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*To*: quattro@coimbra.ans.net*Subject*: Wheel h.p. -> crank h.p. conversion???*From*: Luis Marques <marques@rtis.ray.com>*Date*: Wed, 25 Feb 1998 12:26:00 -0600*Reply-To*: marques@rtis.ray.com*Sender*: owner-quattro@coimbra.ans.net

I have been giving some though to the way many people estimate crank hp after doing mods and measuring wheel hp on a dyno and must admit that I'm puzzled. Usually, they make a baseline run before the mod and look at the peak figure and compare it to the claimed peak crank h.p. figure from the manufacturer. Then the come up with a "correction factor" to account for drivetrain losses and use it across the board to estimate new horsepower figures after the mods. Now here is what I don't understand: a stock car may lose 20% of the power to drivetrain losses. Now a tuner does some modifications and the wheel hp is up 15 hp. They then assume that the car is still loosing 20% to drivetrain losses and come up with a claimed power improvement of 19 hp (up from the measured 15 hp number). Now my question: why would drivetrain losses increase as a function of engine power? Aren't drivetrain losses a function of friction more than anything else? In that case they should be almost constant and a measured 15 hp increase at the wheels would be a 15 hp improvement at the crank (not 19 hp). Any takers on this one? Luis Marques '87 4kcsq

**Follow-Ups**:**Re: Wheel h.p. -> crank h.p. conversion???***From:*James Marriott <marriott@micron.net>

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