E46Fanatics - View Single Post - Question about horsepower..
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Old 01-21-2009, 05:13 PM   #4
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Join Date: Apr 2002
Location: Houston
Posts: 286
My Ride: '00 323iT / S54 6Spd
Originally Posted by IFX View Post
Thank you for your input.. How accurate is that 83 percent?
Good Question! You'll see various numbers quoted for manual and automatic cars. Manuals typically assumed @ 15% - 17% loss (83% - 85% efficient). Automatics 17% to 20% loss.

We're talking about the power lost to friction in the drive train from the crankshaft to the rear tires.....any gears meshing, sliding surfaces (shaft spinning in bushing), ball/roller bearing, you get the idea. The auto tends to be a bit less efficient at power transfer than a manual.

If you're interested in learning more there are tons of threads here & elsewhere (check the FI forum in particular) that get into the mechanics of dyno tests and the challenges involved in making rear wheel power measurements that accurately reflect crank (engine) HP.

Have fun
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