fasttech / TECH / CYLINDER HEADS / fasttech HEADHEAD MASTER Pay attention as Stu offers up a masterclass in what you need to know about cylinder heads.

related to its ability to pump air almost everywhere and yet retains will develop its peak power (see in great volumes, and the limiting sensible fuel economy, driveability Fast Ford issues 245 and 246 factor to how much air can be and idle characteristics? for more in-depth camshaft and pumped is related to the pathway I would say that over 90 per cent timing information). Don’t forget into and out of the pump. of us, myself included, want the that the airfl ow capability of the In the case of an engine this is latter, so before you take a Dremel head and the velocity of the everythingeverything ffromrom tthehe aairir fi llterter ttoo to your cylinder head I suggest you airfl ow itself are all factors that the next few thethe iinletnlet vvalve,alve, andand converselyconversely grab a coffee and absorb a little are taken into account when OVER months I intend everythingeverything ffromrom tthehe eexhaustxhaust vvalvealve more information on what does designing camshafts, so be aware to cover some of the more old- toto tthehe eexhaustxhaust bbackack bbox,ox, bbutut ttodayoday andand ddoesoes nnotot wworkork iinn tthehe wworldorld ooff that modifying the head too much school yet fundamental tuning wewe aarere dealingdealing withwith thethe ccylinderylinder cylindercylinder hheadead pportingorting aandnd ddesign.esign. can also mean the camshaft is no processes that some modern headhead aandnd iitsts aassociatedssociated iitems.tems. Let’sLet’s looklook aatt tthehe ffundamentals.undamentals. longer suitable. tuners and magazines seem to So,So, ifif wewe increaseincrease thatthat airair volumevolume have forgotten all about, since the pumpingpumping aabilitybility tthenhen wwee iincreasencrease PORTPORT FLOWFLOW VSVS AIRFLOW advent of electronic tuning trickery. ourour ppotentialotential ppowerower ooutput.utput. SSimpleimple MIXTUREXTURE VELOCVELOCITYTY REQUREQUIREMENTS I’d like to start this series with isn’tisn’t iit?t? WeWe eestablishedstablished eearlierarlier tthathat aann NaturallyNaturally the fl ow requirementrequirement the good old-fashioned cylinder ActuallyActually nno,o, sadlysadly itit isn’t.isn’t. engine’sengine’s abilityability ttoo fi llll iitsts of an engine incrincreaseseases head and the various modifi cations AlthoughAlthough yyouou wwouldould nnoo ddoubtoubt as its rrevsevs increase.increase. ForFor we can make to it. Any good tuner instantlyinstantly tthinkhink tthathat tthishis mmeanseans example,example, anan engineengine will tell you that the cylinder head biggerbigger pportsorts aandnd itself is the heart of your engine and without a good head on your block you will never get good power no matter what else you do to it, and conversely you will also nevernever ggetet ggoodood ddriveabilityriveability oorr ggoodood digestingdigesting 3300 fuelfuel eeconomyconomy eeither,ither, asas thesethese areare lblb ooff aairir aatt 33000000 allall aaspectsspects mmainlyainly ddictatedictated bbyy tthehe rpmrpm wwillill trytry ttoo ddigestigest 6600 llbb ooff aairir cylindercylinder hhead.ead. TheThe cylindercylinder headhead biggerbigger camscams atat 66000000 rrpm,pm, allall tthingshings bbeingeing eequal.qual. andand iitsts aassociatedssociated iitemstems rreallyeally ddoo mustmust bbee bbetter,etter, inin cylinderscylinders iiss tthehe OneOne tthinghing mmanyany ppeopleeople fforgetorget iiss makemake oorr bbreakreak thethe torquetorque curvecurve thethe rrealeal worldworld thatthat limitinglimiting ffactoractor thatthat tthehe aamountmount ooff ttimeime aavailablevailable and dictate the potential power isn’tisn’t tthehe ccasease bbecauseecause dictatingdictating wwhathat iitsts uultimateltimate toto aactuallyctually fi llll tthehe ccylindersylinders wwithith output of your engine, so let’s variousvarious ddynamicsynamics sstarttart ttoo powerpower ooutpututput wwillill bbe.e. InIn thisthis aair/fuelir/fuel mmixtureixture ddecreasesecreases BEFORE go back to basics as always and taketake ttheirheir ppartart iinn tthehe pproceedingsroceedings normally-aspiratednormally-aspirated (not(not turboturbo proportionatelyproportionately ttoo rrpm.pm. IItt iiss qquiteuite STARTING… examine why exactly the cylinder andand aass aalways,lways, thingsthings areare notnot asas oror ssupercharged)upercharged) form,form, thethe