Wayne Ward explains the crucial role played by exhaust systems in helping to maximise the performance of race engines Piping hotMEDIA.

espite what some people in the race engine world may is to remove the burnt gases to a more convenient location. However, think, the subject of exhaust systems is a surprisingly its use as a performance development tool is considerable and it has interesting one. They have a critical bearing on the a critical bearing on the shape of the torque curve as well as affecting performance of the engine, where they play an extremely POWERpeak power. Dimportant role in the engine’s gas exchange processes by Let us briefly consider a simple single-cylinder, four-stroke controlling unsteady gas dynamics. engine with a simple exhaust pipe. A pressure (compression) In the early days of internal combustion engines, this wave generated at exhaust valve opening travels the length role was not clearly understood; exhaust systems were of the exhaust pipe until it meets an expansion in area used simply as a duct to transfer the exhaust gas to a (that is,ONLINE an open end, or a suddenly divergent section), more convenient location before expelling it into the at which point a rarefaction wave is reflected atmosphere. In the early 20th century, researchers suchHIGH back toward the exhaust valve. The easy point to as Morse, Boden and Schecter (1) studied the strong REPUBLISHEDremember here is that when a wave of any kind effect that exhaust geometry has on engine performance. ORcomes to the open end of a tube, it is reflected back Today, it is accepted that the exhaust geometry must be in the opposite sense – that is, a compression wave optimised for a race engine to be effective. produces a reflected rarefaction wave, and vice versa. For highly optimised engine installations,OF as we might BE When a wave hits a closed end of a pipe, however, it is expect to find in Formula One, the exhaust system design reflected back in the same sense, so a compression wave is has been used not only to improve engine performance but reflected back as a compression wave. also to influence vehicle performance, and to a surprising The timing of the returning rarefaction wave is critical. degree. Engineers today “stand on the shoulders of If it arrives just before exhaust valve closing, it ‘sucks’ giants” – to borrow a phrase used by Isaac Newton,TO burnt charge out of the cylinder, aiding scavenging. among others – and by “giants” I mean engineers PRINT If the rarefaction wave arrives at the exhaust valve of yesteryear, such as Hooker et al (2) working for at the wrong time though, it will be reflected and Rolls-Royce in the UK and Pinkel and Voss (3) may, if time permits, result in a compression wave working for Vought-Sikorsky in the US, who in arriving back at the exhaust valve just as it closes, the 1940s discovered the extra thrust that could IN pushing burnt charge back into the cylinder. be developed for aircraft by properlyNOT directing When this happens, the content of the cylinder exhaust flows. when both valves are shut contains a higher In the late 1980s, Norton engineer Brian proportion of residuals. A further effect that also Crighton used the energy of the exhaust gas to cuts performance is that cylinder filling is less draw more cooling air through the engine of efficient in the case where the cylinder contains thePROPERTY Wankel-powered Norton race bikes, using a greater mass of hot gas. a principle similar to that of an ejector pump. When a wave encounters a tapered section More recently, Formula One has used blown rather than a simple opening, the effect is

diffusers to improve downforce at the rear of Fig. 1 – This novel ‘helical’ collector design is for a 4-1 to broaden the range over which the tuning the car. exhaust system; 4-1 collectors are common in many effect is experienced. This is the principle on forms of racing, from club-racing motorcycles to Formula The exhaust system, in terms of pure function, One (Courtesy of BTB Exhausts) which two-stroke expansion chambers operate,

36 FOCUS : EXHAUST SYSTEMS

Fig. 2 – Top Fuel engines open their exhaust valves when the cylinder pressure is about 200 bar (Courtesy of Ron Lewis/Al-Anabi Racing)

MEDIA.

