It has been quite accurately determined over many many many thousandsof dynos that the C5/C6 drivetrain has an approx. 12% power loss when measured on DynoJet rolling road dynos.
385bhp = ~335rwhp
405bhp = ~355rwhp
436bhp = ~390rwhp
505bhp = ~450rwhp
The %age may be slightly reduced as the crank HP increases - but on a 1000bhp setup, there is close to a 120hp power loss to the wheels.
I would not be surprised that in the end, once someone takes the GT-R motor to an engine dyno, theyw will find that there is closer to a 20% or higher drive train loss on a static dyno setup, but that by conventional calculaiton this loss is less and also variable under load on the road.
