Building a BMW 320si WTCC

When the BMW 320si WTCC made its debut in the FIA World Touring Car Championship on 2nd April 2006, the impressive race car immediately showed evidence of its capabilities: Andy Priaulx not only took pole position in Monza, but also drove the car to victory in the first race. Ten further triumphs followed during the season. The drivers from the BMW national teams won nine times in 2007 and six times in 2008.

The 320si WTCC raced in the FIA World Touring Car Championship is packed with modified parts - the staples of the high-tech motorsport industry.
That certainly does not mean though, that the racer is unrelated in any way to its sister on the road - far from it, and the virtues of the original are reflected and magnified in the racer.
To simplify matters (and they do need to be), the FIA book of technical regulations for the cars is long and complicated. The car can be examined in three parts - bodyshell, suspension and engine/drivetrain.

The bodyshell is broadly standard. It has an aero kit designed to strict series rules, which is fixed for the season, and extensive safety provisions, such as the rollcage and some added impact-absorbing material.

The engine block and cylinder head are original parts, but the majority of the other engine parts are specially created components. The rules restrict items such as flywheels weight, valve lift and compression ratio. The engines produce around 275bhp (more than 100bhp more that the road car).

The gearbox casing for the five-speed H-pattern gearbox used by BMW is standard, but the internals are modified and the ratios are different - though they are fixed for the season. Similarly, the differential casing is an original part, but the internals are race parts and the diff' ratio can be changed to suit different circuits.

The clutch is a special carbon-fibre unit. While the rules give free rein on the propshaft and driveshafts, they must be made from steel.

Springs and shock absorbers are proper racing parts, but crucially for a manufacturer such as BMW with a strong base car, the suspension must follow the same design as that on the road car and the mounting points can only be moved a small distance - in some instances 20mm, in others 10mm.

Brakes are to racing specification, but the rules restrict the size of discs, their material (steel) and the number of pistons per calliper (four at the front, two at the rear). Again they are homologated parts and are fixed for the season.

Steering must broadly come from a production car, but not necessarily the base vehicle - for example when Andy Priaulx, Jorg Muller and Augusto Farfus turn their steering wheels in anger they are assisted by a pump from the MINI.

It's necessarily a complicated and subtle business making a superb race car from a superb road car, but Priaulx's team boss Bart Mampaey cuts to the chase when he points out "The road car has a wide track (which is ideal for racing), perfect weight distribution, and the suspension kinetics are very good indeed."

For 2009, many areas of the vehicle were enhanced. The spring/damper system was significantly improved as well as the ECU404 engine control unit, which had been developed by BMW Motorsport. It now makes for a better driveability of the gearbox and makes shifting easier. In addition, the new chassis components for the BMW 320si WTCC facelift, which will be used from Marrakech onwards, were integrated into the concept of the car.