staggeringstaggering wwhenhen yyouou tthinkhink aaboutbout head is so important to our engine. simplesimple aass ttheyhey fi rrstst aappearppear ttoo bbe.e. cylinderscylinders aarere fi lledlled byby thethe ppressureressure itit — aatt 55000000 rrpmpm wwee oonlynly hhaveave The fi rst rule of working on differentialdifferential thatthat isis ccreatedreated whenwhen anan aaverageverage ofof sixsix thousandthsthousandths ofof cars and using tools of any kind is don’t ever skimp on AIR WAYS POWER OR thethe ppistoniston mmovesoves ddownown tthehe a ssecondecond ttoo ggetet tthehe aairir iintonto tthehe decent protection. Goggles, To describe what exactly an DRIVEABILTY? borebore againstagainst anan openopen inletinlet valvevalve cylindercylinder bbeforeefore thethe valvevalve cclosesloses gloves, ear defenders, masks and a set of overalls engine is I always fi nd it best to Big brash ports and cams, while (barring(barring aanyny rramam oror shockshock wavewave again.again. OnceOnce thethe engine’sengine’s airflairfl owow should be in your garage. compare it to an air pump. In often allowing the best top-end tuningtuning eeffects).ffects). TheThe actualactual cylindercylinder demanddemand ooutstripsutstrips tthehe aabilitybility ooff tthehe Use them. When using power tools, reality, all complexities aside, that power fi gure, will invariable fi lling effi ciency is measured and headhead ttoo ddelivereliver iincreasedncreased aairflirfl oow,w, protective gear is essential is exactly what it is — it draws air damage our low-end driveability, expressed in terms of volumetric VEVE ttailsails ooff,ff, asas doesdoes peakpeak power.power. — grinders and welders can make a real mess of your in, develops power with it after the fuel economy and torque. Is that effi ciency (VE). AsAs a qquickuick eexample,xample, ifif a headhead cancan soft skin and bone if you get it wrong. addition of fuel, and then expels it the result you wanted? A dog of an The timing events of the valves fl owow 3300 llbb ooff aairir pperer mminuteinute aandnd tthehe Never work under a car again. This pumping cycle happens engine that goes OK up near the opening and closing is the primary engine at 3000 rpm requires 30 lb without supporting it using Words: Stewart Sanderson axle stands. A car falling on very quickly indeed, but the fact limiter but nowhere else, or did you factor determining the rev range of air per minute it will make 100 you is not something you’ll be remains that the power-producing actually want a good overall engine in which the engine will achieve per cent volumetric effi ciency here laughing about down the pub. capability of the engine is directly that goes better than standard its peak VE and where the engine and possibly its peak torque, but be

0 1 3 0 MARCH 2007 FAST FORD FAST FORD MARCH 2007 0 1 3 1 fasttech / TECH / CYLINDER HEADS / fasttech

to continue fi lling the cylinder, direction and fl ow backwards as SQUISH EFFECT cramming in the air, sometimes the inlet valve is open at this point Something I have seen badly A large, inert volume of air in the inlet is slow to provide a signal Having massive inlet ports can actually lose you to the MAP sensor/airfl ow meter, giving lazy throttle response power, as it slows down speed of the airfl ow above 100 per cent VE as we allowing sometimes less pressure modifi ed many times over the actually compress some air due to in the cylinder than the exhaust years is the squish area of the the piston moving upwards and the port (a gas will always fl ow to the cylinder head. It has often been gas still travelling downwards when point of least resistance). This is destroyed by someone who quite the intake valve closes. not at all helpful as it dilutes our possibly doesn’t even know that it A good example of inertia is incoming fresh mix. This effect is exists, let alone what its purpose when we spin a heavy wheel, usually far worse at low rpm where was. Squish is the term used to maybe on a car or push bike. Once fl ow rates and velocity are at their describe the area of the cylinder we have let go after our spinning lowest due to obvious factors. head that comes into very close movement, the wheel takes no It’s worth bearing in mind that proximity to the piston at top dead more energy to continue spinning, this particular issue is normally centre (TDC). so it should have just stopped made far worse with increased- It’s a known fact that in over 90 when