The differing demands of touring car exhausts

Tuesday, September 30, 2014

Tags :  exhausts

While single-seater racing hogs most of the limelight in Europe, at least as far as TV time is concerned, there are some very popular national racing series based on touring cars that are a real hit with fans of live motorsport. The World Touring Car Championship (WTCC) is starting to attain the same level of popularity, and deservedly so – the quality of the entries in terms of the machinery and drivers is very high.

Many of the national championships and the World Touring Car series are based on cars that are available with a 2.0 litre turbocharged engine. As this is a popular choice for buyers of family cars in Europe, this is a sensible choice. In Australia, for example, their ‘touring car’ is a 5.0 litre naturally aspirated V8, while in Germany, the national motor manufacturers fight it out among themselves with 4.0 litre naturally aspirated V8 engines. In Japan, there have also been cars with V8s, some of which were bespoke V8 race engines based on endurance engines competing at Le Mans. The Vemac from the early 2000s, for example, used a Zytek V8.

The different race series have had very differing demands in terms of exhausts, not only in terms of layout but also such aspects as the physical size and operating temperatures. The turbocharged engines which are used in WTCC and Japanese SuperGT, for example, will run higher exhaust gas temperatures, for example, than those in naturally aspirated engines.

Even where engine regulations are superficially similar, there may be large disparities in engine output and therefore large differences in the effect on exhaust systems. Many touring car series are powered by engines that are limited in terms of power by intake air restrictors or fuel flow meters. Both devices have the same effect – they limit power by limiting engine speed. The Japanese SuperGT championship, which uses a fuel-flow limit, has 2.0 litre turbocharged engines producing around 500 bhp, while the WTCC has an air intake restrictor applied to the same type of engine, but with the resulting power output thought to be around 350 bhp.

The difference in maximum exhaust gas mass flow is proportional to the power output, so there may be noticeable differences in exhaust design in order to maintain performance. In particular, packaging the exhaust so as to avoid flow loss through flow separation from the ‘inside’ of bends in pipes might require different pipe bend centreline radii to be used. Apart from this difference, it wouldn’t be a surprise to find that different primary pipe diameters are used. To improve transient engine response, it is likely that any series using turbocharged engines will probably see teams running some form of thermal insulation on the primary pipes, which may be anything from a ceramic coating to a formed metal enclosure.

Such thermal insulation around the exhaust primary pipes is not necessary for naturally aspirated engines, although some form of exhaust insulation might be required in order to reduce heat transfer to adjacent components or to the driver compartment.

Written by Wayne Ward

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