RWHP vs. Crank HP?

GREATWHITE666

Registered User
Hey guys, im always trying to tell what hp number are, and people are always saying the RWHP. so i see like all these billions of mods and some are only pushing like 250RWHP, so what would the hp be at the engine? is there any way to tell how much horsepower you lose by the time it gets to the back wheels assuming most driveline parts are stock? like a 95 SC is 230hp, but by the time it reaches the back it's like under 200 isnt it?. that so unfair!
:mad:
-Damon
 
Drivetrain Loss

Generally speaking I have heard that standard lose somewhere between 12-17% and Autos usually lose 20-25%. That is just what it takes to spin everything that the motor has to in order to get the power to the wheels . . . when it comes to racing the RWHP is the number that matters.

Dave
 
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For Super Coupes I've always heard 13-15% drivetrain losses for a manual transmission and 18-20% for automatics with locking converters and 25% for non-locking converters.

To convert rear wheel numbers to at the crank numbers, you would divide the rear wheel numbers by the remainder of 100%.

For example a manual transmission pulling 310 rwhp and assuming a 15% drive train loss would be calculated as follows.

310 divided by .85 = 364.7 at the crank.

To calculate rwhp when the crank HP is known or advertised, multiply instead of dividing. In the case of a stock 94/95 SC with manual transmission the math works like this.

230 X .85 = 195.5 at the wheels.

There are lots of variables, but most advertised numbers will be at the crank averages and then factored to an SAE standard. Factoring accounts for temp, elevation, humidity and maybe a few other things.

Like Dave said, it's what you get to the ground that really matters.

David
 
i see

Wow, can't believe so much is lost. It's like it just disappears... I can see why front wheel drive cars have an easier time. Interesting, thanks guys.
-Damon
 
It happens in front drive cars . . .

It happens in front drive cars as well . . . they have a transaxel to spin, and they eat just as much hp as a rear drive car . . . to compound that most transaxels will not hold up to big torque like a rear drive set up can.

Dave
 
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