Touring car exhausts
The British Touring Car Championship (BTCC) is renowned for being a keenly contested and competitive series. It has remained popular for decades and continues to attract a strong field of domestic and international drivers. Team Hard will contest the BTCC in 2013 using two Vauxhall Insignia VXRRs. Thorney Motorsport has supplied the cars and developed its own exhaust system to suit the installation of the race series' spec engine, after its exhaust supplier failed to produce a sufficiently reliable system.
In the BTCC, competitors have the option of tuning their own engine, sourcing one through an engine supplier, or running the series' spec engine, which has proven to be a competitive option. The spec engine is a four-cylinder turbocharged unitand the exhaust manifold is part of the engine as supplied to the teams. In developing its own exhaust, Thorney had to design and manufacture the link between the exhaust manifold and the turbocharger, plus all the pipework beyond the turbine.
The manifold supplied with the engine is a ceramic-coated component. As has been discussed in Race Engine Technology magazine and various coatings articles for RET-Monitor , ceramic coatings provide a useful thermal barrier, protecting components that are in to the engine, preventing excessive heat radiation back into the engine and cooling fluids, and keeping the heat in the exhaust gas flow, improving turbocharger transient response.
Thorney Motorsport's John Thorne says the exhaust system was designed with various goals in mind. Low mass was stated as being an important aim, as was ensuring sufficient performance in terms of maximum power but also peak and mid-range torque. Reliability and impact resistance were also mentioned.
It is widely held that superalloy materials such as Inconel provide the lightest exhaust; this has been shown to be true through its use at the highest levels of motorsport. However, it does require some very specialised welding techniques, such as welding in an inert atmosphere, with the pipes also purged with an inert gas, so they do not lend themselves to trackside repairs. So an austenitic stainless steel (type 304) is specified, with on-site welding being an important consideration. The longevity of the system, if there is no impact damage, is expected to be at least one racing season. The teams do not expect to have to carry lots of exhaust spares, and so trackside repairs in the event of an unexpected impact have to be considered.
There are other considerations in the design of the exhaust system. The mandated single side exit and the series-spec sills mean the exhaust system has to pass through the sills. Careful design and installation ensures that the exhaust system does not make contact with the inside of the glass-fibre composites sills, as this can easily cause a fire.
Thorney has designed a clever system with some compliant elements that allow the car to suffer side impacts without permanent damage to the exhaust supports. While other teams are often sidelined through exhaust system failure following an impact, the Thorney-supplied cars have benefited from some creative thinking and are relatively immune from such problems.
Written by Wayne Ward