems that some kits caused. Either way, factory bolt-ons are A Good Thing. If you want improved performance but are nervous about third-party products, getting something direct from Dodge, Ford, Toyota, Mazda etc. is a good way to go.
Picture credit: Dodge HIGH-FLOW FILTERS
Think of your engine as a breathing machine. It needs to breathe in fuel and air, and it needs to breath out exhaust gasses. Anything that gets in the way of that process is going to impede its ability to breathe. In reality of course, there are plenty of things in the way from air filters and flow sensors in the intake system, to catalysers and bizarre kinks and curves in the exhaust system. By eliminating or reducing these constrictions, you can allow your engine to breathe more easily. Sort of like Nyquil or NightNurse for an engine. By far the easiest and cheapest thing to start with is the air filter. From the factory, air filters are designed to be a compromise of filtering the guck out whilst letting the air through. Aftermarket manufacturers such as K&N and Jamex have been making high-flow air filters for years. The design of the filters is slightly different and they allow more air to pass through the filter whilst still stopping the majority of harmful particles. Again, like all these things, the claims of increased power can be hugely exaggerated. In truth, simply changing the air filter will probably add another 2 or 3hp to your engine. More air going in more easily means the engine management system will adjust the fuelling accordingly and you'll get a better fuel-air charge in the cylinder, resulting in a slight increase in power. Exaggerating the claims. As with most bolt-on performance parts, the box will always be optimistic with their claims of power increase. A reader sent me a link to this YouTube video testing a VW Golf Mk3, 1.8 litre engine with a stock OEM air filter versus a conical high-flow filter. The filter manufacturer makes the claim that their product will increase the power of your engine by 10%. In this particular test, the horsepower went from 91.9hp with the OEM filter up to 93.6hp with the high-flow filter - a difference of 1.7hp or 1.8%. This is basically an inconclusive result given the measurement and fault tolerance of a rolling-road dyno which is normally in the 3%-5% range. It's certainly not the 10% promised on the box and is closer the 2hp-3hp I would expect from such a filter. : High flow air filter test. COLD AIR INDUCTION (CAI) KITS
Moving on a step from simply changing the filter, you can then start looking at intake upgrade kits, also known as cold air intake or induction kits (manufactured by companies such as Injen and AEM). The basic idea with these is to make the passage from the filter to the engine less convoluted. When air is forced to go around corners, it causes turbulence which slows down the flow. By trying to make the intake pipes smoother and straighter, the idea is to give the air more chance to get to the engine and less chance of being screwed up in corners with turbulence. Cold-air kits normally remove the factory airbox from the car and poke the air intake into one of the front wings or right up front. The air in your engine bay is hot - really hot - and hot air is not conducive to good combustion. By routing the intake to somewhere where it isn't going to be sucking hot air from under the hood, you get cooler air going into your engine. Because cooler air is denser, you can get a better fuel-air charge into the cylinder than you can by simply changing the stock air filter. Cold-air intake kits can add another 3 or 4hp of raw power to the engine but more often than not, you'll notice an increase in torque lower down the rev range too. The photo to the right was snaffled from a tuning forum but it shows a nice example of a cold-air intake kit once fitted. Picture credits: K&N, AEM THROTTLE BODY HEATER BYPASS Cold air induction kits work pretty well but you need to do your homework first. A lot of cars have throttle body heaters, whereby coolant from the engine is circulated around the throttle body casing. The idea is to warm up the throttle body to prevent icing in cold weather. The problem is that these systems are hard-wired and don't take account of external air temperature, so even in the heat of summer, hot coolant is routed around the throttle body. This is a problem for CAI kits because you've gone to all the trouble of putting a nice kit in to suck cooler air into the engine, but at the final hurdle it runs through a 75°C throttle body which heats it up again, negating the whole point of the CAI kit in the first place. The solution to this is a throttle body heater bypass, which essentially involves pulling the coolant hoses off either side of the throttle body and patching them together with a length of copper pipe and two hose clamps. When you do this, the throttle body stays at ambient temperature and the CAI kit gets a chance to do its job. The only downside to this is if you live in a cold, humid climate, you might suffer from icing in the winter. But hey - if you do, reconnect the coolant hoses for the winter... HIGH-FLOW EXHAUSTS
So you've eased the flow of air into the engine, what about the exhaust? Your typical exhaust setup has kinks and bends in it to make it fit the engine compartment and under the car. In some cases these can be smoothed and straightened out somewhat but more often than not, the exhaust has to take the same route as stock. In this case, the best option is for a larger exhaust. Larger diameter exhaust pipes can accommodate more gas flowing through them and hence provide less constriction to the engine when it is blowing out exhaust gasses. Typically a factory exhaust will have two constriction points. There will likely be the catalyser at the front (where the exhaust is hottest and makes the catalyser work best) and a muffler can at the back. High-flow cat-back exhaust systems are so-called because the start at the output of the catalyser and replace all the exhaust from there back. They will have larger diameter pipes and a high-flow muffler at the end. Alternatively you can get header-back exhausts which replace everything from the exhaust header to the back, typically removing the catalyser in the process. These are sometimes affectionately referred to as catless or no-kitty exhausts. Adding a sports exhaust system like this can add another 4 to 5hp but you need to make sure you get one which is made by a well respected manufacturer with a good warranty. Because of the change in back-pressure, these exhausts can cause erratic engine problems on some cars that rely on a certain amount of back-pressure to operate properly. Note: back-pressure is the natural resistance to gas-flow in a normal exhaust. The picture here shows an example of a typical factory-fit exhaust on the left versus a high-flow header-back exhaust on the right. KEYING YOUR SPARK PLUGS Picture credit: Pulstar
There's a little known method of squeezing some more efficiency out of your engine, known as spark plug keying. The idea is simple - expose the spark to the incoming fuel- air charge. If the grounding strap on the bottom of the spark plug faces the incoming fuel-air charge, the spark is effectively 'shielded' from the mixture. The image on the left shows a Schlieren photo of a spark emanating from a spark plug tip. You can see the area behind the ground strap doesn't have as much exposure to the spark. Now I know a spark is a spark, and any spark in a fuel-air environment is going to make it burn, but if the spark is facing the intake valves, then there's nothing obstructing the mixture from getting at it. In thousandths of a second, this does actually make a difference to your burn efficiency. The problem is that when you screw a spark plug into your cylinder head, you have no idea which way the electrode gap is pointing. For best efficiency, it needs to be facing the intake valves or ports as I mentioned above. The solution is pretty simple. Before you install the spark plug, use a marker pen to put a mark on the insulator that aligns with the electrode gap at the bottom of the plug. It's important to use a marker pen and not a pencil because pencil lead is graphite, which conducts electricity. You don't want graphite on the outside of your spark plug insulator!
Once the plug is marked, screw it into the cylinder head remembering that you'll need a quarter turn to snug it up. If the mark on the insulator is a quarter turn from facing the intake valves when the spark plug is finger- tight, you'll know once it's snugged down that the gap will be facing the intake valves inside the combustion chamber. If the mark isn't in the right place, don't go over tightening the spark plug to force it into position! You can get keying kits which are basically replacement crush washers that are slightly thicker or thinner than the standard one. They come in one-third, one- quarter and one-half sizes, meaning that they can affect how far you can screw the spark plug in by the matching amount. So if you finger-tighten the spark plug and the mark on the insulator is facing totally the wrong way, once it's snugged down it will still be a quarter turn away from the intake valves. By changing the crush washer to a quarter-turn crush washer, you'll be able to get an extra quarter turn before the spark plug is tight, which will solve your problem and the electrode gap will now be facing the right way.
GAS-FLOWED OR POLISHED CYLINDER HEADS If you've changed your intake system and your exhaust system, there is one other place full of nooks and crannies where intake charges and exhaust gasses can get discombobulated, and that is the internal passageways in the cylinder head (shown in red in the picture here). Most heads are cast from dies, a process where molten metal is poured into a sand or ceramic die to create the required shapes. Small bits of swarf and casting anomalies are normally dealt with where they are visible but it is possible that the airways in the head still have some rough surfaces. Gas-flowing a cylinder head involves taking it off the car and refining those airways with one of two methods. The cheaper and more basic method involves manual polishing using different grades of sanding and polishing tools. These are manually run around the passages, smoothing off rough edges and polishing the airways to a chrome-like finish. The more expensive method involves hooking the cylinder head up to a machine which pumps superheated plasma through the airways, which literally melts a thin layer of them off based on the actual flow of the plasma itself (which mimics airflow). Both methods achieve the same results - teflon-smooth air passages for the intake charge and exhaust gasses. Getting gas-flowed heads can add another 11 to 12hp to the engine, plus if you want to put a large-bore exhaust on the car, then the gas flow method can widen the exhaust ports to match. Rough or smooth? There's an ongoing debate about whether or not polished intakes actually are the best thing for airflow. Some people go with the 'smooth is best' whilst some reckon that a rough intake is better. Chroming or polishing the intakes gives a smooth surface which impedes the airflow less, whilst the rough surface generates turbulent surface 'bubbles' which move slowly, but allow the air on top to skip over them quickly. The point of polished intakes isn't so much to give a smooth surface to the actual intake as it is to make sure there are no kinks, metal seams or casting burrs that will act as a restriction to the airflow. HIGH-LIFT OR LIGHTWEIGHT CAMS
You can squeeze even more power out of your lump if you change the cam or cams at the top of the engine. Lightweight cams weigh less (duh!) and so impose less mechanical drag on the internal parts of the engine. Less weight and less drag mean less power lost to friction and driving the cams themselves. High-lift cams take a slightly different approach. If you look at the 4 stroke diagram way back at the top of the page, you'll see the lobes on the cams are what force the valves to open. The lobes on a normal cam are egg-shaped. On a high-lift cam, they are more rounded-rectangular shapes. The result is that as the lobe spins round, it begins to open the valve sooner, keeps it open longer and then closes it later. The principal is simple : if the valve is open longer, the engine can suck more fuel-air mix in before the combustion cycle. The picture here shows an (exaggerated) example of high-lift cams. The camshaft on the right shows a regular lobe shape and the one on the left shows how a high-lift lobe might look. The difference is subtle but the one on the left would result in the valve opening sooner, staying open longer and closing later. If I'm starting to sound like a scratched record, then you've noticed the overriding theme of getting more power - getting more fuel-air mix into your cylinders by any method possible. As they say on naff informercials But wait - there's more! Let the scratched record continue......
