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Touring Car exhausts

Somehow the name ‘Touring Car’ doesn’t seem to fit well with the on-track action. These machines are hardly the beautiful coupes of yesteryear, with a luggage rack and which were actually designed for touring. Touring car racing is now hugely popular, from the fire-breathing DTM cars to the slightly more docile but no less exciting WTCC and BTCC entries that continue to attract top drivers and manufacturer backing.

These are, after all, road-going cars – you are meant to be so impressed that you rush out to buy one – but it would be wrong to assume that these are simply stripped-out shopping cars; studying their exhausts alone makes that obvious.

It is highly unlikely that a passenger car exhaust would last a full season or more of racing at WTCC level. However the bespoke racing systems that replace them are expected to achieve this target. Replacing exhausts on a regular basis owing to fatigue is not top of the list, especially when race weekends are often taken up with repairing more obvious external damage!

Some parts will need to be changed due to damage sustained during racing, but the systems are designed to isolate damage, thus protecting the rest of the system. For cars with rear-exit systems, it was common to wreck or at least damage almost every part of them if the car was hit from behind. The whole crash load was transferred through every component in the exhaust line, and much of the load was reacted by the primaries, requiring a very expensive exhaust system and much time-consuming work on the car.

Exhaust systems have been developed which incorporate a collapsible section, similar in principle to a passenger car’s crumple zone or to the tubes used to retard a vehicle in a crash test. This dissipates most of the energy involved and therefore isolates the expensive forward components from damage. Another cause of impact damage can be heavy use of the kerbs; this can damage exhausts on some cars where the exhaust routing leaves them exposed.

BTCC cars have to conform to strict exhaust noise regulations. Despite having to use a turbocharger (which attenuates exhaust noise) and a catalyst, which again removes some energy, a silencer is also required. These are packed with a noise-insulating material which, over time, loses its effectiveness as it becomes contaminated and compressed. The silencer is designed to be serviced though, during which the exhaust packing is renewed.

The use of a catalytic convertor in BTCC is mandated, and to prevent anyone turning this to their advantage an homologated catalyst has to be used.

Exhaust heat needs to be managed carefully. If you look at the Dynojet Toyota BTCC car [Fig. 1], you’ll see that the primary pipes have a thermal barrier coating. Retaining heat in the exhaust helps transient engine response under acceleration. Not only is heat management for performance a concern, it is also a consideration for driver comfort. The exhaust systems of touring cars are often coated or wrapped with insulating materials in order to limit the heat transfer to the driver compartment – this is discussed in more detail in this month’s article on coatings.

Despite the very competitive nature of touring car racing, the materials used for exhaust manufacture aren’t the most expensive available – austenitic stainless steels are still used in preference to more exotic choices such as Inconel or titanium.

Fig. 1 - The BTCC Dynojet Toyota uses thermal barrier coatings on its exhaust primaries (Courtesy of Dynojet Racing)

Written by Wayne Ward

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