Horsepower Calculator
Turn your time slip into an estimated power figure. Choose 1/8 or 1/4 mile, enter total race weight, then add ET, trap speed, or both. Compare estimated flywheel and rear-wheel horsepower from each method.
Your pass
Estimated horsepower
Enter race weight and at least one performance value to calculate.
From trap speed
Add MPH to calculate this estimate.
From elapsed time
Add ET to calculate this estimate.
ET and MPH are calculated separately. Their results are not averaged.
Track-based estimates are not dyno measurements. Launch traction, shifting, converter or clutch slip, aerodynamics, weather, and changing boost or nitrous delivery can affect the result. Rear-wheel HP is derived from your assumed drivetrain loss.
Drivetrain-loss guide
Use these broad rear-wheel-drive comparison ranges to choose a starting assumption. They are not a measurement or a universal correction for a particular transmission.
| Combination | Assumed total loss | How to use it |
|---|---|---|
| Manual, clutch fully holding | 12–18% | 15% starting scenario. A slipping clutch is not covered by a normal manual estimate. |
| Automatic with efficient coupling or converter actually locked during the run | 15–20% | 18% starting scenario. A well-matched converter can transfer power efficiently. |
| Automatic with a non-lockup performance converter | 20–25% | 22% starting scenario. Try the lower and upper values to see how much the result changes. |
| Automatic with substantial coupling loss or a poorly matched converter | 25–30% | 27.5% high-loss scenario. Use as a sensitivity check, not proof that the converter is bad. |
Converter slip % is not drivetrain-loss %. Stall speed alone does not determine efficiency: a high-stall converter can still couple well at speed. These percentages include the transmission, converter where applicable, driveshaft, rear axle and the rest of the power path.
Actual loss varies with load, RPM, temperature, gearing and test method; an efficient automatic can overlap a manual. The selector fills in a sample percentage and you can adjust it.
Background: AUTOLAB Performance on wheel-power estimates and Car Craft's engine/chassis test and converter-slip discussion. The converter-specific bands above are illustrative scenarios, not test-certified ranges.
How the estimates are calculated
These empirical drag-strip relationships estimate flywheel horsepower from total race weight in pounds, ET in seconds, or trap speed in MPH. The eighth-mile mode uses its own coefficients; it does not convert your run to an assumed quarter-mile pass.
Quarter mile
Flywheel HP from ET = weight × 200 ÷ ET³
Flywheel HP from MPH = weight × (MPH ÷ 234)³
Eighth mile
Flywheel HP from ET = weight × 52 ÷ ET³
Flywheel HP from MPH = weight × (MPH ÷ 187)³
Rear-wheel estimate
Rear-wheel HP = flywheel HP × (1 − drivetrain loss ÷ 100)
The flywheel estimate stays unchanged when you adjust loss. Only the derived rear-wheel figure changes. Results are rounded to whole horsepower for display.
Formula reference: Robert Szabo, Horsepower from Racecar Weight & Speed (PDF). These are general racing estimates; they are not calibrated to a particular LT1 combination or chassis dyno.
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