View Single Post
      03-13-2007, 01:39 AM   #21
DrM
Second Lieutenant
United_States
29
Rep
225
Posts

Drives: 2007 335i Montego Blue E90
Join Date: Dec 2006
Location: Mars

iTrader: (0)

Quote:
Originally Posted by catm3 View Post
Those formulas work OK initially for a rough estiamte, but I hate when they are applied to a modified car. The driveline loss stays constant unless you change something in the driveline. It just boggles my mind when tuners claim 800+hp kits for a car putting 6xx hp to the wheels because they are applying that same percentage loss.
Actually, the driveline losses depend upon several factors but are definitely a function of RPM. The higher the RPM, the larger the losses.

But given that BMW estimates the losses at 13% on the manual transmission and that they estimate the car at 300 ft.lbs. that works out to between 40 and 45 horsepower taken by the drivetrain. That should work out to be roughly the same losses no matter how much someone modifies the horsepower of the engine.

So, I agree with you. Adding 45 horsepower to someone's dyno number is probably a lot closer to reality than adjusting for the 13%. Shiv's car put 405 ft.lbs. to the ground so I would say his car is probably really making about 450.
Appreciate 0