There's really only one way to get an accurate measure of a car's horsepower, and that's by strapping it on a proper dyno. Even then, not all dyno's produce the same results, but in our numbers-driven society, we'll take what we can get. Two of the fiercest 'Ring competitors are the new Corvette ZR1 and the Dodge Viper ACR, which currently holds the unofficial fastest lap record with a blistering time of 7:22.1. Wondering how they stack up power-wise? According to reports on DragTimes, the duo are pretty darn close with the naturally-aspirated Dodge posting an impressive 546 horsepower and 510 lb-ft of torque compared to the supercharged ZR1's 549.9 horsepower and 500 lb-ft.
Considering that both vehicles use a six-speed stick and power the rear wheels, drivetrain losses should be similar, so these figures are relatively comparable and they prove once again that the horsepower wars are alive and well. For what it's worth, Dodge officially (under) rates the ACR at 600 horsepower, and an estimated 15% loss through the drivetrain would put this beast at an actual 642 horses.