Horsepower from 1/4 mile trap speed and ET
HP Estimator
No dyno? Your time slip is a power meter. Enter your weight, trap speed and optionally ET, and this estimator returns the crank and wheel horsepower your run implies.
- Crank hp from ET
- 363 hp
- Weight per hp
- 9.63 lb/hp
- Power in kW
- 271 kW
Why trap speed reveals horsepower
Trap speed depends on power and weight but barely on launch, so it is the better power indicator. The inverse formula is HP = weight × (MPH ÷ 234)3. A 3,500 lb car trapping 110 mph is making about 364 hp by this method. If the ET-based figure is much lower, you are losing time at the launch.
The estimate uses the widely published Patrick Hale equations: ET = 5.825 × (weight ÷ hp)1/3 and MPH = 234 × (hp ÷ weight)1/3, with weight in pounds and hp measured at the crank. They are documented, along with the more conservative Huntington (6.290 / 224) and Fox constants, in Stealth316’s horsepower / ET / MPH calculator notes. See the full formulas and sources page.
Trap speed to horsepower table (3,500 lb)
| Trap speed | Crank hp | Wheel hp (RWD) |
|---|---|---|
| 90 mph | 199 | 169 |
| 100 mph | 273 | 232 |
| 110 mph | 364 | 309 |
| 120 mph | 472 | 401 |
| 130 mph | 600 | 510 |
| 140 mph | 750 | 637 |
Limits of the method
This is an estimate. It reflects the whole car (aerodynamics, gearing, traction at speed) not only the engine. It also depends on how accurate your weight is. Use a dyno for the real figure, and the slip estimate to sanity-check it. Also see the WHP to HP converter.
Frequently asked questions
Can I estimate horsepower from quarter-mile time?
Yes, with HP = weight × (5.825 ÷ ET)³, but trap speed is typically more reliable than ET.
How accurate is a horsepower estimator?
Within roughly 5–10% for a clean pass, depending on weight accuracy and conditions.
Is the number crank or wheel?
The formula gives crank hp. A wheel horsepower figure is shown using a drivetrain loss assumption.
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