EVEN MORE POWER WATER INJECTION COOLING As weird as this sounds, you can actually make most engines perform better in some circumstances by injecting water directly into the fuel-air mixture. It sounds counterintuitive but the principal is really simple. Vapourising water into the fuel-air mix will cause the air to become denser and cooler. Cool, dense air results in a better charge into the cylinder head, which results in a more powerful burn during combustion. This naturally results in more power. Water injection is used on WRC (World Rally Championship) cars but is detrimental to power when the charge air temperature is below 42°C and boost pressure is below 0.6BAR. Because of this a triggering / shut off system is used on some WRC cars that triggers on at 42°C and shuts back off at 38°C, only triggering when boost is above 0.6BAR. INTERCOOLING Intercooling takes a slightly different poke at the "cooling the fuel-air mix" equation. Intercoolers are normally found on turbo engines and are designed so that atmospheric air flowing around the outside of them cools the air charge from the turbo inside them. The cooler air for the outside can be direct- or indirect-flow. Direct flow designs have the intercooler mounted at the front of the car in the airflow. Indirect-flow units are mounted somewhere in the engine bay with hoses and scoops to get the air to them. WATER-ASSISTED INTERCOOLING An enhancement to standard intercooling is water-assisted intercooling as found on the Subaru WRX STi. Rather than using water injection into the fuel-air charge, it has an intercooler water spray system that sprays water onto theoutside of the intercooler to improve the efficiency of the charge air cooling. The auto version found on the top spec models is ECU-controlled to give 5 second bursts of cooling water when boost is high enough to warrant it. The lower spec versions have a manual switch on the dash that triggers a 5 second burst every time you press the button. CHARGE COOLING Charge coolers are a more sophisticated derivative of water-assisted intercooling. Rather than just spraying water around the outside of the intercooler, they have a water jacket around the core with an external water pump and independent radiator. The pump constantly circulates water through the chargecooler jacket and then out to the radiator, keeping the whole unit cool. Chargecoolers work well until the engine starts being more demanding about power - once they get to a certain point, they're overwhelmed by the amount of air being drawn into the engine. REFRIGERATED INTERCOOLING / CHARGECOOLING Rather than injecting water directly into the air flow, or cooling the body of the chargecooler or intercooler, refrigerated systems force the incoming air over a radiator- like device to cool the air. This heat exchanger is filled with a compressed-gas based and works just like your refrigerator at home. The gas is compressed into a liquid then piped into the heat exchanger. As it turns back into gas, it cools down and hence cools the air flowing over the heat exchanger. The now-gaseous coolant is re-compressed outside the intercooler where it gives off the heat via a secondary radiator positioned in the airflow. Picture credit: Nitrous Oxide Systems NITROUS OXIDE - NOS
Anyone in the street racing scene, or anyone who sawThe Fast and the furious will be familiar with nitrous oxide (N2O), also known by one of the trademarks NoS (Nitrous Oxide Systems - a division of Holley). NoS takes the idea of cooling the inlet charge to extremes. These systems involve an injector unit in the intake system connected via a solenoid release valve to a tank of compressed NoS somewhere else in the car - usually in the boot or trunk. When you push the 'boost' button, the solenoid opens and liquid NoS rushes to the injector. As it vapourises into a gas, it absorbs a phenomenal amount of heat, resulting in a supercooled airflow. At the same time, because it absorbs heat, it splits into oxygen and nitrogen. The normal oxygen content of air is around 20%. With NoS that is pushed up to about 33%. Adding that much oxygen to the intake means you need to also add more fuel otherwise the fuel-air ratio is way off so all NoS kits come with a fuel solenoid and injector too. When you apply the boost, NoS and fuel are forced into a y-nozzle in the airflow just in front of the throttle body. As well as all that plumbing, NoS kits can be enhanced with blow-off valves. If you're sitting at the lights on a drag strip with the NoS system pressurised, it will slowly be evaporating in the system and gaseous NoS is nowhere near as dense as the liquid, compressed form. To get the gaseous stuff out of the line, the blow-off valve is opened by a manual switch in the car to let it out and keep the lines full of liquid NoS. So now you have a highly oxygenated fuel-air mix which is supercooled and thus super dense, being blown into the combustion chamber under pressure, thus forcing more of it in there. The resulting burn is so highly potent that you can easily see a 50hp increase in instantaneous power coming from the engine. Easily. There are however three obvious downsides. The first is that if your boost pressure is too high, you get way too much NoS into the system and the resulting fuel-air mix can burn so violently that it will blow out your head gaskets and/or melt something important inside the engine. You can safely assume about 20hp increase in power per cylinder before you need to start upgrading to racing parts. The second downside is that the very sudden increase in power from the engine can destroy a non-racing clutch, or if you have a racing clutch, it can torque the drive wheels so much that your tyres simply can't grip and more and you start to skid - not good at speed. The third is that the boost is finite. Once your NoS tank is empty, that's it, no more go-go juice. This is why it's typically only used in street or drag racing because the increase in power is very steep, but very short. One last thing: however photogenic the neon purple and green gas was coming from the exhausts in The Fast and the furious, that was just Hollywood eye-candy. Your NoS system will not do that. AN ALTERNATIVE TO MORE POWER : LESS WEIGHT POWER-TO-WEIGHT RATO A lot of people think only about power. They want more and more power but they overlook one thing. The speed and acceleration of your car is directly related to the power-to-weight ratio. This is a measure of how powerful your engine is compared to the weight of the vehicle. So a massive V8 lump in a beefy 60's American muscle car might seem like a good idea, but it might easily be outrun by a highly-tuned 2 litre 4- cylinder engine in a super lightweight Japanese car. The actual units of power-to-weight ratio don't really matter, as long as you use the same units when comparing any two vehicles. So you can't use bhp and weight in kilos to measure one vehicle and hp and weight in pounds for the other. So to illustrate power-to-weight ratio, consider the following example. Subaru do several vehicles in their Impreza lineup. From their 2007 range:
Impreza 2.5i 173hp, 3067 lbs kerb weight Impreza WRX 224hp, 3296 lbs kerb weight Impreza WRX STi 293hp, 3351 lbs kerb weight
(Kerb weight is the total weight of a vehicle with standard equipment, all necessary operating consumables (such as motor oil and coolant), a full tank of fuel). You can see as you go up the range, the weight of the vehicles increases, but so does the horsepower. Power-to-weight ratio is a two-sided equation. A vehicle will go faster with less weight, or more or a combination of the two. With the Subaru example, the power-to-weight ratios look like this:
Impreza 2.5i = 1:17.72 Impreza WRX = 1:14.71 Impreza WRX STi = 1:11.43
The figures are easy to come by - divide the power by the weight to get the ratio. The 'to' in 'power to weight' is like the dividing line in a fraction. So 173hp / 3067lbs = 0.0564334, or in standard notation 1:17.72. You can see that despite the higher-end cars getting heavier, the increase in engine power brings the power-to-weight ratio down so the car becomes quicker. This explains why motorbikes are so quick compared to cars. For example if you compare the 2007 Honda CBR600RR to the 2007 Subaru WRX STi, it becomes readily apparent why the bike will win every time:
Impreza WRX STi = 293hp, 3351 lbs kerb weight = 1:11.43 power-to-weight ratio CBR600RR = 118hp, 345 lbs kerb weight = 1:2.93 power-to-weight ratio
So it's not that the bike is more powerful - it's not. The engine is only 600cc and it produces almost a third the horsepower of the car. But the bike weighs so much less that the weight side of the equation drops to the point where the ratio plummets. WEIGHT IS EVERYTHING So in a car, weight is everything. It can be expensive to start beefing up the engine to give you more power, but it can be really cheap to reduce the weight. As a rough guide, for every 100lbs (45kg) of weight you remove from the average car, you will drop 1/10 second from a timed quarter mile. For the ultimate sports car or street racer, beef up the engine and reduce the weight; increase the power side of the equation and decrease the weight side of the equation and the power-to-weight ratio becomes more favourable. So how do you reduce the weight of your car. Well again it depends on how far you want to go. If you don't care about carrying passengers, toss out the rear and passenger seats. Don't mind getting a flat and calling a tow-truck? Get rid of the spare tyre and jack. If you're going for a true drag-strip car, take out the glass windows and replace them with plastic ones. Remove the dashboard, carpet, headliner, etc.etc.etc. Beginning to get the idea? There's really no limit to how far you can go. One of the most popular weight-saving mods is a carbon fibre hood. If you're interested enough in this topic to have reached this point on the page, then you'll likely have seen cars with carbon hoods - they're very obvious because the hood is almost always black. But why this particular item? Well, the hood of your car provides no structural strength, and it has no crash-absorbing properties in a front-end wreck. It's basically an engine cover. Swapping your factory hood for a carbon fibre one can save something like 4kg (8.8lbs) of weight. Doesn't sound like much? Put 4 bags of sugar in a plastic bag and hold it out at arm's length. That's 4 kilos. People really underestimate the value of weight in a car. It's why race cars are made of sheet aluminium and carbon fibre. It's why they don't have passenger seats. If you're serious about racing your car, shedding weight every bit is as good as adding power. Swap steel wheels for alloys - less unsprung weight and they look better. Swap steel brake discs for carbon-fibre reinforced ceramic ones (standard equipment on some Porsches) and save weight there. Or if you're totally loaded with cash and don't know what to do with it, get pure carbon-carbon discs instead for even more weight saving. Although if you do that, you'll need a healthy disposable income. Carbon-ceramic and carbon-carbon brake rotors do wear annoyingly quickly but you absolutely will stop on a dime.
