Chassis: Pressed Steel (BMW)
Class: GTE
Engine: BMW P65 3999cc V8
Fuel: Petrol
Transmission: Xtrac 6 speed
Brakes: steel
Weight: –
Fuel Tank: –
Year introduced: 2009
BMW’s fourth generation M3 racecar, based on its E92 production car, made its competition debut in the 2009 Sebring 12 Hours. The two GT2 cars entered by Rahal Letterman Racing failed to finish the race, although one of them had run second in class for almost half of the race. Later in the year, the M3s finished first and second in the GT2 class in the American Le Mans Series round at Elkhart Lake and, by the end of the season, picked up GT2 podium finishes at seven of the 10 rounds of the ALMS.
The BMW M3 GT2 racecars are built using pressed steel bodyshells taken from the M3 production line at Regensburg, which has been used for production of sporting versions of the manufacturer’s road car models since the first iteration of the M3 in 1986. Installation of the CAD drawn and FEA tested BMW Motorsport rollcage / chassis frame is carried out by a subcontractor, which also modifies the floorpan to accommodate a transaxle rear end and a racing exhaust system. The wheelarches are enlarged to allow the potential for the front and rear track to be extended to the full 2000mm width allowed under the ACO GT2 rules.
A dry sumped racing version of the BMW P65, all aluminium, 90-degree V8 engine powers the M3 racecars. This has the same bore and stroke dimensions of 92mm and 75.2mm as the production power unit giving a swept volume of 3999cc. In its initial ALMS competition form, with two 30.1mm air inlet restrictors fitted, the engine generated 460bhp at 7500rpm with maximum torque of 500Nm at 5500rpm. For the engine’s 2010 configuration, BMW Motorsport quotes a peak power output of 500bhp at 8750rpm. In contrast, the production engine develops 420bhp at 8300rpm with a peak torque output of 400Nm at 3900rpm.
Castings for the P65 engines are produced at BMW’s light alloy foundry in Landshut, the same facility at which its Formula 1 engine castings were produced. The aluminium alloy cylinder block incorporates a bed plate lower section, which carries the five main bearings that support a forged steel crankshaft driven by steel connecting rods and fully skirted forged aluminium pistons. Power for the aluminium alloy, double overhead camshaft cylinder heads is taken from the nose of the crankshaft and is transmitted to the four valves per cylinder via rocker arms and steel bucket tappets.
The P65 engine management systems is based on BMW Motorsport’s type 408 ECU, which comprises two high performance microprocessors that control the multipoint fuel injection system. Ignition is via a single, centrally-mounted spark plug in the roof of each combustion chamber, fired by its own dedicated coil. A lambda controller, pit lane speed limiter and the engine data memory system are also controlled by the ECU.
In the M3 production car, the gearbox is located immediately behind the engine, while in the GT2 racecar it has been re-located to form part of the rear axle assembly. As a result, the engine location in the racecar is lower and further rearward than in the production car, to the benefit of weight distribution, handling and traction. Xtrac supplies the six speed, sequential shift transaxle gearbox, which is equipped with straight cut, unsynchronised gears. The ‘Quick Shift’ actuation of the gearbox is also controlled by the ECU, which provides an ignition cut during gear changes.
Power from the engine is transmitted to the gearbox via a steel propshaft and a three plate, 7.25in diameter carbon clutch mounted on the front of the gearbox. A mechanical limited slip differential and a traction control system apportions drive to the rear wheels.
Further rearward weight bias is achieved by the positioning of the driver in what is effectively the rear seat area of the production car.
The M3’s front and rear suspension systems comprise fabricated steel uprights, configured to offer enhanced castor and camber angles, and connected to the chassis by double wishbones with five-way adjustable dampers and concentric springs mounted between them. Body roll is controlled by non-driver adjustable tubular steel roll bars, which are attached directly to the wishbones. A 20mm tolerance is permitted on suspension pick up locations relative to the production car.
The M3 racecars are stopped with 380mm ventilated grey cast iron front brake discs and six piston AP Racing calipers. At the rear, the 355mm rear discs are gripped by four-piston calipers.
The competition M3s are equipped with a BMW Motorsport safety seat system and a removable carbon roof panel. In the event of an accident, an injured driver can be lifted out of the car through the roof while still strapped into the seat.
Aside from the roof panel, the front and rear valances, the bonnet and boot lids, the side rocker panels, the front wings and rear wheelarches are also all carbon fibre mouldings with Kevlar reinforcement where necessary.
