Horsepower from Quarter-Mile Trap Speed
The dyno-free power check a racer runs off the timeslip: Hale's HP = weight x (mph/234)^3 inverts the quarter-mile trap speed to horsepower. A 3,200 lb car trapping 108 mph made 315 hp at the wheels (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, wheel power, not a substitute for a dyno. A hobbyist estimate; the actual dyno measurement governs.
Formula and source
HP = weight x (mph/234)^3; ET = 5.825 x (weight/HP)^(1/3).
Hale'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.
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