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A SECOND ALTERNATIVE TO MORE POWER : LESS LOAD ON THE ENGINE In an ideal world, the engine in your car would do one thing - propel you forward. In real life of course it's doing a lot more than that. It's driving the alternator to charge your battery and in most cars now, it's also driving the air conditioning compressor (when active). Both of these items increase the load on the engine. As a rough guide, every 25amps of load on the alternator equals 1hp of load on the engine, whilst running the a/c can typically sap 5% of the engine's power. Automobile blog dyno'd a BMW Z4 with the a/c on and off and registered 232hp / 212lb-ft torque with the a/c off and 221hp / 204lb-ft of torque with the a/c on - quite a drop. So imagine you have a 150hp engine in a vehicle in the summer with the a/c on, running the radio and the seatback DVD player and LCDs for the ankle-biters. You're dropping a couple of horsepower for the electronics in the vehicle (electric power steering, power seats, radio, LT circuit, lights etc) and 7½hp because you're running the air conditioner. Your 150hp engine is now performing like a 140hp engine - you've lost a lot of power there. But what can you do? Well the most obvious thing is turn off the a/c. Unless it's genuinely hot outside, don't use it. For example, in the winter, when you're defrosting the windows on a cold morning - don't turn the a/c on - leave it off. Ok the air won't be so dry but you'll also not be sapping that power from your engine. After that you can look at separate charging and battery circuits for things like the radio or ICE install that only load the engine when they need to charge. Upgrade your alternator to a super lightweight item with professional grade ballbearings on the alternator shaft; this makes the alternator easier to turn and induces less drag on the alternator belt (fractionally). GROUNDING KITS & NOISE ATTENUTATORS / ABSORBERS You could also look at grounding kits although the jury is still out on whether these actually work or not. The idea with a grounding kit is that you beef up the ground straps in your vehicle to ensure an uninterrupted current flow with less resistance. I'm honestly not sure that this would produce a measurable decrease in load on the alternator but you'll find a lot of these kits being flogged on e-bay. The one thing grounding kits are good for are sorting out the electrics on older cars. For some reason the Mazda RX-7 always seems to benefit from revamping the grounding straps. Bear in mind this isn't going to magically increase the performance of your vehicle though - on an older vehicle you're simply making the electrical system closer to how it was when the car was new. The other kit you'll see a lot of are noise attenuators. The claim with these is that they 'clean' the 12v electrical signal of the inherent high-frequency electrical noise, to give the engine management system a better chance to read a clean signal from its various sensors. Most of these systems are simply a large capacitor in a plastic box. A capacitor willremove high frequencies, but the frequencies are dependant on the value of the capacitor and the resistance of the circuit path. Generally speaking, most modern cars already have a suppressor capacitor on the alternator. There's not much harm in adding more, but it would probably be better to fit power filters to each sensor. Without knowing what's inside these devices it would be hard to say if any of them will do what's claimed. Apart from that, if the engine management system is any good it should be able to filter out noisy readings in its software. TURBOS AND SUPERCHARGERS Most people know that a turbo or supercharged engine is more powerful, but do you know why? In simple, sexual innuendo terms, they give more suck before the squeeze, bang and blow of your engine. The basic idea behind both devices is a turbine that sits in the intake airflow. As it spins, it physically sucks more air in than the normal induction of the engine and compresses it further down the line resulting once again in more air in the intake charge, which means better burn which means more power. Both devices are known by the common description of forced induction systems. The difference is the way the two devices are driven. TURBOS
First built in 1925 by Swiss engineer Alfred Buchi, a turbo is normally driven from the exhaust gasses. The faster the exhaust gas passes through one side of the turbo, the faster the exhaust turbine spins and the more air it can force in to the engine using the intake turbine on the other side. This is the source of "turbo lag". When you put your foot down, the engine spools up and produces more exhaust pressure, which spins the turbo and accelerates the incoming air. The lag is the time between putting your foot down and the exhaust gasses getting up enough pressure to make a difference. The advantage of a turbo over a supercharger is that the turbo essentially runs on "waste product". The exhaust leaves the car anyway, so why not make use of it on the way out? A turbo can spin up to 150,000rpm and because it's in the exhaust flow, can reach 800°C in some cases. The picture here shows a cutaway of a typical turbo. The exhaust gasses flow through the brown section at the back, passing over the blades of the centrifugal turbine and turning the shaft connected to the centrifugal intake compressor in the silver section at the front. ANTI-LAG SYSTEMS As I mentioned above, turbo lag is an omnipresent problem. Anti-lag systems help to minimise this by keeping a turbo spinning whilst the throttle is closed - a condition which would normally make the turbo spool down. Anti-lag works by bleeding a little air past the throttle and dumping unburned fuel into the turbine housing to keep it spinning. When the power is required, the initial spool-up is already done and the turbo can provide power more quickly, with reduced lag. ALS can add over 200°C to the temperature of the turbo forcing it up over 1000°C. DUMP VALVES Most turbo cars have dump valves in the intake system. This is a spring-loaded pressure-release valve. Because of turbo lag, you can take your foot off the accelerator intending to slow down, but the turbo can still be spooling up because of the lag. When this happens, the pressure in the intake manifold rises rapidly because the turbo is now trying to jam more air into the engine than it can handle. When the pressure gets to a certain point, the dump valve pops open and relieves the pressure. It's what gives that satisfying "pffssshhhhhhh" sound when you rev a turbo engine with the car standing still.
SUPERCHARGERS Superchargers work slightly differently in that they're normally driven directly from the crank either via a belt or via direct connection to one of the camshafts. With a supercharger, there is little or no lag because you don't have to wait for the exhaust pressure to build up. As soon as the engine starts to spin faster, the supercharger spins faster because of the direct mechanical connection. That advantage is also a disadvantage. Unlike the turbo, a supercharger is imposing a mechanical load on the engine itself, so a percentage of the increase in power is actually taken up simply in driving the supercharger itself. Modern superchargers are quite compact and can sit either on top of, or next to the cylinder head. The most common type, called a twin- screw supercharger, uses a pair of interlocking Archimedes screw compressors (shown on the right) that suck air in and compress it at the same time. Centrifugal superchargers are almost a hybrid between turbos and twin-screw superchargers. They're still driven via a direct mechanical connection, but rather than having the two screws that mesh together, they have a single centrifugal compressor that looks like the intake turbine in a turbo (above). "Classic" superchargers are what you see poking out of the hoods of souped-up 70s Americana with huge air scoops and giant belt-driven compressors. The picture to the left shows a top-mounted belt-driven supercharger. EXHAUST WRAP This little section almost needs to be considered along with turbos, above, because the two typically go hand-in-hand. When gas gets hot, it gets less dense. Less dense means less resistance to flow. It figures, then, that people who are looking at every tiny minutae of performance would want to wrap their exhaust headers. Why? Well exhaust gas exits the combustion chamber extremely hot (duh!) but it cools rapidly as it travels through the exhaust system. In doing so, two things happen. First, the gas becomes more dense and begins to resist flow, and second, as it does this, it disperses heat into the metal exhaust pipes, which in turn radiate the heat into the engine bay, raising the under-hood temperatures. The problem with the gas cooling down is obvious - it begins to slow down and provide resistance in the exhaust system. The problem with the under-hood temperatures going up is that it makes it more difficult for the engine to get a good, cold charge of air. (Colder air is more dense, which means better, more powerful combustion.) This is why you sometimes see vented hoods on cars; they're designed to let the hot air out and keep the under-hood temperatures down. So wrapping the exhaust headers with exhaust wrap helps because it basically insulates the metal exhaust pipes. This means they retain the heat better which in turn means the exhaust gas remains less dense and keeps up it's high flow rate. For turbos, this is a good thing because it means the exhaust reaching the turbo is travelling faster, which means the turbo spins faster, which means more air forced into the engine. Everything is connected, you see? So the ideal system would be a turbo, with wrapped exhaust headers, a vented hood, a cold-air unduction and an intercooler. That combination, whilst expensive, will give the coldest (and thus densest) fuel-air charge into the engine, whilst insulating the exhaust and ventilating the engine bay at the same time. It's worth pointing out that not all exhaust wraps are made equal. If the wrap insulates too well, then the exhaust pipes get too hot and that can cause all it's own problems from engine bay fires to structural failure of the exhaust or turbo. Point to note: It's only a rumour that exhaust wrap absorbs water and can encourage your mild steel headers to crumble away prematurely. If anyone tells you this, they're fearmongering. FUEL ADDITIVES AND RETROFIT "EFFICIENCY" DEVICES "A fool and his money are easily parted". No saying holds more truth than in the motoring world. There are tens, perhaps hundreds of companies out there all claiming to manufacture devices which give better fuel economy, cut down on emissions, add to engine longevity etc. For the most part, these products are elaborate cons. And in some cases, not-so-elaborate. For as long as people are gullible, and can be led by advertising hype, these companies will thrive. What you need to consider is one very important question : If these devices work, why do the manufacturers not put them on their cars as standard? Surely selling a Subaru equipped with a device that gives 8% better economy than the equivalent Nissan would be a killer sales pitch?. Well the answer is blindingly simple: these devices don't work as advertised. There's an important distinction there because a lot these devices do something but just not necessarily to the level promoted in the advertising. Often nowhere near that level.
For the lawyers out there, I'm not attempting to be defamatory about these products. I'm attempting to educate. If your company can prove to me that these devices work, I'll happily change my articles. Contact me for where to send free samples to for testing. Without further ado, then..... MPG CAPS, FFI AND ALL THE OTHER "PILL IN YOUR FUEL TANK" MIRACLE WORKERS Status : Tested Websites : myffi.biz and mileagesecrets.com MPG Caps, or any of the other "pill in your fuel tank" products are the cheapest and easiest-to-find miracle cures for increased power and gas mileage. The products are simple. They're normally pills, in a pop-out wrapper just like medical pills, or in a bottle. They smell foul and the manufacturers claim that one pill per 20 gallons of fuel will give you increased power and performance whilst at the same time cutting your mpg (in some cases they claim up to 30%). Explanations range from "organic engine conditioner that improves fuel economy and power by creating a micro-thin coating on the combustion chamber allowing fuel to burn better"all the way up to the fantastical "nanotechnology particles that seek out and change the molecular structure of refined gasoline to make it burn more efficiently". Wow. Impressive stuff. Typically these pills are biodegradable plant or sugar compounds laced with food colouring and some odd petrochemical to give them an official smell. They don't work. ABC reported on a AAA test of the MPG Caps and found their claims to be invalid.ABC report. Texas recently closed down Bioperformance Inc. for fraud linked to their magic fuel pill: Report. For my test of the MPG Caps fuel pills head over to my Product Reviews page.