POWER

although two-stroke engines are becoming less common in motorcycle Fig. 3 – This close-up of a Formula One engine shows the racing, where they once dominated. close proximity of the exhaust to In a more sophisticated exhaust system, for example on a four- ONLINEthe cam cover, coil beam and airbox (Courtesy of Cosworth) cylinder engine, the situation with pressure waves is far more complex. When a compression wave arrives at a four-into-oneHIGH collector, it has an effect on all the other cylinders. The superposition REPUBLISHED of all the waves acting in the system has to be considered, and is the OR reason why the different arrangement of pipes into a given collector affects performance. It also explains why linking pipes in different configurations, such as four-two-one or four-oneOF has an effectBE on top- end performance and the character of the torque curve. [Fig. 1 shows a novel four-one collector.] This is not to say though that exhaust tuning is a simple matter of very high mass flow rates, and most of the exhaust system glows red- considering the propagation, reflection and superposition of pressure hot under full-throttle conditions. Radiated exhaust heat can cause waves. Vorum (4) proposes in his papers that theTO engine cylinder and problems for other components – electronics in particular. exhaust pipe act as a Helmholtz resonator during the period wherePRINT the The materials used for exhaust manufacture range from the very valve is open. mundane to some very exotic and correspondingly expensive alloys. In these times of financial restraint in particular, people are often Harsh environment looking for the material that will do the job at minimum cost. The harshest aspect of the working environment for anIN exhaust system In many cases, mild steel will be the material of choice. It has is what is on the inside, as in theNOT extremely hot and high-pressure the advantage of being very widely available at low cost, and is not exhaust gases. In certain cases, namely turbocharged applications, subject to the price fluctuations that can affect more highly alloyed engineers may actually want to encourage combustion within the materials, especially those containing elements traded as commodities. exhaust system. The now common alloy surcharges that reflect current market prices In Top Fuel engines [Fig. 2], the cylinder pressure when the exhaust for some elements are one reason why mild steel has a safe future for valvePROPERTY opens is commonly higher than the peak cylinder pressure in exhaust manufacture. a turbocharged engine of about 200 bar. Car packaging constraints Mild-steel exhausts do need attention though if they are not to often mean there is little cooling airflow to the exhaust, especially in corrode badly. Basic surface treatments such as painting can be very enclosed cars such as single-seaters and endurance racers (Le Mans, effective, but must be re-applied periodically. Other, harder wearing ALMS). Certainly Formula One is a special case [Fig. 3], where tight coatings can be used but at greater expense.

packaging constraints and the attendant lack of cooling conspire with The next step up from mild steel in terms of cost are the austenitic t

37 FOCUS : EXHAUST SYSTEMS

Fig. 4 – This stainless steel system is used on an choice for many forms of racing, including NASCAR. historic sportscar, but stainless remains a popular choice, even in NASCAR (Courtesy of Burns Stainless) Fig. 4 shows a stainless system on an historic sportscar. Titanium is a popular material for exhausts and is used especially widely in motorcycle racing [Figs. 5 and 6], where the mass of the system is well supported. Titanium’s great advantage compared with the other structural exhaust materials is its low density. A typical engineering titanium alloy, Ti-6Al-4V has a density of 4.4 g/cm3, where steels are commonly about 7.8 g/cm3 and many other alloys more dense thanMEDIA. this. Many exhaust companies use low- alloy titanium materials, but one company that specialises in titanium exhausts admits to using more highly alloyed and specially developed ‘alpha’ titanium materials, which include elements such as silicon, aluminium, niobium and iron. Titanium, however, has a couple of disadvantages. The first is that it can become brittle with use, owing to oxidation at high temperature, Fig. 5 – This titanium exhaust system is and can exhibit cracks after a relatively short time. The second from a motorcycle racing application. Bike problem is one of time-dependent strain, or creep. This well-known exhausts are well supported, so titanium finds wide appeal from road bikes to phenomenon is most often demonstrated by measuring strain due to MotoGP. Note link pipes connecting headers a constant load over time, and is particularly associated with high- (Courtesy of Yoshimura) POWERtemperature operation of components.

