Thread: M3 Dynotest
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      09-08-2007, 06:44 PM   #19
First Lieutenant

Drives: X6 50i/2008 X5 4.8i
Join Date: Jan 2006
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Originally Posted by devo View Post
The disparity of power -applied to the pavement- between the 335 and new M is less than the disparity of the claimed power. One of two, (or both) things occurred; that BMW has understated the 335's power much more than the M; assuming that the M is even understated. Secondly, the 335 has less drivetrain loss; the former is the more likely.

Regardless, the drivetrain loss of the M is very minimal. In other words, it's putting down some serious power. A typical drivetrain loss might average 15%; the M has lost only 10%, or like I said, BMW underestimated the M's power as well.

As you can see, the RS4 doesn't get a good percentage of power to the ground. One reason is that it's AWD has a parasitic effect on power; robbing another 5%, or so. Not to trash Audi, but the chart is not to impressive.

The 335 and M5 are excellent examples.
Drive train losses are not a fixed percentage, but rather fixed number.
Parasitic Torque losses= Friction coefficient X Rotating Mass X Radius.
Frictional coefficient is higher at lower RPM, and does change with RPM.
By using lighter materials in the transmission, you can reduce the drive-train losses.

Audi has higher losses because the rotating mass (Quattro drive train) is more than the that o RWD system.