THE MPT SMOGBUSTER™ Status : Untested Websites : fueldisc.com and/or fuel-disk.net If I started this paragraph by telling you that a device projected "holographic frequencies into the gas tank and changes the molecular structure of the gasoline" what would you think? Well it seems that plenty of people think enough of that statement to cough up $299 for a plastic disc with some fancy silk-screen printing on it. The idea is, apparently, that the molecularly-changed fuel burns more efficiently thus giving you better gas mileage and less emissions. It's about the size of a US quarter or a UK 10p piece and is supposed to - wait for it - be taped to the underside of your gas tank. The website even helpfully suggests that superglue could be used. From the Denverpost.com : "It doesn't work," says Dr. Terry Parker, a physics professor at the Colorado School of Mines. Parker and graduate student John Dane of the chemistry department tested the device for 9News. "It's clear that it's just a sticker and nothing else," Dane said. What should set alarm bells ringing with this device is that it's sold through multi-level marketing, the new buzzword for pyramid selling. The more of these units you sell, the cheaper they get for you to buy. The best part of the sales pitch is this section : OceanCity Network, Inc. is proud to offer a 30 day 100% money back guarantee if not completely satisfied. To qualify for a full refund, the MPT SmogBuster™ must remain adhered to the paper in which it was shipped on.. So if you unstick it and use it, you can't get your money back. However, they add that to test it, you can simply duct-tape the thing to the gas tank, complete with it's backing paper. So even if the device was electrical (which the silk-screen printing might lead you to believe), putting a piece of paper in the way would prevent it from making any contact with the metal of your tank. I also suspect that trying to remove the duct tape from the fuel disc without removing the fuel disc from the backing paper is going to be next to impossible. One last point to note : most fuel tanks are covered in a rubberised underseal protection - there's no metal to stick this thing to in the first place..... THE TORNADO FUEL SAVER
Status : Tested Websites : tornadofuelsaver.com This thing is known by many, many different names, including the Cyclone-Z Fuel Saver and the Dynamix Fuel Saver. The basic premise is to make you believe that by swirling the air in your intake manifold, you'll get a better fuel-mix which will result in cleaner burning, longer-lasting, more emission-friendly engines, that at the same time give more horsepower. It's a great theory, and for $69, who could resist? The theory is sound. So sound in fact that carburetors and fuel systems have been swirling the air in the intakes for decades. It's called the venturi effect and it's why carburetors can freeze up in the winter. John Matarese of the "Don't Waste Your Money" website has a good writeup of a Tornado review. You can find it atthis link. His results? Less than a 1% increase in fuel economy. Not quite the 20-30% promised. The US E.P.A has not tested the tornado fuel saver, but after testing more than 100 similar products including the Cyclone-Z (report PDF) and the Dynamix (report PDF), the E.P.A says it "has not found any product that significantly improves gas mileage." Let's face it. If these things really worked, GM, Ford, Volvo, BMW and all other manufacturers would be buying them by the millions, and cars would come out of the factory with them on. And speaking of the factory, bear in mind that most car manufactures can and will use an engine add-on as a reason not to honour your warranty. For my test of the Tornado, head over to my Product Reviews page. MAGNETIC FUEL TREATMENTS Status : Tested Websites : too many to list. If you drive a car, you're absolutely guaranteed to have heard this claim before : "put a magnet on the fuel line and it will increase your fuel economy by making the fuel burn more efficiently." There's many reasons that these devices typically don't work. Here's just a few of them: . The magnets are tiny, and pretty weak. A magnet cannot provide oxygen and neither can it change the amount of heat released from burning the fuel. It can effect the fuel through diamagnetic influence but that's never been proven to have any measurable effect on gas mileage. . Liquids cannot "retain" any magnetic effect when they leave the magnet, even if affected when within it. Hence you cannot "charge up" a liquid in the way that a dust particle can be charged. . There is no truly independent lab analysis which could give evidence that combustion can be improved nor that you'll get better power output or lower emissions. THE ELECTRONIC ENGINE IONIZER Status : Untested Websites : Engineionizer.com This is an interesting device that takes a different, but similar doublespeak approach to making you believe you can get better fuel economy. Their device consists of a jumble of wires connected to plastic blocks which clamp around your spark plug cables. This is directly from their description:
When a spark plug fires, the capacitor block attached to each spark plug wire picks up a high voltage, low amperage charge (sometimes called a "Corona Charge"). This charge is transferred from the firing cylinder to the other non-firing cylinders via the harness wire. These charges cause a partial breakdown in the larger hydrocarbon molecules in all the non-firing cylinders, resulting in increased combustion efficiency. This translates into better fuel mileage (economy), more horsepower, easier starting, less pollution (lowered emissions), smoother idle.
Let me decode that for you : they claim to fire the spark plugs in the cylinders that don't need firing. The spark is supposed to cause a breakdown in the gas left in the cylinder which somehow makes the next fuel/air charge burn more efficiently.
First of all there's the deviously misused definition of "corona charge". That's actually a wire which emits a static electric charge in a halo around itself. It's normally used in reference to laser printers (!) If spark plug wires did this, you wouldn't be able to hold them whilst the engine was running, nor would you be able to have them touch or be near anything metal in the engine bay. If they were constantly generating static electric charge, you'd also not be able to listen to your radio either. So seeing that caused me to want to work through the rest of the description one step at a time. . A capacitor block picks up a charge from the spark plug cable. Hmm. Well a capacitor stores charge - it doesn't pick it up. For a capacitor to get any charge at all, it would need to be physically wired in to the spark plug circuit. So instead you'd need an inductive loop. Inductive loops generate current because of Faraday's law - it's all to do with magnetism. The brief pulse of current through the spark plug cable generates a magnetic field. The coil of wire sitting inside the magnetic field induces current in its own circuit. . The charge is transferred to the non-firing cylinders via the harness wire. Actually it isn't. The induced current is transferred along the harness wires to the other inductive loops. The result is a brief inducance back into the other spark plug wires, but at a reduced amount due to resistance in the wiring. The current induced in the other spark plug cables would be nowhere near enough to fire the spark plugs. But lets' give them the benefit of the doubt again and assume the other plugs to spark...... These charges cause a partial breakdown in the larger hydrocarbon molecules in all the non-firing cylinders. (sigh). Ok - the charge isn't doing anything to the cylinders at all. The spark plug might be sparking, but even if it is, given the basic design of a 4 stroke engine, there is nothing to burn in the cylinders unless the fuel-air mix is in there. In fact, trying to initiate a spark too early could result in detonation, which would actually damage your engine. Honestly if this idea had any merit, it would be a lot simpler to just wire all the spark plug cables together so they all fired every time one of the cylinders reached it's firing position. Think of how much simpler engine timing would be! Sadly for EngineIonizer, there's a reason why engine manufacturers only fire one spark plug at once. Although having said that, one reader did contact me with the following snippit of information: On the subject of The Electronic Engine Ionizer, you say "there's a reason why engine manufacturers only fire one spark plug at once". As a small note, some manufacturers have simplified ignition systems (Yamaha's YZF-OW01 and YZF-R1 come to mind) which fire cylinders in pairs - one near TDC of the compression stroke and one near TDC of the exhaust stroke. When I did a little work with Kingston Kawasaki (a BSB privateer team) we switched over to this system: there was no power gain, about 1.5 kg weight saving and the spark plug life dropped by about a quarter. I've only ever seen this in 4-cyl engines, although I think some early British twins did this too. That in turn resulted in another email from another reader: I used to own a 1979 Yamaha XS650 (twin cylinder Triumph ripoff, if you don't know them) with electronic ignition. It had a 360 degree crank, so Yamaha figured there was no harm in having the sparks go off each rotation so that's what they did - every time the cylinder went past TDC there was a spark, whether it was a compression or exhaust stroke. Cheap to manufacture but it had no effect on fuel consumption or power. THE ECOTEK CB-26P
Status : Untested Ecotek PLC are marketing a device in England which clamps on to your intake manifold. According to the doublespeak on their site, this device improves performance by collapsing the manifold vacuum so that when the throttle is reapplied, there'll be slightly more fuel in the air-fuel mix and that will improve the throttle response. The hype also claims that the device creates greater turbulence and swirl, which promote better suspension of fuel molecules. And finally, the all-encompassing claims of better fuel economy, better acceleration and more power are all present and correct. One slight problem. This device claims to work during overrun - when you take your foot of the accelerator and the car uses engine-braking. In those conditions, 100% of modern fuel-injected cars cut off the fuel supply. And on older carburettor engines, there's no proof this device does anything at all. In fact there's so little proof that this product has been complained about enough in England to reach the advertising standards authority. You can read their report on it here. In short : waste of money. Once again ask yourself the same question : (all together now) "If it's so good, why don't manufacturers fit it to their cars as standard?" THE "+20BHP CHIP" CONVERSION Status : Untested This is a great scam doing the rounds of ebay in Europe. Search for "mod + 20 bhp" and you'll see literally hundreds of these things going very cheaply. (Better still click here to pop up a new browser window with the search in it). If you are suckered into buying one of these, you'll get a kit containing a resistor that you connect to the positive line of your air intake temperature sensor. The idea is that it fools the ECU into thinking the air charge is colder than it actually is. So why does they claim this works? The claim is that the ECU will be fooled into increasing the fuel in the fuel-air mixture making the engine rev better, and adding 20bhp to the power. Of course like all these scams, that's not quite the case. First of all, it's the air which would make the engine run better, not the fuel. That's why turbos and superchargers push more air into the cylinders. By running more fuel, you basically run a richer engine which makes the engine run cooler. As well as that, all EFI engines have lambda sensors to measure the actual fuel-air ratio and the ECU takes this reading and adjusts the fueling accordingly. It doesn't simply do it from the intake air temperature. So if you fit one of these devices, this is what happens: 1. The ECU gets a reading from the IAT, and adds more fuel. 2. The Ecu then gets the actual fuel-air ratio info from the lambda sensor, realises it's over fueling and cuts the amount of fuel it puts in. 3. The cycle repeats until the excess fuel totally destroys your expensive catalytic convertor. 4. The ecu will also adjust the igniton timing everytime it gets new info. This means the ignition map is constantly changing which could eventually cause the engine to knock/pink, but will certainly make it run rougher than a tractor.
As with most of these scams, there's a Q&A associated with them designed to make you believe the device will work. In this case, it looks something like this. I've debunked each Q&A on a per-item basis. What is this Device? It is a resistor chip that gives out a constant reading of air temperature to your ECU. Sorry, it isn't. It's a 40¢ resistor that lowers the voltage coming from the sensor. A chip is made of silicon and has many layers of circuitry laid out in it, and it requires a special plug - similar to the chip inside your PC or the ECU in the car.
Will my car accelerate faster with this electronic device? Yes! This is the whole point! It has been dyno proven that this device will add up to 20 HP to your vehicle! Really? Because the dyno graphs on e-bay are so obviously faked that I'd believe an untrained 3-year-old could do a better job. I'd like to see actual proof of this from a reputable dyno shop.
Will this device damage my car? Absolutely not. Since the altered signal will always stay within the manufacturer's specifications, there is no way for your engine to get damaged in any way. Yeah - not technically true. You are fooling the engine into thinking it has a cooler air charge, therefore the fueling will be altered beyond the manufacturers specification for the given air temperature, and that could damage your engine.
