BMW Rahal Letterman M3 GT2 Briefly Dissected

With the grueling 1000 mile (or 10 hours) Petit Le Mans endurance race just hours away we thought we’d try and explain some of what makes these cars so special. Sure the ///M3 in its fourth generation is already a high performance machine from the factory but steps are necessary to make it the best it can be on the track while complying with the sanctioning body rules.

The heart of all cars is the engine, and it is fair to say that BMW Motorsport has built one that really ticks. The P65, as it is known internally, is based on the S65 production motor with some serious upgrades. The displacement of 4.0 liters has been unchanged (72.5 x 92 millimetres with 500 ccm per cylinder), but the crank is upgraded to a dual plane steel version and the pistons have forged skirts to keep up with rigors of racing at the highest levels. A dry sump oil system is employed to keep all the friction at bay, with the aluminum storage tank mounted to the rear of the engine (where the transmission is normally). This high revving V8 breathes through eight individual throttle bodies being fed by a carbon fiber airbox. With all of that and some more tricks the P65 produces over 500 horsepower and hits 60 in 3.4 seconds.

When moving that quickly, braking must never be overlooked and the GT2 excels at that as well. Featuring high-performance AP Racing compound brakes with 6 piston aluminum calipers up front and four pistons out back. The inner-vented grey-cast iron brake discs on have a diameter of 378 mm at the front and 355 mm at the rear, worth noting is that they are slotted and not drilled and this is to prevent warping and spidering.

The power is transferred to the wheels via an Xtrac six-speed sequential gearbox placed in the rear of the car to improve weight distribution. Through extensive use of electronics and computer processing BMW has devised a way to make shifts quicker and less stressful on the driver and car drivetrain- the electronic control unit is able to cut ignition briefly (this has made its way to production models in the X6/X5 ///M). Like street cars, these M3s feature a mechanical limited slip differential and a traction control system that began as part of BMWs F1 effort.

The chassis and bodywork have received numerous changes. Body panels are made of Carbon Fiber to decrease weight and the aerodynamics have been thoroughly tested in the wind tunnel to create both down force and to limit drag. The front and rear axles have increased wheel castor angles and increased track compared to the serial versions. The shock absorbers can be valved and stabilizer bars can be tuned individually to set up the car for a specific track or driver combination

In tomorrow’s heat the drivers will get a breathe of cool air from the mandatory air conditioning system which runs only when it will not impact the engine output.

Dunlop has created an all-new tire for this endurance race in conjuntion with BMW Motorsport. These cars feature Volks racing wheels in aluminum, and they are made in Japan even though the name is German!

Other adjustments made for Petit Le Mans include: a new quick-change front bumper and improved headlights.

Stay tuned to for more BMW RLR Racing coverage from Petit Le Mans

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