How do I calculate horsepower at the crankshaft using wheel horsepower?
A. When running a car on a dyno (dynamometer), one measures horsepower and torque at the wheels. To precisely calculate your actual horsepower at the crankshaft (also known as brake horsepower (bHP)) is close to impossible due to the unknown drivetrain losses (friction, heat, and lubrication in bearings, gears, couplings, and shafts all account for loss of HP). No two vehicles are alike, i.e., some have stronger engines with high drivetrain losses and some have weaker engines with low drivetrain losses and so on. Through testing and experience, a safe approximation is to assume between 15-18% drivetrain losses in a RWD vehicle. To calculate, simply use the following equation (assume 17% drivetrain loss): bHP = ( (wheel HP) / 0.83 ) .