As with any front-engined racecar, driver cooling is an important consideration in the M3 due to the need to route the exhaust system under the cockpit floor. ACO rules require all closed top cars to be fitted with an air conditioning system that maintains a cockpit temperature of no more than 32degC and BMW Motorsport claims its system works well enough that no additional driver cooling measures are necessary. In order to maintain its efficiency, the volume of the driving compartment is reduced by the fitting of a plastic divider screen behind the driver’s seat. This, perhaps more than anything else, epitomises BMW’s ‘Efficient Dynamics’ philosophy, in which parts and systems are maximised for optimum performance and efficiency. The air conditioning system works ‘on demand’, so when the desired temperature is reached, the system disengages to reduce parasitic losses. Likewise, the M3’s power steering system, which is ‘corner sensing’, only supplying assistance when required and disengaging when the car is straight.
The BMW P65 engine, which was derived from this unit and powers the BMW M3 GT, has been further improved within the regulations. The eight individual throttle valves receive their intake air via a system made of carbon fibre with loadcharge optimised ram tubes. The mechanics have been adjusted to meet the extreme demands of GT and endurance racing: as a result, the BMW P65 has a steel crankshaft, forged skirt pistons, high-performance steel conrods and a dry sump lubrication system.
This allows the engine to achieve 500bhp. Due to this the BMW M3 GT is able to perform the sprint from 0 to 100km/h in 3.42 seconds. With 500cc per cylinder and the stroke to bore ratio of 72.5 x 92 millimetres, the engine fulfils the ideal conception of demanding engine designers. The cylinder block is designed with a bed plate lower section and made of a special aluminium alloy. The unit’s dimensions, capacities, number of components and extremely light weight make it the perfect engine to use on the race track.
Intelligent control systems are at work in the BMW M3 GT. Via two bus systems, the PO WER400 control unit actuates all the accessories fitted to the car, such as lights, wipers, etc. Traditional relays and fuses are thus eliminated, ensuring considerable weight saving, improved reliability and ease of application. The functions of the BMW P65 engine are managed by an ECU408 electronic control unit, developed in-house by BMW Motorsport. This unit uses two high performance micro-processors to control the individual cylinder injection and ignition, as well as the engine data memory system, among other things.
The ECU408 monitors the “Quick Shift” function of the six-speed sequential gearbox on the BMW M3 GT, which suppresses the ignition when changing gear, thus allowing even faster gear changes. The compact transmission unit is positioned on the rear axle to allow optimal weight distribution. The drivers are assisted by a mechanical limited slip differential and traction control.
The engineers have not only modified the power train for use in races, but also the chassis. The front and rear axles on the BMW M3 GT have an increased wheel castor angle, enlarged track width and greater wheel camber than the series version. The shock absorbers can be adjusted five ways and tubular stabiliser bars can be used to set up the car for a specific track.
The use of high-tech carbon fibre reinforced plastics (CFRP) played a crucial role in the car achieving a weight of 1,245 kilograms (in ACO specification).
As well as the roof of the BMW M3 GT, the front and rear aprons, bonnet, boot lid, rocker panel, doors, front wing, rear wing and flared rear wheel arches are also made of carbon fibre.
The aerodynamics of the BMW M3 GT were fine-tuned for the 2011 season using computational fluid dynamics (CFD) and the BMW Group‘s modern wind tunnels. The result is a new aerodynamics package with even greater efficiency than last year‘s version.
When developing the BMW M3 GT, it was also possible to use computers to optimise the geometry and kinematics of the chassis and determine the most efficient locations for attachment points on the axles. At the same time, elaborate calculation programmes also made it possible to simulate distortion of the chassis under extreme strain.
Using extensive investigations in the wind tunnel, the engineers were able to verify the results of the CFD calculations before starting to build particular components. Maximum reliability and precision during these wind tunnel tests could be applied.
High-performance compound brakes ensure excellent deceleration in the BMW M3 Coupé, the brakes in the BMW M3 GT have a fixed-calliper design.
The aluminium brake callipers consist of six pistons on the front wheels and four pistons on the rear wheels. The inner-vented grey-cast iron brake discs on the BMW M3 GT2 have a diameter of 378mm at the front and 355mm at the rear.
As a development partner of BMW Motorsport, Dunlop equips the BMW M3 GT with high-performance racing tyres, which optimally transfer the acceleration and braking torque to the track and are able to withstand extreme lateral forces. The tyre manufacturer has been involved in the development of the GT sports car right from the word go. The BMW M3 GT takes to the track on 18-inch wheels with magnesium rims.
Updates
BMW has fitted a very distinctive set of BBS rims to its pair of GTE entries, it has also sprouted two small dive planes behind the rear wheel arches.