Like I've said above in this page - if this really worked, why wouldn't the car manufacturers simply re-map their ECUs to perform like this? Or add this resistor to their circuits themselves? Simple - because it does not work. VOLTAGE STABILISERS AND GROUNDING KITS
Status : Untested, but I've been in contact with the manufacturer I've seen a few websites kicking around that advertised massive benefits in fitting their voltage stabilisers and grounding kits to vehicles. Votech Performance is one such company. Their doublespeak (in very poor English by the way) is technically correct. If you connect a car alternator directly to the battery and run all the electrical circuits off it, then you're going to be subject to high-frequency noise in the power supply as well as fluctuations in voltage due to engine loading. They're also correct in asserting that a voltage stabiliser kit and some decent grounding connections will help minimise these issues. What they fail to mention on their website is that almost every new car on the market today (and probably since the mid 90's) has a voltage stabiliser in it. Basically it's a collection of passive components (ie. that draw no power) like capacitors, arranged such that any voltage spikes can be capped off, and the high frequency noise can be reduced. For the grounding wires, check under the hood of your car. Those gigantic copper braided cables connecting the battery and engine to the body of the car and the fusebox are your grounding cables. Pretty significant sized cables too. The reason for these bits is the ECU - vehicle manufacturers don't want random power fluctuations reaching the sensitive electronic components in the engine management system. By default, the inclusion of any sort of chip-based engine management means the manufacturer must include voltage stabilisation in their electrical system. So - outfits like Votech are entirely correct in their assertions, but miss out the important fact that your car already has the stuff they're selling. However in July 2006, Votech contacted me directly to address some of my comments here. What wasn't clear from their website, but has been made clear since, is that Votech's target market is for local Malaysian-built cars, Korean cars (except for Kia and the Hyundai Sonata which has voltage noise suppression from the factory) and Japanese cars for the Asian market. It seems the standards of manufacture with their vehicles are so poor that the electrical systems are all over the place, and there's a lot of difference between Japanese cars for the west versus those for the Asian markets. What Votech are selling is basically what the Malaysian manufacturers don't put in their vehicles as standard but what we in the "west" take for granted. Their marketing guru told me "We advise our customers before we sell to them. Customers who driving BMW, Merc, Audi, Fiat, VW and other continental cars are advised that our product isn't necessary. If a customer insists they want it, then we will proceed with the installation." OK so now with that in mind, when we look at the claims, whilst they read pretty poorly to anyone with an American, Japanese or European car, I can imagine for Votech's target market they might actually make sense. Votech tell me that they can provide anyone who asks with independent lab results gained from dyno testing. . Increased Torque - how? Votech claim that the better voltage response in the low tension circuit results in better response in the high tension circuit. This could result in a more powerful spark which might give a better burn in the combustion chamber. It's possible on Malaysian-built cars then that this would result in more torque. . Better throttle response - this is all to do with how the engine sensors read their data and send it back to the ECU. If they're getting crappy, noisy voltage, then the readings being sent back to the ECU could be all over the place, meaning it could have trouble generating good throttle position information from the engine map. If the sensors are allowed to do their work properly, the ECU might be able to do a better job of mapping it all out, and the result could be better throttle response. . Brighter headlights - this could be true except their product would need to be generating either more than 12v or higher current. Well again you need to look at it from the perspective of their target market. If their cars have headlights that get brighter the more you rev the engine, then Votech's product could stabilise the voltage and give a more consistent light output. . Improved audio quality - now this one I could go with, especially if you listen to AM radio. But again, most modern Euro, Japanese and American cars have stabilisation and noise-suppression built into the factory 12v system. . Improved Fuel Efficiency. Fuel efficiency would seem to have nothing to do with the 12v electrical system. But technically, the alternator is in the 12v electrical system, and load on the alternator can affect fuel efficiency by adding mechanical drag to the engine. The more load on the electrical system, the more drag in the alternator. The difference between a shoddy 12v system and a decent one can be up to 3% in fuel efficiency. . Colder air-con - this is a bit of a wild claim. The a/c compressor is belt-driven off the engine crank. The only electrical component is the fan that blows the air into the car, and that doesn't make the air colder, it just moves it around. However Votech reported to me that they did get a 2°C drop in temperature coming out of the vents on their Alfa test vehicles. Quite why this would be, I don't know. FURTHER INSIGHT I was contacted in 2011 by Ricky Willems, a senior electrical engineering and product design major at Rensselaer Polytechnic Institute, a member of SAE and IEEE. (His extracurricular work includes designing hybrid electric race cars and vehicle ECUs). He had some insight into voltage stabilisers:
I own a Pontiac Montana van that has gone through 3 separate stock voltage stabilizers. The electrics were poorly implemented, and water has repetitively damaged the electronic controls. In addition, I have been in situations where the jiggling of grounding wires brings the voltage back into regulation temporarily. Because of these failures, Ive had opportunity to judge the effects of having or not having a voltage stabilizer on a modern EFI car that was designed to operate with one. I imagine this would be a similar situation to asian market cars that did not include one, despite having an otherwise similar design to western models.
The only claim I cannot support that you list is the colder AC, which I have not noticed, but then again likely wouldn't as I don't use AC very often anyway.
I can support increased torque, Better throttle response, and Improved Fuel Efficiency. The voltage variations send rippling voltages to the cars sensors, which then report back flawed data to the internally regulated ECU. The engine can normally adjust for errors, but since the errors are transient and continuous, the ECU cannot adapt. As such, according to my OBDII connection, the values reported vary from what they should and impact fuel mixture negatively, causing a loss in torque, loss in fuel economy, and strange (though not "slow") throttle response.
Audio quality on my vehicle has not been impacted, as it is also internally regulated, but I have had stereos on vehicles with no regulation that suffer severely for it. Many vehicles, even with a solid voltage stabilizer system still have too much noise for after- market stereo systems to sound clear and interference free.
As for brighter headlights, the claims are half true. When my regulation is off, the headlights flicker severely with the pulsing of the alternator. The appear dim, although each flash is actually brighter than the headlights would regularly be. The flashing makes it appear otherwise though. (your eyes adjust to the brighter light output, only to have it taken away 50% of the time)
My only -guess- on the air conditioning is that it may make it cooler at idle, when the more properly running engine would smooth out its idle, and have a more consistant AC output. Mind you its only a guess. RESOURCES FOR THE CURIOUS There is an excellent site which covers all the above and a lot more with engineering and scientific analysis of all these products. If you really think they work, then drop in at fuelsaving.info and find out how clever the marketing hype is, and how little any of these devices actually work.
The FTC have a page dedicated to warning the public about these scams. Click here for the FTC's "Gas-Saving" Products: Fact or Fuelishness? page.
The Environmental Protection Agency (E.P.A) has evaluated or tested more than 100 of these alleged gas-saving devices and has not found any product that significantly improves gas mileage. In fact, some "gas-saving" products may damage a car's engine or cause substantial increases in exhaust emissions. Click over to epa.gov and put "gas saving" in their search box.
One of the best sources of information on the E.P.A site is their page on Gas Saving and Emission Reduction Devices Evaluation.. Here you can find downloadable PDF reports on everything from the FuelXpander to the sexually deviant-named Analube Synthetic Lubricant.
EPA Evaluation of Aftermarket Gas - Saving Products (PDF) EPA Motor Vehicle Aftermarket Retrofit Device Evaluation Program (PDF) Environmental Fact Sheet: Aftermarket Gas Saving Products and EPA Product Evaluations (PDF) TELL ME MORE If you've got a device you've bought and tested, or you'd like to know more, drop me a line. The more of you that contact me, the more complete this page will become. THE STEERING BIBLE STEERING : ESSENTIAL TO DRIVING Elsewhere on this site you can learn about all the other stuff that makes a car go and stop, so this page is where you'll learn about how it goes around corners. More specifically, how the various steering mechanisms work. Like most things in a car, the concept of steering is simple - you turn the steering wheel, the front wheels turn accordingly, and the car changes direction. How that happens though is not quite so simple. Well - it used to be back in the days when cars were called horseless carriages, but nowadays, not so much. BASIC STEERING COMPONENTS
99% of the world's car steering systems are made up of the same three or four components. The steering wheel, which connects to the steering system, which connects to the track rod, which connects to the tie rods, which connect to the steering arms. The steering system can be one of several designs, which we'll go into further down the page, but all the designs essentially move the track rod left-to-right across the car. The tie rods connect to the ends of the track rod with ball and socket joints, and then to the ends of the steering arms, also with ball and socket joints. The purpose of the tie rods is to allow suspension movement as well as an element of adjustability in the steering geometry. The tie rod lengths can normally be changed to achieve these different geometries.
THE ACKERMANN ANGLE (OR WHY YOUR WHEELS DON'T POINT THE SAME DIRECTION) In the simplest form of steering, both the front wheels always point in the same direction. You turn the wheel, they both point the same way and around the corner you go. Except that by doing this, you end up with tyres scrubbing, loss of grip and a vehicle that 'crabs' around the corner. So why is this? Well, it's the same thing you need to take into consideration when looking at transmissions. When a car goes around a corner, the outside wheels travel further than the inside wheels. In the case of a transmission, it's why you need a differential (see the Transmission Bible), but in the case of steering, it's why you need the front wheels to actually point in different directions. On the left is the diagram from the Transmission Bible. You can see the inside wheels travel around a circle with a smaller radius (r2) than the outside wheels (r1).
In order for that to happen without causing undue stress to the front wheels and tyres, they must point at slightly different angles to the centreline of the car. The diagram to the left shows the same thing only zoomed in to show the relative angles of the tyres to the car. It's all to do with the geometry of circles. This difference of angle is achieved with a relatively simple arrangement of steering components to create a trapezoid geometry (a parallelogram with one of the parallel sides shorter than the other). Once this is achieved, the wheels point at different angles as the steering geometry is moved. Most vehicles now don't use 'pure' Ackermann steering geometry because it doesn't take some of the dynamic and compliant effects of steering and suspension into account, but some derivative of this is used in almost all steering systems (right). WHY 'ACKERMANN'? This particular technology was first introduced in 1758 by Erasmus Darwin, father of Charles Darwin, in a paper entitled "Erasmus Darwin's improved design for steering carriages--and cars". It was never patented though until 1817 when Rudolph Ackermann patented it in London, and that's the name that stuck. STEERING RATIOS Every vehicle has a steering ratio inherent in the design. If it didn't you'd never be able to turn the wheels. Steering ratio gives mechanical advantage to the driver, allowing you to turn the tyres with the weight of the whole car sitting on them, but more importantly, it means you don't have to turn the steering wheel a ridiculous number of times to get the wheels to move. Steering ratio is the ratio of the number of degrees turned at the steering wheel vs. the number of degrees the front wheels are deflected. So for example, if you turn the steering wheel 20° and the front wheels only turn 1°, that gives a steering ratio of 20:1. For most modern cars, the steering ratio is between 12:1 and 20:1. This, coupled with the maximum angle of deflection of the wheels gives the lock- to-lock turns for the steering wheel. For example, if a car has a steering ratio of 18:1 and the front wheels have a maximum deflection of 25°, then at 25°, the steering wheel has turned 25°x18, which is 450°. That's only to one side, so the entire steering goes from -25° to plus 25° giving a lock-to-lock angle at the steering wheel of 900°, or 2.5 turns (900° / 360). This works the other way around too of course. If you know the lock-to-lock turns and the steering ratio, you can figure out the wheel deflection. For example if a car is advertised as having a 16:1 steering ratio and 3 turns lock-to-lock, then the steering wheel can turn 1.5x360° (540°) each way. At a ratio of 16:1 that means the front wheels deflect by 33.75° each way. For racing cars, the steering ratio is normally much smaller than for passenger cars - ie. closer to 1:1 - as the racing drivers need to get fuller deflection into the steering as quickly as possible. TURNING CIRCLES The turning circle of a car is the diameter of the circle described by the outside wheels when turning on full lock. There is no hard and fast forumla to calculate the turning circle but you can get close by using this: turning circle radius = (track/2) + (wheelbase/sin(average steer angle))
The numbers required to calculate the turning circle explain why a classic black London taxi has a tiny 8m turning circle to allow it to do U-turns in the narrow London streets. In this case, the wheelbase and track aren't radically different to any other car, but the average steering angle is huge. For comparison, a typical passenger car turning circle is normally between 11m and 13m with SUV turning circles going out as much as 15m to 17m.