Exotic materials Superalloys (see below) are often developed for high strength/ stiffness at elevated temperatures as well as resistance to creep. For an unsupported exhaust system,ONLINE such as we might find in Formula One – where exhausts are commonly fastened only to the cylinder head – HIGH titanium is seen as a non-starter owing to creep, especially given the REPUBLISHEDvery high temperature exhaust. Some companies continue to look at titanium materialsOR that are more capable at temperature for exhaust use, but cost is prohibitive (we should remember that titanium is quite stainless steel grades, and again these are widely available in tube happy as an exhaust valve material in many cases). form, being beloved of a number of industriesOF other than automotiveBE Despite these drawbacks of oxidation and creep, titanium is likely exhausts. Stainless steel does not have the same corrosion problems as to remain an attractive option where motorcycles are concerned, and mild steel, but it can cause corrosion problems where it is connected to possibly for other applications too. Titanium can also present some mild steel. For example, a Japanese motorcycle manufacturer lost a lot problems in manufacture, however, with the material prone to sticking of money replacing exhaust systems where it welded mild-steel primary or grabbing during bending and linishing. pipes to stainless collectors. The corrosion at the jointTO appeared rapidly, Superalloys are a class of material based on the more exotic especially on bikes used for short journeys or in cold climates, wherePRINT elements, such as nickel and cobalt. A universally popular type of condensation in the exhaust system is a problem (not to mention rain). superalloy material among the exhaust manufacturers that were While stainless is more expensive than mild steel, such systems canvassed for this article are the Inconel alloys, which are based on are likely to be cheaper in the long term as they are normally more nickel and chromium, with lots of other elements also being used, durable. One problem with stainless exhaust componentsIN can be notably molybdenum and niobium. They have good strength which, their tendency to gall or ‘pick-up’NOT against pieces of the same material. critically, is maintained at high operating temperatures. In addition Primaries can be difficult to remove from mating pipes, they are developed to be creep-resistant. Figs. 7 and 8 on page 40 with ‘slip joints’ sometimes causing problems show Inconel exhaust systems used in Formula One. unless measures such as using a Developed initially for aerospace applications, these types of alloy lubricant are taken. However, are a good example of how motor racing benefits from expensive PROPERTY it remains a very popular materials development undertaken by other industries. In addition to Inconel alloys, other high-temperature

Fig. 6 – This titanium exhaust from a materials have been assessed and can single-cylinder motocross bike has a possibly offer some further advantage chamber attached at two points. Such devices change the torque characteristics of in terms of being able to make a lighter the engine by affecting the pressure waves exhaust. t in the exhaust (Courtesy of Akrapovic)

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RET_ADTEMP.indd 1 08/02/2011 21:22 FOCUS : EXHAUST SYSTEMS

