Engine Horsepower Calculator
Estimate how much horsepower your engine really makes from drag-strip data. Enter vehicle weight with driver and your quarter-mile elapsed time for the classic Fox elapsed-time estimate, then cross-check against the trap-speed method using your finish-line mph.
TheCalculators — Engine Horsepower Calculator
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Estimated Horsepower
265 hp
Fox elapsed-time method · 3,300 lb running 13.5 s
- Vehicle Weight
- 3,300 lbs
- Quarter-Mile ET
- 13.5 s
- Trap Speed
- 100 mph
- HP — ET Method
- 265
- HP — Trap-Speed Method
- 258
- Average of Both
- 261
- Power-to-Weight
- 160.7 hp per ton
How the estimate is built
- 1Fox formulaHP = weight ÷ (ET ÷ 5.825)³
- 2Normalize ET13.5 ÷ 5.825 = 2.318
- 3Cube it2.318³ = 12.448
- 4Divide weight3,300 ÷ 12.448 = 265 hp
- 5Trap-speed check3,300 × (100 ÷ 234)³ = 258 hp
Method comparison
Estimates reflect crank (flywheel) horsepower assuming a typical drivetrain. Wheel horsepower is usually 12–18% lower with an automatic and 10–15% lower with a manual. NHRA correction factors for altitude, temperature and humidity are not applied.
Most useful next
Formula
HP = weight ÷ (ET ÷ 5.825)³ · cross-check: HP = weight × (trap mph ÷ 234)³
Pro tips
- • Remove every pound you can — weight appears directly in the numerator.
- • Trap speed reacts faster to power changes than ET, which is dominated by launch and traction.
FAQ
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