Engine
The starting engine of the road going M6 uses a 560BHP M-powered twin turbo V8 petrol engine, “which hasn't needed much treatment to make it legible for GT racing” adds Marquardt. It’s based on the 4.4L road engine, which sees the same engine block and heads, with minor changes to the crankshaft and connection rods.
When the car was at pre-season testing, it had a power output of 640BHP, which meant it could keep up with the odd LMP2 or Daytona Prototype car over the course of a lap at the Daytona raceway. But balance of performance (BoP) soon had its say in that.
BMW have incorporated its very own variable valve timing system, as well as using its very own ‘VANOS’ and
VALVETRONIC’ for better performance. They are also using an updated direct injection system too, which is a lot different to the standard M6 one’s.
The ‘VALVE TRONIC’ system has an additional set of rocker arms between the cam lobes and valves. Their arms are controlled by a pivot motion as well as an electronically actuated shaft. These apply or reduce motion of the rockers itself. For
the ‘VANOS’ it works by rotating the drive sprocket at the end of the cam shaft to apply different timing. Between the two, they provide variable lift and timing on both the intake-exhaust valve on each side of the V8 block.
The engine's architecture is mounted very low and ahead of the front axle which gives the car a lower center of mass, which is better for cornering. Lots of weight up high will affect turn in, and present the driver with understeer. BMW have by far beaten their rivals here with the lowest mounted engine of the field.
The ‘V’ of the engine houses the twin turbos, which are clear to see. The wastegate and inlet manifold are also mounted on the top of the engine. The engine uses a very low air to air cooler which differs to the road going M6 which has a water to air cooler, but this is banned my regulation, “so an air to air is the best option here” claims Marquardt.
The exhaust and its manifold resemble the normal M6, which comes up and over the engine block, just ahead of the cockpit bulkhead. This is BMW’s ‘cross engine exhaust manifold’ which has been slightly changed for GT racing, where its longer, coated in a thermal barrier and its positioning, which is just ahead of the sills of the chassis.
In more detail the ‘cross engine exhaust manifold’ works by using two inlets on each twin scroll turbocharger is fed from two cylinders: one for the left bank of the engine, and one for the right. As a result of the concept, BMW is creating an exhaust pulse every 180° of crank rotation, something which BMW boss Marquardt is very proud off.
Cooling
The GT spec M6 sees a radical change in cooling design. For the engine cooling sees the traditional BMW grille used to provide the turbocharger with air, with the main duct in the front bodywork used for engine cooling. The ducts sit very low, for a better center of gravity. The ducts then split into two, to feed each bank of the engine flow for combustion. The air also passes a heat exchanger, which pumps cold air around the engine block. The front ducts are also used for brake cooling too.
All over the car sees small ducts to help cool components of the car. The central ducts on the car are used for driver cooling, as well as cool the exhaust manifold, whereby the system blows air onto the hot pipes.
Towards the rear, BMW has mounted a duct on the rear fender which is used for transmission and AC cooling at the back of the car. For rear brake cooling, they have also mounted a small duct ahead of the rear wheel, which is connected to the brake rotor via a plastic tube.
Running gear.
The transmission features a 7-speed box, which is mounted in a longitudinal manor. A great advantage here is the sequential, electronic gearbox, with many of its classmates have a mechanical one.
Suspension saw a lot R&D over the M6’s development cycle. Marquardt says: “It’s now utilizing a very efficient system” from all of the testing that was carried out. The design sees double wishbones all round with an anti-role bar at the front as well as at the rear, with some unique four-way adjustable dampers and shock absorbers.
The brakes are mighty on the M6, which is well ahead of its class rivals of Ferrari and Corvette. Six-pistons are imbedded into each caliper at the front, with four both sides at the rear. The beefy front brakes saw the M6 overtake many of GT LM and GTD cars under braking, with three cars being overtook at once in some cases at Daytona.