Fig. 7 – The properties of Inconel are so good that exhaust 0.5 mm thick. systems are commonly made from material 0.5 mm (0.020 in) thick. This is a V8 system (Courtesy of SS Tube Technology) One exhaust supplier interviewed for this article admitted to using high-temperature alloys for some exhaust systems based on cobalt, but declined to state which alloy. One point which was made is that in trying to push engines to the maximum, exhaust temperatures are higher and this makes life harder for the exhaust system. CoupledMEDIA. with a desire to run systems for longer and with light weight a serious consideration, this leads people to consider the more expensive materials, perhaps swapping 304 stainless for 321, or swapping 321 stainless for Inconel. Many people believe that exhaust manufacture is simply a matter of putting together the correct pieces of tube and welding them in place, having purchased the tube and bends from an industrial wholesaler. The modern race machine, especially those at the top of Fig. 8 – A beautifully fabricated their particular motorsport, will however have exhaust systems that rely Inconel V8 exhaust system POWERon so much more than welding bought-in components. attached to a jig (Courtesy of Good Fabrication) Beginning with the cylinder head face, you may be lucky enough to be able to buy exhaust flanges in the correct materials, but it is often the case that exhaust flanges will have to be made specially for the engine in question. These can sometimes be as simple as a piece of sheet metal cut to theONLINE correct profile. It is quite common though to find these manufactured by a number of other means, so that the HIGH transition between the flat part of the flange and the exhaust ‘tube’ is REPUBLISHEDmade in solid material rather than a weld fillet. The transitionOR portion is usually the most highly stressed part of the exhaust system, and having the highest point of stress coincident with a weld is often not recommended. Weld contamination and poor weld OF BE penetration are two factors that can lead to failure at this point. Mitigating stress Flanges are often cast or sometimes machined from solid. These methods allow the designer to mitigate the stress concentration in the TO area between the flange and the tube, and also to exercise control PRINTover the cross-sectional area; a smooth transition here can prevent unwanted flow separation at a sharp transition. Rapid prototyping methods that allow metallic parts to be produced directly are sometimes also used to produce small quantities of exhaust flanges. IN However, this practice is not common at the moment. NOT With pressure in racing to produce ever lighter components, the onus falls on the exhaust manufacturer to supply the methods to Inconel was once the preserve of Formula One and CART but is now achieve this. A tube with a 50 mm (2 in) diameter and a 0.5 mm used widely, although by no means universally, in NASCAR Cup (and (0.020 in) wall thickness is not an off-the-shelf item, and where an even by some Nationwide teams). It is also finding use outside these exhaust system warrants such material, the exhaust maker has to do top-endPROPERTY series, with some manufacturers using it in motorcycle sport one of three things – he can refuse the job, commit to taking a 150- to replace titanium. With good high-temperature properties in very 300 m (500-1000 ft) minimum order quantity from the mill on seven thin sections, Inconel compares well to titanium in terms of system or eight months’ lead time or, as is becoming increasingly common, mass, and lasts longer. Fig. 8 shows part of an Inconel exhaust system. make the material himself. Superalloy tubes generally need to be produced from sheet material, The investment in equipment to do this is considerable, but it

and for race exhausts some components are made from tubes less than allows exhaust makers to react very quickly to customer requests. t

40 HyTech Exhaust Inc Developing & manufacturing racing exhaust since 1984 Anti-reversion technology Stainless-Inconel-Titanium Custom bending & fabrication

HyTech introduces the Nozzle Merge Collector State of the art design using CFD technology Increased velocity & scavenging Available in 2, 3, 4, 5 into 1 designs

Patent # US20100146956A1 HyTech Exhaust Inc 12 Hammond Dr. Suite 203, Irvine, CA 92618 949-581-2181 [email protected] • www.hytechexhaust.com

Untitled-1 1 08/02/2011 21:26 Fig. 9 – This picture shows an Inconel 718 exhaust collector made by rapid prototyping. The method offers unique opportunities to make geometries impossible by conventional means

