Estimate your engine's real horsepower.
Work out engine output three ways: from a quarter-mile ET, from trap speed, or straight from torque and RPM. Then see the split between crank horsepower at the flywheel and wheel horsepower at the tires, plus kW and PS.
The estimate
The ET, trap speed and torque methods estimate crank (flywheel) horsepower. Wheel horsepower is what a chassis dyno reads after drivetrain losses.
What the numbers mean
Crank horsepower vs wheel horsepower
Where the power goes
How output scales with the input
Output scorecard
Estimate table
Crank and wheel horsepower across a range around your input.
| Trap speed | Crank HP | Wheel HP | kW | PS |
|---|
Engine horsepower, explained
How Engine Horsepower is Calculated
Engine horsepower depends on displacement, RPM, volumetric efficiency, and Brake Mean Effective Pressure (BMEP). The simplified formula is HP = (Displacement x RPM x VE x BMEP) / 792,000. BMEP varies by engine type: naturally aspirated engines typically produce 125-150 psi, turbocharged engines 200-300 psi, and supercharged engines 175-225 psi.
Naturally Aspirated vs Forced Induction
Naturally aspirated (NA) engines rely on atmospheric pressure to fill cylinders, limiting power to what displacement and RPM can achieve. Turbocharged engines use exhaust gases to spin a compressor, forcing more air into cylinders and significantly increasing power. Superchargers work similarly but are belt-driven from the crankshaft, providing immediate boost without turbo lag.
Horsepower vs Torque
Horsepower measures the rate at which work is done, while torque measures rotational force. They are related by the formula: HP = Torque x RPM / 5,252. At 5,252 RPM, horsepower and torque are always equal. Below that RPM, torque is higher; above it, horsepower is higher. Torque determines acceleration feel, while horsepower determines top speed potential.
Common questions
What is volumetric efficiency?
Volumetric efficiency (VE) is the percentage of cylinder volume actually filled with air-fuel mixture during each intake stroke. A naturally aspirated engine typically achieves 80-90% VE. Forced induction (turbo/supercharger) pushes VE above 100% by cramming in more air than atmospheric pressure alone could provide.
Why does turbocharging increase power so much?
Turbocharging increases the amount of air entering the engine by compressing it before it enters the cylinders. More air means more fuel can be burned, producing more energy per combustion cycle. A turbo can effectively double the BMEP of an engine, dramatically increasing power output from the same displacement.
What is BMEP?
Brake Mean Effective Pressure (BMEP) is the average pressure in the combustion chamber during the power stroke that produces useful work at the crankshaft. It is a measure of engine efficiency independent of displacement. Higher BMEP means more power per liter of displacement. Modern turbo engines achieve BMEP above 300 psi.
How accurate is this calculator?
This calculator provides a reasonable estimate based on general engineering formulas and typical BMEP values. Actual engine output depends on many factors not captured here, including fuel type, ignition timing, compression ratio, camshaft profile, and exhaust flow. Dyno testing is the only way to measure true engine output accurately.
Estimates for planning only. ET and trap-speed formulas (Hale and Fox) assume a well-prepped car, good traction and typical air. Real output depends on gearing, tire size, altitude, fuel, weather and how the run was made. A dyno is the only way to measure true horsepower.