There are ways to estimate horsepower for standard street cars by looking at the ET and the trap speed and working backwards. The formula will give you a estimated horsepower at the wheels, and then using back of the envelope guestimation to get the drivetrain and fluidic losses, you can work out the horsepower generated at the crank. However, those formulas don't apply to top fuel cars because their drive train is designed to slip continuously all the way down the track. That means you can estimate a horsepower number to the wheels, however, the actual power generated at the crank is completely unknown because most of that power is simply converted to heat as the clutch packs slip and burn away.

Calvin