Moreover, they are less likely to the collector that make manufacture even more find themselves with an odd size complicated. of material in stock when the I’ve mentioned hydroforming in relation to forming customer decides after a short time sheets, but it has also been used successfully for many that they actually want to use a years for forming complex exhaust pipes, and used different size of material. widely for producing two-stroke expansion chambers. When the manufacturer has In this latter case, two sheets of the same shape are the tube he requires, and if the welded together along their edges and pressurised exhaust system is a simple tubular internally MEDIA.to form a shape with a round cross-section, affair, the tubes have to be bent to the correct radii. This is most often but varying in diameter as required and with a complex twisting done now using automated equipment, and our interviewees report centreline in one plane. that producing good-quality bends in the thin material now in vogue More recently, and more expensively, some manufacturers have is much more difficult; a slight reduction in wall thickness can make looked at hydroforming to produce complex tube shapes in order to things even more so. Another difficulty is the problem of ‘spring-back’ aid packaging. This process can produce precisely ‘squashed’ forms when forming bends, especially in stronger materials. This means repeatably where packaging constraints are very tight, by expanding that a greater bend angle must be specified than is actually required, a tube under hydraulic pressure into a mould tool. One manufacturer with the bend tube then springing back to the correct bend angle – states that hydroforming is the preferred manufacturing method for very hopefully! tight bends, with a centreline radius less than the diameter of the pipe. Where the exhaust port exit from the cylinder head is not round, Rapid prototyping has limitless possibilities. While the present it is likely that the first portion of the exhaust after the flange will not POWERstate of the technology makes metallic parts expensive and slow be round either. The complex transition from the ‘racetrack’ shape to to manufacture – although the first prototypes can be ready very a round shape is difficult to produce when the section is commonly quickly – this will improve, and it is likely that exhaust manufacture, expected to curve away in two planes. especially in prototype quantities, will be able to take advantage of this in the future. The materials available already include some suitable Bespoke tooling for race exhausts, andONLINE more than one manufacturer has looked at In this case, exhaust makers often produce these parts by pressing the possibility of making parts by this method, with others admitting sheet metal using a bespoke tool manufactured to produceHIGH a certain to using the technology on current systems. Fig. 9 shows an exhaust bend. A male tool may be used with a corresponding female tool, or REPUBLISHEDcollector made by rapid prototyping methods. the parts may be pressed into rubber. Single-sided hydroforming could One exhaustOR company which undertakes a lot of manufacturing also be an economical way to produce such forms if the quantities are and materials development uses investment casting for a surprisingly sufficient to warrant the investment in tooling. The pressed forms are wide range of applications, from exhaust flanges to collectors and then welded together before being used asOF part of the exhaustBE system. even tailpipes. Collectors, where a number of pipes are brought together, can often When the manufacturer has the requisite parts to make the system, be the most complex parts to manufacture. Owing to the small included he needs to weld these together and, as we might expect, the more angle at which the pipes are brought together, welding access is at exotic the material, so the weld method becomes more complex. best awkward in many cases. The subsequent lack of weld penetration Mild-steel exhausts can be welded by a number of methods, and most can lead to areas of considerable stress concentrationTO in the collector. reputable manufacturers will use an inert gas method. Mild steel is a Moreover, some people find advantage from detailed changes PRINTwithin forgiving material in that gaps can easily be bridged. Stainless is generally welded by TIG methods, and to achieve a good quality weld, the pipes are often back-purged (filled with an inert gas) so that there is IN an inert atmosphere on both sides of the weld pool NOT to prevent oxidation. The inert atmosphere on the welder’s side of the joint is provided by the inert gas supply to the welding equipment. These same stringent requirements also apply to titanium and Inconel systems. PROPERTY There are a number of circumstances in which we might choose to coat exhausts. Some people choose to coat their systems to prevent corrosion, and there is a buoyant market catering to those who prefer A titanium rapid prototype exhaust flange a coloured exhaust system on the type of roadcars (Courtesy of Chris Tullett Exhausts) that also often masquerade as mobile audio systems.

