Considering the differences between the old P84 and the modified version, it could have been something truly insane.7. P85
2005 initially saw BMW pursuing a new approach aimed at increasing power while
simultaneously further reducing weight and lowering the centre of gravity. One
option investigated was larger V angles of 100° and 110°. The larger the V angle,
the lower the engine’s centre of gravity. However, this is accompanied by reduced
lateral bending stiffness and also by an increase in the overall width of the engine.
This limits the vertical installation space, which is then insufficient to achieve
efficient flow characteristics in the exhaust gas system. The 90° V angle was
therefore retained.
The P85 concept was revolutionary: cylinder spacing was further reduced to 102
mm and bore was increased to 98 mm, giving a wall thickness between cylinders
of just 4 mm. The cylinder head and piston bore formed a single casting, thus
dispensing with the highly stressed cylinder head gasket. The crankcase was
machined from solid. The crankshaft, with a clutch diameter of 99 mm, was
positioned just 52 mm above the lower surface of the engine. Long tie rods
connected the rudimentary crankcase with the cylinder head/cylinder unit. The
overall height of the P85 was 30 mm less than its predecessor.
The P85 also marked a big advance in thermodynamic terms. In parallel with
conventional manifold injection, BMW also developed a direct petrol injection
system, with corresponding combustion process. This was abandoned, however,
when it was announced that the regulations would limit injection pressure to 100
bar.
The engine had been designed and fine-tuned for a lifetime of 800 km, but a
sudden rule change now threw the preparations into chaos. One and the same
engine now had to be used for two race weekends running, i.e. it would have to be
capable of covering 1,600 km. This was too much of a risk with a new – and
“extreme” – engine concept. So the P85 project was stopped and instead the
existing P84 was revised to meet the new endurance requirements.
10+hp (950hp)
2kg´s lighter (84kg!)
6mm lower CoG (118mm)
for the modified P84.