we let go, but it didn’t, did it? overlap, high-performance cams. per cent of engines, a faster burn In fact, if we try to stop it spinning The result is an engine that is slow and a more turbulent mixture are now it resists us. This is inertia. to get on the cam as engine speed obtained when the compression picks up some velocity in the height of the piston is set to take EXHAUSTEXHAUST GASGAS exhaust port, and very poor low- the maximum advantage of the fl at VELOCVELOCITY & INERTIA speed engine operation and bad, quench face of the cylinder head. InIn tthehe eexhaustxhaust pport,ort, mmanyany ooff tthehe sometimes non-existent idle. In other words, if the area samesame cconsiderationsonsiderations applyapply asas Ultimately, both the intake between the fl at face of the head withwith tthehe iinletnlet pports.orts. InIn tthehe eexhaustxhaust and exhaust ports must balance and the piston top is suffi ciently ports, instead of drawing in air fl ow velocity and fl ow capacity to close, as the piston reaches awareaware tthathat tthehe ssameame hheadead wwillill oonlynly drainpipe-sized inlet and exhaust velocity means that the air column and fuel to fi ll the cylinder we are achieve fl exible performance over TDC on the compression stroke, supply 30 lb of air per minute to the tracts and fi t massive combustion is moving faster and this means actually pushing it out with a piston. a broad range of engine speeds. the mixture that occupied the engine, which at 6000 rpm requires chamber-fi lling valves. information will be relayed more Maintaining a good gas velocity This is a necessity in a road-based area over the piston is forced at the combustion chamber is literally Detonation almost always begins twice as much to make the same This would create an engine that accurately to the management. Far here helps to scavenge the cylinder performance engine. We should high speed into the direction of squished into the centre of the in an area other than that where torque as it did at 3000 rpm. All of was useless, it’s unlikely it would more important than this is a totally of spent gases to promote good always maximize the effi cient use the advancing fl ame front. The chamber by the rising piston. the main fl ame front is initiated. these airfl ow issues are dealt with even start and idle. Why? Because different dimension that has now cylinder fi lling of fresh air/fuel charge, of the port to achieve the required benefi ts of this are faster burn A second benefi t of this With a fl at-topped piston, the area by the cylinder head (obviously velocity is as important as volume. opened up to us — gas inertia. because don’t forget we cannot fi ll a gasfl ow, instead of simply making and greater turbulence at the time squish phenomenon is that the opposite the spark plug in the ignoring any inlet hardware cylinder with 100 per cent fresh fuel bigger ports to give ultimate high- of combustion. This is called the engine’s mechanical resistance to quench area is prime detonation restrictions that may exist such INLET VELOCITY INLET GAS INERTIA and air, if 15 per cent of the old burnt end bhp. squish effect. In a nutshell, the fuel/ detonation is improved when close territory. If this area is suffi ciently as throttle body, airbox etc). It’s a sad fact that as port volume Basic physics tells us that a body in garbage is still in there, can we? air mixture at the outer edges of piston-to-head clearance is utilised. tight, the ability for it to detonate So we know that large amounts increases, velocity decreases. A motion (in this case, the air column) If we look at an exhaust port with SWIRL & TUMBLE reduces since the combustion of airfl ow are paramount to high huge port between the throttle will build momentum and will poor fl ow velocity due to excessive After dealing with the port’s fl ow at the desired fl ame front occurs engine speed performance and body and the inlet valve will create want to keep moving in the same port size, we will see that we will capacity and of course velocity, the quicker due to the squish effect thus high bhp output. However, if a proportionally large volume of air. direction, even as the force acting usually have a large, slow-moving next logical step is to recognise and lessens the time for heat rise The actual motion of air through the on it is removed. It’s called inertia. pocket of burnt gas literally slowed the presence of externally-induced in the mixture at the