A few things are clear from these numbers. But much is unclear as well. The table below
ASSSUMES we see a similar hp loss in the E92 M3 compared to the E60 M5.
- Torque and power losses are definitely rpm dependent and software like CarTest captures this effect. Losses are predicted as linear across a given rpm range from a minimum number to a maximum. The loss numbers I list in the table are min/max numbers across in a max acceleration run in 2nd gear.
- The 335i is clearly under-rated. We all know this. The drivetrain loss at peak hp and peak torque loss is just too low. However, it only takes a stated crank hp number of 312 hp to get to the M5 drivetrain loss number.
- The massive losses of the RS4 AWD system on both tq and hp is clear
- The hp losses for the E46 M3 seem too high. This car has performance figures that hint at a bit of under-rating as well but the transmission losses point to an over-rating
- CarTest software NAILS the 0-60, 1/4 mi time and trap speed perfectly for the RS4 (test ref.) CT/actual 4.6/4.6, 13.2/13.2, 104/104. Note the great agreement between average CT predicted hp loss and measured peak loss. Anyway you look at the losses CT matches better on the RS4 than any of the BMWs.
- CarTest generally uder-predicts performance for E46 M3, E60 M5 and 335i but still does quite well for the E92 M3 despite the disparity in CT losses vs. measured losses
I have nor included any loss predictions for the 335i from CarTest as becuase mentioned in a previous post no matter how much I tweak hp and tq numbers I can't get a good simulation vs. actual from CarTest. The known under-rating doesn't help...