42 FOCUS : EXHAUST SYSTEMS

The role of CFD in exhaust development is relatively limited at the moment, being the preserve of well-funded teams, but it can be used to check for the presence of flow separation and to optimise the pipes in terms of pressure losses along them. Using bends that are too sharp can lead to excessive pressure losses in the exhaust system, which manifest themselves as high exhaust back-pressures, and this can causeMEDIA. loss of performance. Where finding every last horsepower is critical, and where packaging doesn’t allow the use of generous bend radii, CFD can be used to identify problem areas and solve any problems before committing to exhaust manufacture. For a more in-depth look at the role of CFD in race engine design and development, this issue of RET also features a focus on CFD. Fig. 10 – This graph illustrates the effectiveness of thermal barrier coatings in reducing manifold surface temperatures (Courtesy of Zircotec) There is at present a move among car producers toward smaller, lighter and more efficient engines. For gasoline Happily, however, the most common reason to coat exhausts in racing engines, an important part of this strategy is the adoption of is to do with engineering rather than cosmetics. POWERturbocharging. Thermal barrier coatings are commonly used to minimise the effect of Motorsport, more conscious than ever of its environmental radiated heat within the engine bay, which can have a serious effect on ‘responsibilities’, has started to adopt turbocharged engines. The IndyCar reliability. Fig. 10 shows some experimental results of manifold surface series has decided to use them from 2012, and Formula One will follow temperature with and without a thermal barrier coating. In the case of suit from 2013. The ACO Le Mans regulations – upon which the rules for turbocharged engines, the retention of heat within the exhaust gases ALMS, LMES and so onONLINE are based – already allow turbocharged engines, improves the operation of the turbocharger. and companies such as Mazda now compete using them. The Mazda As mentioned earlier, there are various ways in whichHIGH the exhaust engine is a four-cylinder, 2 litre unit. Rumours are rife at the time of mass flow can influence the performance of a vehicle. As stated, REPUBLISHEDgoing to press that the factory LM P1 cars for 2011 will also early aircraft pioneers soon learned the value of ducting the exhaust be 2 litre ORturbocharged units. backwards to provide extra thrust. This places special demands on the exhaust system. When you see a turbocharged race engine on the dyno on full throttle, the exhaust Ducting the flow OF BE headers glow bright red. Formula One and IndyCar will both place At high road (or air/water) speed, ducting the exhaust to a low-pressure particularly high demands on any exhaust system, given the percentage area at the rear of the vehicle can help with scavenging, lowering of the lap that is spent at full throttle. In order to achieve low-mass the exhaust exit pressure. By ducting the mass flow toward a wing exhaust systems it is inevitable that superalloys will need to be adopted. (which needs to be properly protected), we can influence downforce, A further significant change compared to a naturally aspirated exhaust as we can if the exhaust exit is within the diffuser.TO The example of the is the additional mass of the turbocharger assembly that needs to be Norton exhaust could be followed on a modern single-seater, PRINTwith supported. These assemblies, while well-engineered, are considerable sidepods forming a radiator duct. If the exhaust flow was ducted into masses and, combined with the shocks and vibration due to service t the sidepod downstream of the radiator, it should induce more flow through the duct under high engine mass flow rate conditions. This Cosworth 3.0 litre V10 Formula One offers the possibility of reducing radiator sizes. IN exhaust exquisitely crafted in Inconel (Courtesy of Primary Designs/ Where exhausts are concerned,NOT simulation generally comes in one Ian Rycroft Photography) of two categories – 1D cycle simulation or 3D computational fluid dynamics (CFD). 1D cycle simulation can be used to quickly identify the best pipe lengths and diameters to be used and determine the optimal exhaustPROPERTY configuration, and can be used at the engine design stage. However, it remains a useful development tool on existing engines, where alternative configurations can be ‘tested’ to give a direction for developing physical parts. While the software is quite specialised, it can save a great deal of time and money, and can also improve the speed of development.