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STEERING SYSTEM DESIGNS : PITMAN ARM TYPES There really are only two basic categories of steering system today; those that have pitman arms with a steering 'box' and those that don't. Older cars and some current trucks use pitman arms, so for the sake of completeness, I've documented some common types. Newer cars and unibody light-duty trucks typically all use some derivative of rack and pinion steering.
Pitman arm mechanisms have a steering 'box' where the shaft from the steering wheel comes in and a lever arm comes out - the pitman arm. This pitman arm is linked to the track rod or centre link, which is supported by idler arms. The tie rods connect to the track rod. There are a large number of variations of the actual mechanical linkage from direct-link where the pitman arm is connected directly to the track rod, to compound linkages where it is connected to one end of the steering system or the track rod via other rods. The example here shows a compound link (left). Most of the steering box mechanisms that drive the pitman arm have a 'dead spot' in the centre of the steering where you can turn the steering wheel a slight amount before the front wheels start to turn. This slack can normally be adjusted with a screw mechanism but it can't ever be eliminated. The traditional advantage of these systems is that they give bigger mechanical advantage and thus work well on heavier vehicles. With the advent of power steering, that has become a moot point and the steering system design is now more to do with mechanical design, price and weight. The following are the four basic types of steering box used in pitman arm systems. WORM AND SECTOR
In this type of steering box, the end of the shaft from the steering wheel has a worm gear attached to it. It meshes directly with a sector gear (so called because it's a section of a full gear wheel). When the steering wheel is turned, the shaft turns the worm gear, and the sector gear pivots around its axis as its teeth are moved along the worm gear. The sector gear is mounted on the cross shaft which passes through the steering box and out the bottom where it is splined, and the the pitman arm is attached to the splines. When the sector gear turns, it turns the cross shaft, which turns the pitman arm, giving the output motion that is fed into the mechanical linkage on the track rod. The following diagram shows the active components that are present inside the worm and sector steering box. The box itself is sealed and filled with grease.
WORM AND ROLLER The worm and roller steering box is similar in design to the worm and sector box. The difference here is that instead of having a sector gear that meshes with the worm gear, there is a roller instead. The roller is mounted on a roller bearing shaft and is held captive on the end of the cross shaft. As the worm gear turns, the roller is forced to move along it but because it is held captive on the cross shaft, it twists the cross shaft. Typically in these designs, the worm gear is actually an hourglass shape so that it is wider at the ends. Without the hourglass shape, the roller might disengage from it at the extents of its travel.
WORM AND NUT OR RECIRCULATING BALL
This is by far the most common type of steering box for pitman arm systems. In a recirculating ball steering box, the worm drive has many more turns on it with a finer pitch. A box or nut is clamped over the worm drive that contains dozens of ball bearings. These loop around the worm drive and then out into a recirculating channel within the nut where they are fed back into the worm drive again. Hence recirculating. As the steering wheel is turned, the worm drive turns and forces the ball bearings to press against the channel inside the nut. This forces the nut to move along the worm drive. The nut itself has a couple of gear teeth cast into the outside of it and these mesh with the teeth on a sector gear which is attached to the cross shaft just like in the worm and sector mechanism. This system has much less free play or slack in it than the other designs, hence why it's used the most. The example below shows a recirculating ball mechanism with the nut shown in cutaway so you can see the ball bearings and the recirculation channel.
CAM AND LEVER
Cam and lever steering boxes are very similar to worm and sector steering boxes. The worm drive is known as a cam and has a much shallower pitch and the sector gear is replaced with two studs that sit in the cam channels. As the worm gear is turned, the studs slide along the cam channels which forces the cross shaft to rotate, turning the pitman arm. One of the design features of this style is that it turns the cross shaft 90° to the normal so it exits through the side of the steering box instead of the bottom. This can result in a very compact design when necessary.
STEERING SYSTEM DESIGNS : RACK AND PINION
This is by far the most common type of steering you'll find in any car today due to it's relative simplicity and low cost. Rack and pinion systems give a much better feel for the driver, and there isn't the slop or slack associated with steering box pitman arm type systems. The downside is that unlike those systems, rack and pinion designs have no adjustability in them, so once they wear beyond a certain mechanical tolerance, they need replacing completely. This is rare though. In a rack and pinion system, the track rod is replaced with the steering rack which is a long, toothed bar with the tie rods attached to each end. On the end of the steering shaft there is a simple pinion gear that meshes with the rack. When you turn the steering wheel, the pinion gear turns, and moves the rack from left to right. Changing the size of the pinion gear alters the steering ratio. It really is that simple. The diagrams here show an example rack and pinion system (left) as well as a close-up cutaway of the steering rack itself (right). VARIABLE-RATIO RACK AND PINION STEERING This is a simple variation on the above design. All the components are the same, and it all works the same except that the spacing of the teeth on the rack varies depending on how close to the centre of the rack they are. In the middle, the teeth are spaced close together to give slight steering for the first part of the turn - good for not oversteering at speed. As the teeth get further away from the centre, they increase in spacing slightly so that the wheels turn more for the same turn of the steering wheel towards full lock. Simple. VEHICLE DYNAMICS AND STEERING - HOW IT CAN ALL GO VERY WRONG Generally speaking, when you turn the steering wheel in your car, you typically expect it to go where you're pointing it. At slow speed, this will almost always be the case but once you get some momentum behind you, you are at the mercy of the chassis and suspension designers. In racing, the aerodynamic wings, air splitters and undertrays help to maintain an even balance of the vehicle in corners along with the position of the weight in the vehicle and the supension setup. The two most common problems you'll run into are understeer and oversteer. UNDERSTEER Understeer is so called because the car steers less than you want it to. Understeer can be brought on by all manner of chassis, suspension and speed issues but essentially it means that the car is losing grip on the front wheels. Typically it happens as you brake and the weight is transferred to the front of the car. At this point the mechanical grip of the front tyres can simply be overpowered and they start to lose grip (for example on a wet or greasy road surface). The end result is that the car will start to take the corner very wide. In racing, that normally involves going off the outside of the corner into a catch area or on to the grass. In normal you-and-me driving, it means crashing at the outside of the corner. Getting out of understeer can involve letting off the throttle in front- wheel-drive vehicles (to try to give the tyres chance to grip) or getting on the throttle in rear-wheel-drive vehicles (to try to bring the back end around). It's a complex topic more suited to racing driving forums but suffice to say that if you're trying to get out of understeer and you cock it up, you get.....
OVERSTEER
The bright ones amongst you will probably already have guessed that oversteer is the opposite of understeer. With oversteer, the car goes where it's pointed far too efficiently and you end up diving into the corner much more quickly than you had expected. Oversteer is brought on by the car losing grip on the rear wheels as the weight is transferred off them under braking, resulting in the rear kicking out in the corner. Without counter-steering (see below) the end result in racing is that the car will spin and end up going off the inside of the corner backwards. In normal you-and-me driving, it means spinning the car and ending up pointing back the way you came.
COUNTER-STEERING
Counter-steering is what you need to do when you start to experience oversteer. If you get into a situation where the back end of the car loses grip and starts to swing out, steering opposite to the direction of the corner can often 'catch' the oversteer by directing the nose of the car out of the corner. In drift racing and demonstration driving, it's how the drivers are able to smoke the rear tyres and power-slide around a corner. They will use a combination of throttle, weight transfer and handbrake to induce oversteer into a corner, then flick the steering the opposite dirction, honk on the accelerator and try to hold a slide all the way around the corner. It's also a widely-used technique in rally racing. Tiff Needell - a racing driver who also works on some UK motoring programs - is an absolute master at counter-steer power sliding. THE WHEEL & TYRE BIBLE Are you confused by your car tyres, or if you're American, your tires? Don't know your rolling radius from your radial? Then take a good long look through this page where I hope to be able to shift some of the mystery from it all for you. At the very least, you'll be able to sound like you know what you're talking about the next time you go to get some new tyres. HOW TO READ YOUR TYRE MARKINGS This is probably the number one question I get asked - "how do I read my tyre markings?". It's confusing isn't it? All numbers, letters, symbols, mysterious codes. Actually, most of that information in a tyre marking is surplus to what you need to know. So here's the important stuff: How to read your tire markings
Ke y Tyre Marking Description A Manufacturers or brand name, and commercial name or identity. Tyre size, construction and speed rating designations. Tubeless designates a tyre which requires no inner tube. See tyre sizes and speed ratings below. DIN-type tyre marking also has the load index encoded in it. These go from a load index of 50 B (190kg) up to an index of 169 (5800kg). C Denotes type of car tyre construction. M&S denotes a car tyre designed for mud and snow. Reinforced marking only where D applicable. E Pressure marking requirement. F ECE (not EEC) type approval mark and number. G North American Dept of Transport compliance symbols and identification numbers. H Country of manufacture. As well as all that, you might also find the following embossed in the rubber tyre marking: . The temperature rating - an indicator of how well the tyre withstands heat buildup. "A" is the highest rating; "C" is the lowest. . The traction rating - an indicator of how well the tyre is capable of stopping on wet pavement. "AA" is the highest rating; "C" is the lowest. . The tread-wear rating - a comparative rating for the useful life of the tyre's tread. A tyre with a tread-wear rating of 200, for example, could be expected to last twice as long as one with a rating of 100. Tread-wear grades typically range between 60 and 600 in 20-point increments. It is important to consider that this is a relative indicator, and the actual life of a tyre's tread will be affected by quality of road surfaces, type of driving, correct tyre inflation, proper wheel alignment and other variable factors. In other words, don't think that a tread-wear rating of 100 means a 30,000 mile tyre. Encoded in the US DOT information (G in the tyre marking above) is a two-letter code that identifies in detail where the tyre was manufactured. In other words, what factory and in some cases, what city it was manufactured in. It's the first two letters after the 'DOT' - in this case "FA" denoting Yokohama. This two-letter identifier is worth knowing in case you see a tyre recall on the evening news where they tell you a certain factory is recalling tyres. Armed with the two-letter identifier list, you can figure out if you are affected. It's a nauseatingly long list, and I've not put it on this page. But if you click here it will popup a separate window with just those codes in it.
