Quote:
Originally Posted by upsidedownfunnel
These driveline loss estimates are nowhere near an exact science. The 15% number bandied about is actually not accurate. Different cars with different differentials, final drives, transmissions, transfer cases, wheels, etc. all will vary in how much loss they have. That's why when you see a tuner estimate the bhp "assuming" a 15% driveline loss, that is complete B.S.
The reason most just use percentages is because things like the differential, transmission, and the general durability/weight of these components are probably matched to the power output of the vehicle. A smaller car would have lighter components since heavier components would be unnecessary and slow the car down more.
Also, as engine power goes up, a lot of these loss forces are amplified which is why using a percentage is more appropriate than a fixed power figure. However, even this is not totally correct as these changes are not perfectly linear. So the loss is really dynamic and even depends on which gear you're in.
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Good post and good points. That said, I'd expect the driveline losses for the M40I to be between 10-15% ;-)
....it's just an approximation to give us a rough idea of what the chassis dyno numbers translate to in net crank hp.
Cheers,
Dave