**Re: Re: Drivetrain Losses and 2002 RWHP**
WA 2 FST said:

I have said this before...I call BS on a linear % of power lost through the driveline.

I have reason to believe that the HP lost through the drivetrain is more of a fixed number that will rise a bit as more power is applied...but I don't believe its a percentage.

Case in point: Z06 #1 puts out 350rwhp. It's stock. Z06 #2 puts out 600rwhp. Let's assume car #2 has the same driveline.

Do you think the driveline in car #2 robs 1.71 times the amount of power as the driveline in car #1.

I don't. I think it will rob more power, but not almost twice as much. If car #1 loses 55hp through the drivetrain, I'd say car #2 loses about 70hp. More net power lost, but a much lower percentage of loss.

So, I don't know if your friends' cars are over-rated or not. Maybe the driveline is loosening up some, there's not as much friction/heat buildup and its more efficient now...but the motor is still around 405 flywheel HP? Or maybe indeed they have strong motors. It's all a guess, IMHO.

I tend to agree with you, but I don't know what the real relationship is.

Here is some engineering viewpoint about this issue. If the friction in the driveline is a constant (which may not quite be the case, but lets say it is for now), then the HP losses in the driveline will increase linearly with increased RPMs. In other words, if you could put a torque measuring device on the input side of the driveshaft and measure how many ft-lbs it took to make the whole system just start turning, then that would be the torque required to overcome the system's inherant friction. Lets say that torque measured out to be 50 ft-lbs (a number I'm just pulling out of my hat

) and remains constant. Lets also assume that the car is in 4th gear on the dyno, where the ratio is 1:1 which will make the drive shaft and axles turn at the same RPM as the engine. If the tranny is not in 4th gear, then half of the driveline will be turning at a different speed vs. the other half, and this could change the total HP loss throught the system.

So, using the baseline I setup above, how much HP is lost?

A Z06 in 4th gear will make the driveshaft/tranny/axles turn at 1:1 with the engine RPMs. HP = (T x RPM)/5252. This formula can also be used to find the HP loss, using T as the constant frictional torque of 50 ft-lbs above.

At 0 RPMs there is 0 driveline HP loss.

At 3000 RPMs there is a 28.6 HP loss.

At 6000 RPMs there is a 57.1 HP loss.

You can already see that this is a linear relationship. Obviously, the HP curve of any engine is usually not linear, but has a peak hump somewhere before its red-line RPM, then falls off with increased RPMs. But if you could measure the HP loss in a manner like I described above, then you could determine the % loss at any given point along the RWHP curve -- and it would not be a linear % of the HP at any given point.

Of course the point of most interest would be at the peak HP RPM, and this is the point which the 15% 'standard' is assumed to occur at for the C5

-- the same point where peak FWHP would be produced.