43 FOCUS : EXHAUST SYSTEMS

Moto2, the new class of four-stroke motorcycle Grand Prix loads, the challenge for exhaust road racing, has been a hotbed of exhaust development. designers and suppliers will be to Compare the link-pipes on the system in Fig. 7 to this system (Courtesy of Arrow Special Parts) maintain reliability. Turbocharger assemblies are commonly supported by brackets or tie-rods, to prevent the extra mass being cantilevered off the cylinder head. In general, the turbocharger will have a wastegate, a device that limits boost pressure by allowing a proportion of the exhaust gas to circumvent the turbine as the boost pressure limit is reached. MEDIA. The wastegate exit pipe generally joins the tailpipe a short way downstream of the turbine. At many tracks in the US it is now mandatory to run with a muffler/ silencer. Perversely, it has been reported that it is permitted to run with character of the torque curve, and some manufacturers have chambers something that looks like a muffler but which has no noise attenuation connected to the main exhaust pipe specifically for this purpose. qualities whatsoever, besides its volume. In Europe, there is rarely With the drive for low system mass, failures are inevitable, and this any requirement for a muffler, but there is always (apart from special will drive developments which aid reliability. One manufacturer spoke events) a requirement to come within a strictly policed decibel limit, of developing elements that will damp high-frequency vibration and which is part of the scrutineering/technical inspection. Those falling improve fatigue life. foul of the man with the noise meter are instructed either to remedy The move among regulators towards turbocharged engines in racing the problem or, failing this, to go home. POWERis likely to lead to considerable changes in exhaust design. Where regulations remain fixed on naturally aspirated engines, as they will Noise attenuation in many series, exhaust development is likely to proceed at a slower With many race tracks under pressure from local authorities because pace. However, in such cases, NASCAR being an example, exhaust of noise levels, these rules are taken seriously. A lot of work goes into manufacturers are offering the teams an advantage in longevity or designing silencers that are effective in terms of noise attenuation but mass reduction by usingONLINE more advanced materials. which do not cause excessive back-pressure in the exhaust system. Continuing development of materials and manufacturing mean the Exhaust companies are also keen to find new packingHIGH materials for suppliers will have much to offer in years to come, and the pace of car noise attenuation in the muffler/silencer. Popular materials used in the REPUBLISHEDdevelopment and the of new regulations means race teams will construction of mufflers are carbon fibre, titanium and aluminium, or keep the ORsuppliers busy for a long time into the future. mixtures of these. One interesting effect of turbocharging is that such engines References generally require less noise attenuation, asOF the turbine removesBE a 1. Morse, P.M., Boden, R.H. and Schecter, H., “Acoustic Vibrations proportion of the energy from the exhaust flow. and Internal Combustion Engine Performance, Journal of Applied The advent of the diesel race engine in motorsport has brought with it Physics”, Vol 9, 1938 the diesel particulate filter (DPF). The ACO Le Mans rules mandate that 2. Hooker, S., Read, H. and Yarker, A., “Performance of a there is no visible smoke, so the diesels are notably both clean and very Supercharged Aero Engine”, 1941 (reprinted 1997, Rolls-Royce quiet. The DPF works by trapping soot and hydrocarbonsTO on the surface Heritage Trust, ISBN 1-8729-2211-2) of the filter until such time as conditions (excess oxygen and highPRINT 3. Pinkel, B. and Voss, F., “Experimental Determination of Exhaust Gas enough temperatures) allow for the combustion of these particles. Thrust”, NACA Special Report 139, 1940 The nature of motorsport – as with any form of sport – is to look for 4. Vorum, P.C., “Short Pipe Manifold Design for Four-Stroke Engines”, competitive advantages, and exhaust systems can be used effectively ASME Paper here. The ‘blown diffuser’ in Formula One was seen toIN be an 5. Smith, P., “Scientific Design of Exhaust and Intake Systems”, advantage when it was discoveredNOT that some teams were using it, after , ISBN 0-8376-0309-9 t which other teams felt it necessary to adopt the same strategy. In changing the diameters and lengths of various parts of the Acknowledgements system, it is possible to alter the shape of the torque curve, which can The author would like to thank the following for their help with this help with the driveability of the car. While electronics can be relied article: Steve Sousley of ProFabrication, Joe Ellis of BTB Exhausts, onPROPERTY to remove any excess torque, or where its rate of change is too Martin Hagele of MHG Fahrzeugtechnik, Neil Morgan of Good Fabrication, Jack Burns and Vince Roman of Burns Stainless, Pat rapid, it can be a better strategy to change the character of the torque Barrett of Primary Designs, Stuart Barron of SS Tube Technology, curve by changing the configuration of the exhaust. Linking different Primoz Jurman of Akrapovic, Chris and Andy Tullett of Chris Tullett headers with smaller diameter pipes is common in motorcycle racing, Exhausts, Rafaele Rosi of Arrow Special Parts SpA and where a number of manufacturers supply systems of this type. Even Ryan Raymond of Yoshimura R&D of America. in single-cylinder four-stroke classes, efforts are made to change the

