Wheel hp or crank hp, with a realistic range
1/4 Mile Estimator
This estimator is built for the situation most people are in: you have a dyno sheet showing wheel horsepower, or only an educated guess. Pick the power basis, and it converts to crank power before predicting your time.
- 1/8-mile ET
- 7.40 sec
- 1/8-mile speed
- 94.4 mph
- Trap speed
- 190.0 km/h
- Weight per hp
- 7.79 lb/hp
- Conservative ET (Huntington)
- 12.47 sec
- Conservative trap (Huntington)
- 113.0 mph
What the estimator assumes
The estimator treats the car as an ideal power-to-weight machine: constant power, no traction loss, shifts done on time. That is why the first number reads as the optimistic case. The Huntington-based figure beneath it, with constants 6.290 for ET and 224 for MPH, is what a less-than-perfect run tends to look like.
For example, 3,300 lb and 360 wheel hp on a rear-wheel-drive car converts to about 424 crank hp. The calculator predicts 11.55 s at 118.0 mph, with a conservative case of 12.47 s.
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.
Wheel hp to crank hp assumptions
| Drivetrain | Typical loss | Crank = wheel ÷ |
|---|---|---|
| Front-wheel drive | 12% | 0.88 |
| Rear-wheel drive | 15% | 0.85 |
| All-wheel drive | 20% | 0.80 |
These are rules of thumb, not measurements for your car. Automatics, big tyres and heavy driveline parts push loss higher. The WHP to HP calculator lets you set a custom figure.
Using the estimate to plan an upgrade
Because the formula uses a cube root, gains get smaller as you add power: going from 300 to 400 hp at 3,500 lb saves 1.21 seconds, but 400 to 500 hp saves only 0.86. Shaving weight has the same pattern.
Frequently asked questions
What is the difference between this and the main calculator?
The numbers come from the same formula. This page is set up for wheel horsepower and for planning, with a rear-wheel-drive dyno figure pre-filled.
Why is my real ET slower than the estimate?
Traction, tyres, gear ratios, shift points and air density all matter. A conservative second figure is shown for that reason.
Can I estimate a bigger turbo build?
Yes. Enter your target crank horsepower and race weight. Remember that more boost also demands traction you may not have.
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