far end of the inlet tract to the cylinder is dictated In the case of the air within the down to almost stationary awaiting mixture motion. The important part chamber. Furthermore, the thin by the volume of the cylinder made port, the force acting on the air the next push of gas to shove it into here is to recognise the fact that the section at the squish area exposes available by the piston moving down column is the pressure differential the manifold. Why? As the piston mixture will fl ow through the port only the small volume of mixture the bore. So the nearer we get to in the cylinder as the piston moves reached the top of the exhaust and into the cylinder in a very un- to an equally high surface area, matching the two volumes up, the down and the pressure acting stroke and then began to slow uniform fashion, and will normally diminishing the heat rise in this slower our gas speed will be on the upon it from the atmosphere. massively ready for its direction enter in a rotational fashion. part of the mixture. cylinder fi lling event. When the piston slows as it change, the lack of inertia in our This is best compared to a plug As an example, imagine the reaches the bottom of the cylinder gas (due to the large port) meant and drain in a sink. When you pull the THEORY TEST same scenario using a pint glass at the end of the induction stroke, the mixture also stopped and in plug, the water in the sink doesn’t So, there you have it, I hope that and a straw. You have 3 seconds good port velocity is helpful some cases, it can actually reverse just pour down the plug hole and out has given you a small insight into to fi ll the pint glass from a tap of the drain like it was poured from a what goes into the modifying of a using a straw. The speed the water Correct valve size is crucial to good driveability pan does it? No, because it also has cylinder head, or at least the theory travelled through the straw to the as well as outright performance to fl ow down a port of sorts, it exits behind the modifi cations and why glass would be very high. However, in a rotational motion following the you cannot simply take a Dremel if you perform the same test but perimeter of the bore. to a cylinder head and make use a hose pipe to fi ll the glass, the Tumble is a little harder to put everything bigger as many home actual speed of the water would be into words, but imagine pouring tuners do. a lot lower, due to shifting far more a liquid quickly into a wine glass volume per second. It’s the same down one side, and the liquid principle in an engine, but we are quickly rises up the opposite wall talking thousandths of a second, so of the wine glass then almost free WHAT IS VE? the speeds are far higher. falls into the centre of the glass, It’s also important to know that this is what I call port tumble. This is the ratio between the since the large column of air in Many factors can infl uence mechanical volume available the inlet tract is the only means by tumble but the most dominant within the cylinder, and the An engine’s ability to fi ll which the cylinder communicates factor is the intake valve’s position volume of mixture the cylinder its cylinders dictates what with an engine’s MAP sensor or in the combustion chamber when actually ingests. For example, if power it will produce airfl ow meter, a large, lazy volume looked at in relation to the intake the cylinder is completely fi lled of air in the port is slow to provide port’s centreline. Many older with fuel/air, the volumetric achieving large fl ow fi gures was all a signal to your management about combustion chamber designs that effi ciency is 100 per cent. If it is that we needed to create a good- what exactly is happening and placed valves around the perimeter only 70 pe cent fi lled with fuel/ quality cylinder head, port design what our fuel requirements are. The of the chamber induced mixture air we say the engine at that would not represent a signifi cant end result of this is a lazy throttle tumble. Modern inline valves tend point has a volumetric Squish effect is where the head face and piston top are effi ciency of 70 per cent. engineering challenge at all. We response and an engine that to promote far more swirl, which, very close at TDC giving a faster, better mixture burn would simply bore in some huge feels fl at. Conversely, a high port overall, is far better.

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CAN WE DIY?

