Horsepower from Quarter-Mile Trap Speed
The dyno-free power check a racer runs off the timeslip.
Example
You enter
- Vehicle weight incl. driver (lb) 3200
- Quarter-mile trap speed (mph) 108
You get
- Estimated horsepower 315
- Companion 1/4-mile ET 12.6 s
Checked against published worked examples from: Stealth 316 (Hale 1986 formula).
Details, formula, and sources
ScopeHale's HP = weight x (mph/234)^3 inverts the quarter-mile trap speed to horsepower. A 3,200 lb car trapping 108 mph made about 315 hp at the flywheel (Hale / Wallace Racing define it as crank power) (companion ET 12.6 s); a 7 mph faster trap (115 mph) implies 380 hp, a 20% jump - the cube law that makes trap speed, not ET, the cleaner power indicator. Empirical fit to typical cars, flywheel power, not a substitute for a dyno. A hobbyist estimate; the actual dyno measurement governs.
Formula or tableHP = weight x (mph/234)^3; ET = 5.825 x (weight/HP)^(1/3).
Source and editionHale's empirical quarter-mile relations HP = weight x (mph/234)^3 and ET = 5.825 x (weight/HP)^(1/3), as compiled in the drag-racing references, by name.
Free accessHale's quarter-mile relations are public empirical results widely used in the drag-racing community.
What governsEstimate. AHJ and licensed professional govern.
API field namesweight_lb, trap_mph, hp, et_s
- Trap-speed power HP = weight x (mph/234)^3, a cube-law fit to the power-to-weight ratioHale quarter-mile relation
- ET companion ET = 5.825 x (weight/HP)^(1/3) cross-checks the estimateHale quarter-mile relation
- Empirical a statistical fit estimating flywheel (crank) power; not a dyno measurementdrag-racing practice