Another useful resource, which I discovered by myself is CARiD.com. Huge selection of tires, plenty of useful videos and articles and the most accurate wheel & tire fitment database in the industry: http://www.carid.com/tires.html You just select the year, make and model of your vehicle, choose the right diameter, offset, backspacing, and bolt pattern and wait for your new set of tires to arrive! ADDITIONAL MARKINGS In addition to all of the above, here is a comprehensive list of other markings you can find on your sidewall. This section is hidden by default because it takes up a lot of space on the page. the additional markings section. OE MANUFACTURER LETTERS In the same way that Porsche specifies N-rated tyres (see later), there's even more markings on the sidewall of a tyre that can denote tyres fitted as original equipment (OE) to various makes of vehicle. In some cases, the 'preferred' OE tyres are slightly different than the same-named tyres without the OE specification. For example on some Honda SUVs, the tyres that are stamped with 'DZ' have a lower rolling resistance tread pattern than those that aren't. In true "Keeping the customer confused" fashion, you'll notice that (F) is not the same as (f). Go (f)igure. The following table shows all the letters assigned to OE tyres for various manufacturers. This section is hidden by default because it takes up a lot of space on the page. the OE manufacturer letters section. DOT CODES AND THE 6-YEAR SHELF LIFE
As part of the DOT code (G in the tyre marking above), there is a tyre manufacture date stamped on the sidewall. Oddly this code is sometimes only one one sidewall so you might need to get under your car and look at the inward-facing side of the tyre. Take a look at yours - there will be a three- or four-digit code. This code denotes when the tyre was manufactured, and as a rule-of-thumb, you should never use tyres more than 6 years old. The rubber in tyres degrades over time, irrespective of whether the tyre is being used or not. When you get a tyre change, if you can, see if the tyre place will allow you to inspect the new tyres first. It's not uncommon for these shops to have stuff in stock which is more than 6 years old. The tyre might look brand new, but it will delaminate or have some other failure within weeks of being put on a vehicle. Reading the code. The code is pretty simple. The three-digit code was used for tyres manufactured before 2000. So for example 1 7 6 means it was manufactured in the 17th week of 6th year of the decade. In this case it means 1986. For tyres manufactured in the 90's, the same code holds true but there is a little triangle after the DOT code. So for this example, a tyre manufactured in the 17th week of 1996 would have the code 176 After 2000, the code was switched to a 4-digit code. Same rules apply, so for example 3 0 0 3 means the tyre was manufactured in the 30th week of 2003. DOT tire code CHECK YOUR SPARE I had a reader email me about the age code and he pointed out that it's wise to check your spare tyre too. In his case, he had an older vehicle but his running tyres were all nice and fresh. It was his spare that was the problem - it had a date code on it of 081 meaning it was manufactured in the 8th week of 1991. At the time of writing, that was a 16 year old tyre. So you've been warned - if you're driving an older car, check the date code of your spare. If you get a flat and your spare is gently corroding in the boot (or trunk), it won't do you much good at all. DOT AGE CODE CALCULATOR The calculation built in to this page is up-to-date based on today's date. If the DOT age code on your tyres is older than this code, change your tyres. DOT AGE CODE: 3309 Interesting note : in June 2005, Ford and GM admitted that tyres older than 6 years posed a hazard and from their 2006 model year onwards, started printing warnings to this effect in their drivers handbooks for all their vehicles. TAKE THE AGE CODE SERIOUSLY : A TALE OF CAUTION A reader contacted me in 2010 with a tale of caution regarding the manufacturing age code on old tyres.
In August 2010, I bought a classic 1976 Mercedes with only 30,000 miles on it. The seller (who was only the second owner) warned me that he thought that the Michelin XVS tyres were pretty old (the spare was unused). I was aware of the dangers of old tyres from reading your tyre bible, but it was a Sunday and the tyres are an unusual size (205/70R14) and were not readily available. I thought that I'd risk the trip back home (250 miles), but that I'd need to get new tyres ASAP. Unfortunately, one of the tyres didn't last that long, and failed at 70 MPH (see photo, note my skidmarks). It turned out that the tyres were date-stamped from week 30, 1986(!), so the advice about old tyres is indeed true! For the record, I ordered new tyres and had the minor body damage repaired, and all is well with the car now. Stephen W, Dublin, Ireland. THE E-MARK
Item F in the tyre marking diagram above is the E-mark. All tyres sold in Europe after July 1997 must carry an E-mark. The mark itself is either an upper or lower case "E" followed by a number in a circle or rectangle, followed by a further number. An "E" (upper case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. An "e" (lower case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of Directive 92/33/EEC. The number in the circle or rectangle denotes the country code of the government that granted the type approval. 11 is the UK. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tyre size and type. TYRE SIZE NOTATIONS Okay, so you look at your car and discover that it is shod with a nice, but worn set of 185-65HR13's (from the tyre marking). Any tyre mechanic will tell you that he can replace them, and he will. You'll cough up and drive away safe in the knowledge that he's just put some more rubber on each corner of the car that has the same shamanic symbols on it as those he took off. So what does it all mean? tire size markings This is the ratio of the This is the diameter height of the tyre ininches of the rim of the This is the width in mm of sidewall, (section height), This tells you that the wheel that the tyre has the tyre from sidewall to expressed as a tyre is a radial been designed to fit sidewall when it's percentage of the width. construction. Check on.Don't ask me why unstressed and you're It is known as the aspect This is out tyre tyre sizes mix imperial looking at it head on (or ratio. In this case, 65% of thespeed construction if you and metric top-down). This is known 185mm is 120.25mm - ratingof the want to know what measurements. They as the section width. the section height. tyre. that means. just do. Okay? More recently, there has been a move (especially in Europe) to adjust tyre designations to conform to DIN. This is the German Institute for standardisation - Deutsches Institut fuer Normung, often truncated to Deutsche Industrie Normal. DIN sizing means a slight change in the way the information is presented to the following:
Section width Aspect ratio Radial Rim diameter Load index Speed rating ULTRA HIGH SPEED TYRE SIZE NOTATIONS There is a subtle difference in the notation used on ultra high speed tyres, in particular motorcycle tyres. For the most part, the notation is the same as the DIN style described above. The difference is in the way the speed rating is displayed. For these tyres, if the speed rating is above 149mph, then a 'Z' must appear in the dimension part of the notation, as well as the actual speed rating shown elsewhere. The 'Z' is a quick way to see that the tyre is rated for over 149mph. Section width Aspect ratio 149+ mph rated Radial Rim diameter Load index Speed rating CLASSIC / VINTAGE / IMPERIAL CROSSPLY TYRE SIZES What ho. Fabulous morning for a ride in the Bentley. Problem is your 1955 Bentley is running on 7.6x15 tyres. What, you ask, is 7.6x15? Well it's for older vehicles with imperial measurements and crossply tyres. Both measurements are in inches - in this case a 7.6inch tyre designed to fit a 15inch wheel. There is one piece of information missing though - aspect ratio. Aspect ratios only began to be reduced at the end of the 1960s to improve cornering. Previously no aspect ratio was given on radial or crossply tyres. For crossply tyres, the initial number is both the tread width and the sidewall height. So in my example, 7.6x15 denotes a tyre 7.6 inches across with a sidewall height which is also 7.6 inches. After conversion to the newer notation, this is the equivalent to a 195/100 15. If you're plugging numbers into the tyre size calculator lower down this page, I've included an aspect ratio value of 100 for imperial calculations. Note: I put 195/100 15 instead of 195/100R15 because technically the "R" means radial. If you're trying to get replacement crossply tyres, the "R" won't be in the specification. However if you're trying to replace your old crossply tyres with metric radial bias tyres, then the size does have the "R" in it. Here is a javascript calculator to turn your imperial tyre size into a radial metric tyre size: Your imperial tyre size: x 7.6 15 Equivalent standard tyre size is : /100 R
For quick reference, you could also try my vintage tyre size conversion table which lists a lot of common sizes along with their modern counterparts. classic tire sizes CLASSIC / VINTAGE RADIAL TYRE SIZES Remember above that I said aspect ratios only started to come into play in the 1960s? Unlike the 100% aspect ratio for crossply tyres, for radial tyres, it's slightly different - here an aspect ratio of 80% is be assumed. So for example, if you come across on older tyre with 185R16 stamped on it, this describes a tyre with a tread width of 185mm and a sidewall height which is assumed to be 80% of that; 148mm. The question of the aspect ratio for radial sizes has been the subject of a lot of email to me. I've had varying figures from 80% up to 85% and everyone claims they're right. Well one reader took it to heart and did some in-depth research. It seem there is actually no fixed standard for aspect ratio when it is not expressly stated in the tyre size. Different manufacturers use slightly different figures. The english MOT (road-worthiness test) manual states: Unless marked otherwise, "standard" car tyres have a nominal aspect ratio of 82%. Some tyres have an aspect ratio of 80%. These have "/80" included in the size part of the tyre marking e.g. 165/80 R13. Note: Tyres with aspect ratios of 80% and 82% are almost identical in size and can be safely mixed in any configuration on a vehicle. See http://www.motuk.co.uk/manual_410.htm for the online version. If you're plugging vintage radial numbers into the tyre size calculator, I've included aspect ratios of 80 and 82 for these calculations. ALPHA NUMERIC LOAD-BASED TYRE SIZES FOR VINTAGE CARS Picture credit: Jensen Intercepter Club
On some 60's and 70's era vintage vehicles, (for example the Jensen Interceptor), the tyre sizes were denoted as ER70VR15. The '70' refers to the section height as you might expect, and the '15' is the wheel dimension, but on first inspection there appears to be no section width. Actually there is, but it's in yet another odd format. In this case, the first letter is the thing to look at. The letter itself has no direct equivalent to modern dimensional sizes but instead relates to load index; the higher the letter the more load it can carry. With vintage tyres, higher loads translated into bigger tyres, so the close approximations between old load and new size these days are: C = 185 D = 195 E = 205 F = 215 G = 225 H = 235 etc. In this example then, ER70VR15 means 205/70 R15 with a 'V' speed rating. Whilst many of the latter Interceptors were technically capable of 140mph, the aerodynamic behaviour would have you quickly backing off to about 120mph so frankly that 'V' rating is a little optimistic. If you're looking to replace tyres for this type of vehicle, an 'H' speed rated tyre is the better choice, and it's cheaper. For those of you reading this in the colonies, an example vehicle from this era is the Chevy Nova which had E78-14 tyres. (In this case, there was no letter 'R' meaning these were cross-ply tyres, not radials). The equivalent size in modern notation would be 205/78 R14. The following converter will give you a rough idea of the equivalent metric tyre size for a given alpha numeric tyre size: Your alphanumeric tyre size: R / R E 78 14
For quick reference, you could also try my vintage tyre size conversion table which lists a lot of common sizes along with their modern counterparts. METRIC TYRE SIZES AND THE BMW BLURB