The previous pages cover the majority Removing sharp edges in the the valve seat areas. Sharp but a good smooth fi nish on the Please remember, a basic porting Removing casting marks from of the key elements that need careful valve guide boss and seat edges create large amounts of exhaust ports can be benefi cial in job does not attempt to correct any the ports is well worth doing consideration before you start boring areas speeds up airfl ow turbulence as they work just like a resisting carbon build up which does design or engineering defi ciencies out your cylinder head and fi tting the ramp to the high-speed air, forcing it of course slowly cut down our present in the casting itself, and is biggest valves known to man. to tumble and crash into walls, available port fl ow. intended purely to improve upon the So what can you do on a DIY level slowing its progress massively. All existing design without really that will improve things before you have areas should be nicely radiused for BASIC PORTING changing anything dramatic. to give the head to a professional? Well, maximum smooth progress of the Whilst very time consuming, basic As soon as you try to change the basic cylinder head porting will improve high-speed gas. porting isn’t actually hard work. I way things work in a large way, such the performance of any production would allow around 8 hours for an as changing port angles or changing cylinder head by simply removing the CASTING average DIY mechanic to do a decent valve sizes, you really are beyond the fl aws that are present due to the ROUGHNESS job on the average four-cylinder, 16- scope of a DIY basic head port and procedures used to manufacture these The castings on an OEM head will be valve head and thus produce a decent should be enlisting the help of large castings in a mass-production quite rough, and its worth cleaning head with no nasty casting marks, professionals who do this for a living. environment. Most of the work in a them up so they become smoother. A burrs lumps or sharp edges to ruin our basic porting project is focused on mirrormirror fi nishnish isis pointlesspointless andand cancan inin gasgas fl ow.ow. You can do basic head mods reducing the restrictions and factfact bebe detrimentaldetrimental onon thethe inletinlet side,side, yourself. But stuff like fi tting compromises have to be made with: larger valves, leave to the pros CASTING MARKS AND RIDGES These are present on port fl oors, roofs and walls and are caused by the casting process. Such items ruin the smooth fl ow of gas and create turbulence and swirl as well as taking up precious room in the tract. A simple out or break a waterway or oil gallery. fl ap wheel can often remove these If you do, the head is scrap. issues to a suitable standard. SHARP EDGES STEPS FROM These can be found in the valve guide MANIFOLD TO TRACT bossboss areaarea andand inin mostmost casescases thethe toptop ofof These steps are simply there due to a mismatch in port size and manifold size or position, and it’s well worth matching the two up so the fl ow from manifold to head (see pic on the right), or indeed head to manifold on the exhaust side, is restriction and obstacle free for your high-speed gas. A Dremel with a decent cutter is needed here, and of course you need to be very careful not to cut too much

TESTING

IfIf youyou don’tdon’t engine,engine, thethe massmass ofof thethe fuelfuel inin thethe worldworld experienceexperience worksworks bestbest inin Dyno testing is the only sure-fi re way to testtest onon a dynodyno air,air, youryour pistonpiston crowncrown conficonfi guration,guration, thisthis arenaarena andand that’sthat’s whywhy I suggestsuggest fi nd out if your head mods have worked you will never really know what the rod/stroke ratio, the piston beyond a basic port clean-up you gains you have made, or indeed velocity, engine rpm and intake entrust your head to a pro with a where you have lost out. A fl ow manifold tuning characteristics, to lot of experience with your bench is ideal to study and test what name only a few. particular head. you have done to the airfl ow This does not discount the validity characteristics, but any professional of fl ow testing and with some simple with fl ow bench and dyno mathematical equations, an NEXT MONTH experience will tell you that once accurate prediction of engine Vital knowledge about exhaust you bolt it onto an engine it all performance can be derived from it, manifolds and systems means very little anyway as fl ow but never assume the fl ow bench bench data often doesn’t relate to has proved your head will work, engine performance in any way often what a perfectly educated shape or form. man thinks is right will prove to be CONTACT Beyond frictional fl ow losses, totally and utterly wrong. other factors affect airfl ow in an Airfl ow still hides itself very well Stewart Sanderson co-owns engine and cannot be duplicated by behind a mask of invisibility and Motorsport Developments fl ow bench testing. These are air even the motor manufacturing in Blackpool: density, thermal transfer of heat to giants’ own scientists still struggle 01253 508400 the incoming charge from the to get their head ports right. Real- www.remapping.co.uk

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