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Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 01-19-2009, 03:27 PM   #1
IFX
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Question about horsepower..

I wanted to know if there was a special formula to determine the amount of power to the wheels on a stock car?

Such as my FX has 280 at the crank, but around 220 to the wheels. Give or take about 10 horsepower..

Would this be fair for me to say that the M3 has around 310-315 to the wheels?
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Old 01-20-2009, 12:16 AM   #2
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Originally Posted by IFX View Post
I wanted to know if there was a special formula to determine the amount of power to the wheels on a stock car?

Such as my FX has 280 at the crank, but around 220 to the wheels. Give or take about 10 horsepower..

Would this be fair for me to say that the M3 has around 310-315 to the wheels?
Check your math. FX: 220/280 = .78. About right for an auto-box.

Can figure on better efficiency for the manual box in the M, say 83%.

333HP (crank) x 0.83 = 276 WHP. Factory states 262. YMMV

In any case, nowhere near 310 WHP. Best folks are getting for non-FI M3's is at or near 300 WHP. Claims beyond that are rare and questionable

>>flame suit on<<<
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Old 01-21-2009, 03:43 PM   #3
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Thank you for your input.. How accurate is that 83 percent?
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Old 01-21-2009, 05:13 PM   #4
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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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