44 Untitled-1 1 08/02/2011 21:28 FOCUS : EXHAUST SYSTEMS

SOME EXAMPLES OF EXHAUST SUPPLIERS

ARGENTINA Quicksilver Exhausts Conforma SRL +44 1428 687722 www.quicksilverexhausts.com +54 3462 429604 www.conformainox.com.ar RS Fabrication +44 1295 266655 www.rsfabrications.com AUSTRIA Scorpion Exhausts Remus Innovation +44 1773 513730 www.scorpion-exhausts.com +43 3142 690000 www.remus.at Simpson Race ExhaustsMEDIA. +44 1753 532222 www.simpsonraceexhausts.com FRANCE SS Tube Technology DEVIL S.A.S. +44 1865 731 018 www.sstubetechnology.com +33 4 75 84 74 90 www.devil-exhaust.com Titanium Performance UK +44 845 094 8884 www.titaniumperformance.co.uk GERMANY Torque Technique HJS Fahrzeugtechnik GmbH +44 1722 744 747 www.torquetechnique.co.uk +49 2373 9870 www.hjs.com Vortex Exhaust Technology MHG Fahrzeugtechnik GmbH +44 1708 861078 www.vortex-performance-exhausts.co.uk +49 71739 27330 www.mhg-fahrzeugtechnik.de Proto Technik USA +49 7171 8748 100 www.prototechnik.de Bassani Xhaust POWER+1 714 630 1821 www.bassani.com ITALY Borla Arrow Special Parts S.p.A. +1 805 986 8600 www.borla.com +39 075 861811 www.arrow.it Brocks Performance Products Lesto Racing +1 937 912 0054 www.brocksperformance.com +39 389 423 4258 www.lestoracing.com Burns Stainless ONLINE Termignoni +1 949 631 5120 www.burnsstainless.com +39 01317 1666 www.termignoni.it Coast Fabrication +1 714 842 2603 www.coastfab.com SLOVENIA HIGHREPUBLISHED Dynatech Akrapovic +1 812 897 3600 www.DynatechHeaders.com +386 17878404 www.akrapovic.si FlowmasterOR +1 707 544 4761 www.flowmastermufflers.com UK Heartthrob Exhaust, Inc Alunox Exhaust OF BE +1 320 693 0222 www.heartthrobexhaust.com +44 1978 851100 www.alunox.co.uk Hedman Hedders Ashley Competition Exhausts +1 562 921 0404 www.hedman.com +44 1922 720767 www.ashleycompetitionexhausts.com HyTech Exhaust BTB Exhausts +1 949 581 2181 www.hytechexhaust.com +44 1327 261 797 www.btbexhausts.co.uk Kooks Custom Headers Chris Tullett Exhausts Ltd TO +1 866 586 5665 www.kookscustomheaders.com +44 1296 483777 www.christullettexhausts.com PRINTMagnaFlow Performance Exhaust Double S Exhausts +1 800 824 8664 www.magnaflow.com +44 1884 33454 www.stainlesssteelexhausts.com ProFabrication Inc Good Fabrication +1 704 795 7563 www.profabrication.com +44 1844 202 850 www.goodfabs.com IN Pypes Performance Exhaust Janspeed +1 215 712 9982 www.pypesexhaust.com +44 1722 321833 www.janspeed.comNOT Reid Washbon Racing Exhausts Jetex Exhausts +1 949 548 9783 www.reidwashbonracing.com +44 1789 298989 www.jetex.co.uk SuperTrapp Industries, Inc. JP Exhausts +1 216 265 8400 www.supertrapp.com +44 1625 619916 www.jpexhausts.co.uk Yoshimura R&D of America PROPERTYMilltek Exhausts +1 909 628 4722 www.yoshimura-rd.com +44 1332 227 280 www.millteksport.com Vance and Hines (USA) OJZ Engineering +1 562 921 7461 www.vanceandhines.com +44 1777 248844 www.ojzengineering.co.uk Primary Designs +44 1844 216057 www.primarydesigns.co.uk n

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