Fab! You've bought a BMW 525TD. Tyres look a bit shoddy so you go to replace them. What the....? TD230/55ZR390? What the hell does that mean? Well my friend, you've bought a car with metric tyres. Not that there's any real difference, but certain manufacturers experiment with different things. For a while, (mid 1990s) the 525TD came with arguably experimental 390x180 alloy wheels. These buggers required huge and non-conformal tyres. I'll break down that classification into chunks you can understand with your new-found knowledge: TD - ignore that. 230 = cross section 230mm. 55 = 55% sidewall height. Z=very high speed rating. R390=390mm diameter wheels. These are the equivalent of about a 15.5" wheel. There's a nice standard size for you. And you, my friend, have bought in to the long-raging debate about those tyres. They are an odd size, 180x390. Very few manufacturers make them now and if you've been shopping around for them, you'll have had the odd heart-stopper at the high price. The advice from the BMWcar magazine forum is to change the wheels to standard sized 16" so there's more choice of tyres. 215-55R16 for example. The technical reason for the 390s apparently is that they should run flat in the event of a puncture but that started a whole debate on their forum and serious doubts were expressed. You've been warned... If you're European, you'll know that there's one country bound to throw a spanner in the works of just about anything. To assist BMW in the confusion of buyers everywhere, the French, or more specifically Michelin have decided to go one step further out of line with their Pax tyre system. See the section later on to do with run-flat tyres to find out how they've decided to mark their wheels and tyres. Metric tire sizes LAND ROVERS AND OTHER OFF-ROAD TYRE SIZES
On older Land Rovers (on the LWB/110 vehicles and many "off-roaders"), you'll often find tyres with a size like 750x16. This is another weird notation which defies logic. In this case, the 750 refers to a decimalised notation of an inch measurement. 750 = 7.50 inches, referring to the "normal inflated width" of the tyre - i.e. the external maximum width of the inflated, unladen tyre. (This is helpfully also not necessarily the width of the tread itself). The 16 still means 16 inch rims. Weird eh? The next question if you came to this page looking for info on Land Rover tyres will be "What size tyre is that the equivalent of in modern notation?". Simple. It has no aspect ratio and the original tyres would likely be cross-ply, so from what you've learned a couple of paragraphs above, assume 100% aspect ratio. Convert 7.5inches to be 190mm. That gives you a 190/100 R16 tyre. (You could use the calculator in the section on Classic / vintage / imperial crossply tyre sizes above to get the same result.) Generally speaking, the Land Rover folks reckon a 265/65R16 is a good replacement for the "750", although the tread is slightly wider and might give some fouling problems on full lock. It's also 5% smaller in rolling radius so your speed will over-read by about 4mph at 70mph. If you can't fit those, then the other size that is recommended by Landrover anoraks is 235/85R16. On Discoveries, Range Rovers, or the SWB Defenders/Series land rovers you'll find "205" tyres, denoting 205mm x 16 inches. The 205 type tyres can generally be replaced with 235/70R16 or 225/75R16. The 235 is a wider tyre and the general consensus in Land Rover circles is that it holds the road better when being pushed. If you're really into this stuff, you ought to read Tom Sheppard's Off Roader Driving (ISBN 0953232425). It's a Land Rover publication first published in 1993 as "The Land Rover Experience". It's been steadily revised and you can now get the current edition from Amazon. I've even helpfully provided you with this link so you can go straight to it.... LT (LIGHT TRUCK) IMPERIAL TYRE SIZES Confused yet? Okay how about this: 30x9.5 R15 LT or LT30x9.5/15. Yet another mix- and-match notation, this time for (amongst other things) light truck classification tyres. All the information you need to figure out a standard size is in there, but in the usual weird order. In this case the 30 refers to a 30 inch overall diamter. The 9.5 refers to a 9.5 inch wide tread. The R15 refers to a 15 inch diameter wheel. In order to figure out the closest standard notation, you know the tread width which (in this example) is 9.5 inches or 240mm. The sidewall height is the overall height minus the wheel diameter all divided by 2. So 30 inches minus 15 inches, which gives you 15 inches. Half that to get 7.5 inches and that's the sidewall height - 190mm. Remember the section value is a percentage of the tread width - in this case 190mm/240mm gives us a section of 80% (near enough). So the standard size for 30x9.5R15 works out to be 240/80R15. In truth you can barely find a tyre that size so most off-roaders with that sort of tyre size go for 245/70R15 which is more common. For your convenience, another calculator then. Your LT tyre size: x R 30 9.5 15 Equivalent standard tyre size is : / R
Light truck tires PORSCHE N-RATED TYRES
Porsche designs and manufacturers some of the highest performance cars in the world (with the exception of the butt-ugly Cayenne). All this design and performance is worth nothing if you put cheap Korean tyres on your Porsche, and because of that prospect, Porsche introduced the N rating or N specification system. In order for a manufacturer to be an OE (original equipment) supplier of tyres for Porsches, they must work with the Porsche engineers at the development and testing stage. They concentrate on supreme dry-weather handling but they also spend a considerable amount of time working on wet-weather handling. Porsches are typically very tail-heavy because of the position of the engine relative to the rear wheels, and with traction control off, it's extremely easy to spin one in the wet. Because of this, Porsche specify a set of wet-grip properties which is way above and beyond the requirements of any other car manufacturer. OE tyres for Porsches must successfully pass lab tests to prove that they would be capable of adequately supporting a Porsche at top speed on a German Autobahn. Once the lab tests are done, they must go on to track and race tests where prototypes are evaluated by Porsche engineers for their high-speed durability, uniformity and serviceability. If they pass all the tests, Porsche give the manufacturer the go-ahead to put the car tyres into production and then they can proudly claim they are an N-rated Porsche OEM (Original Equipment Modifier). The N-ratings go from 0 (zero) to 4, marked as N-0, N-1 etc. This N-rating, stamped into a tyre sidewall, clearly identifies these tyres as having gone through all the nauseating R&D and testing required by Porsche as described above. The number designates the revision of the design. So for a totally new design, the first approved version of it will be N-0. When the design is improved in some way, it will be re-rated as an N-1. If the design changes completely so as to become a totally new tyre, it will be re-rated at N-0. If you've got a Porsche, then you ought to be aware that as well as using N-rated tyres, you ought to use matching tyres all around because many Porsches have different sizes tyres front and rear. So for example if you have a Porsche with N-3 rated tyres and the rear ones need replacing but the model has been discontinued, you should notget N-0's and put them on the back leaving the old N-3's on the front. You should replace all of them with the newer-designed re-rated N-0 tyres. But then you own a Porsche so you can certainly afford four new tyres.... One final point. You may go into a tyre warehouse and find two tyres with all identical markings, sizes and speed ratings, but one set has an N-rating. Despite everything else being the same, the non-N-rated tyres have not been certified for use on a Porsche. You can buy them, and you can put them on your car, but if you stuff it into the armco at 150mph, Porsche will just look at you and with a very teutonic expression ask why you didn't use N-rated tyres. Porsche tires
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LIES, DAMN LIES AND SPEED RATINGS All tyres are rated with a speed letter. This indicates the maximum speed that the tyre can sustain for a ten minute endurance without coming to pieces and destroying itself, your car, the car next to you and anyone else within a suitable radius at the time. Max Speed Capability Max Speed Capability Speed Symbol Km/h MPH Speed Symbol Km/h MPH L 120 75 S 180 113 M 130 81 T 190 118 N 140 87 U 200 125 P 150 95 H 210 130 Q 160 100 V 240 150 R 170 105 W 270 168 Y 300 186 ZR 240+ 150+ 'H' rated tyres are the most commonplace and widely used tyres, having replaced 'S' and 'T' ratings. Percentage-wise, the current split is something like this: S/T=37%, H=63%, V=8%. Certain performance cars come with 'V' or 'ZR' rated tyres as standard. This is good because it matches the performance capability of the car, but bad because you need to re-mortgage your house to buy a new set of tyres. A note on the ZR rating: most speed ratings designate the speed that should not be exceeded. For example W-rated tyres are rated up to 270km/h. ZR-rated tyres, by comparison, are theoretically rated for anything over 240km/h. This is why the Bugatti Veyron was shod with ZR-rated tyres for the world record speed run of 431km/h when Top Gear drove it at the VW Ehra-Lessien test track. Although to be honest, at that speed the tyres only lasted for 8 minutes. UTQG RATINGS The UTQG - Uniform Tyre Quality Grade - test is required of all dry-weather tyres ("snow" tyres are exempt) before they may be sold in the United States. This is a rather simple-minded test that produces three index numbers : Tread life, Traction and Temperature. . The tread life index measures the relative tread life of the tyre compared to a "government reference". An index of 100 is equivalent to an estimated tread life of 30,000 miles of highway driving. . The traction test is a measure of wet braking performance of a new tyre. There is no minimum stopping distance, therefore a grade "C" tyre can be very poor in the wet. . The temperature test is run at high speeds and high ambient temperatures until the tyre fails. To achieve a minimum grade of "C" the tyre must safely run at 85mph for 30 minutes, higher grades are indicative of surviving higher speeds (a rating of "B" is, for some reason, roughly equivalent to a European "S" rating, a rating of "A" is equivalent to an "H" rating.) There are some exceptions: Yokohama A008's are temperature rated "C" yet are sold as "H" speed rated tyres. These UTQC tests should be used only as a rough guide for stopping. If you drive in the snow, seriously consider a pair of (if not four) "Snow Tyres". Like life, this tyre test is entirely subjective. LOAD INDICES The load index on a tyre is a numerical code associated with the maximum load the tyre can carry. These are generally valid for speed under 210km/h (130mph). Once you get above these speeds, the load-carrying capacity of the tyre decreases and you're in highly technical territory the likes of which I'm not going into on this page. (Mostly because I don't understand it). The table below gives you most of the Load Index (LI) values you're likely to come across. For the sake of simplicity, if you know your car weighs 2 tons - 2000kg - then assume an even weight on each wheel. 4 wheels at 2000kg = 500kg per wheel. This is a load index of 84. The engineer in you should add 10% or more for safety's sake. For this example, I'd probably add 20% for a weight capacity of 600kg - a load index of 90. Generally speaking, the average car tyre is going to have a much higher load index than you'd ever need. It's better to have something that will fail at speeds and stress levels you physically can't achieve, than have something that will fail if you nudge over 60mph with a six pack in the trunk. LI kg LI kg LI kg LI kg LI kg LI kg 50 190 70 335 90 600 110 1060 130 1900 150 3350 51 195 71 345 91 615 111 1090 131 1950 151 3450 52 200 72 355 92 630 112 1120 132 2000 152 3550 53 206 73 365 93 650 113 1150 133 2060 153 3650 54 212 74 375 94 670 114 1180 134 2120 154 3750 55 218 75 387 95 690 115 1215 135 2180 155 3875 56 224 76 400 96 710 116 1250 136 2240 156 4000 57 230 77 412 97 730 117 1285 137 2300 157 4125 58 236 78 425 98 750 118 1320 138 2360 158 4250 59 243 79 437 99 775 119 1360 139 2430 159 4375 60 250 80 450 100 800 120 1400 140 2500 160 4500 61 257 81 462 101 825 121 1450 141 2575 161 4625 62 265 82 475 102 850 122 1500 142 2650 162 4750 63 272 83 487 103 875 123 1550 143 2725 163 4875 64 280 84 500 104 900 124 1600 144 2800 164 5000 65 290 85 515 105 925 125 1650 145 2900 165 5150 66 300 86 530 106 950 126 1700 146 3000 166 5300 67 307 87 545 107 975 127 1750 147 3075 167 5450 68 315 88 560 108 1000 128 1800 148 3150 168 5600 69 325 89 580 109 1030 129 1850 149 3250 169 5800