FYI - Follow up. Several of you said depending on the drive-train..anywhere from a factor of .80 - .85 should be used on average. One guy said that he knows some experience dude that said no matter what car it was there was only like a 15hp difference between whp and rwhp. I thought that was BS. Well, here's the dyno on the new zr-1...guess what...REAL close to the 15-20 PERCENT drive-line loss NOT 15HP.
"It always happens this way. Shortly after a new performance car is released to the public, it will find its way to a dyno shortly thereafter. When that new vehicle is the new performance king of the automotive world, aka the 2009 Corvette ZR1, our collective interest is piqued. So, how does it fare on the rollers? Two separate 'Vettes were tested, and the average output was about 535 horsepower at the rear wheels. After factoring in the normal 15-percent drivetrain losses for a rear-wheel drive car, that's pretty darn close to the claimed 638. " - corvette blogger.com
"It always happens this way. Shortly after a new performance car is released to the public, it will find its way to a dyno shortly thereafter. When that new vehicle is the new performance king of the automotive world, aka the 2009 Corvette ZR1, our collective interest is piqued. So, how does it fare on the rollers? Two separate 'Vettes were tested, and the average output was about 535 horsepower at the rear wheels. After factoring in the normal 15-percent drivetrain losses for a rear-wheel drive car, that's pretty darn close to the claimed 638. " - corvette blogger.com