According to Patrick Hale's formula: to calculate the engine horsepower of a vehicle, enter the 1/4 mile trap speed in mph and the weight in lbs. Hit the Calc Horsepower button to obtain the estimated value. 

The Trap Speed method involves the measurement of the speed of a vehicle at the end of a fixed distance run (usually the distance is taken as 1/4 of a mile). Note: The total weight of the vehicle including the occupants and fuel loading over the trap speed run should be used when estimating the vehicle horsepower. References: Power to Weight Ratio calculator. Engine Displacement Formula calculator. Auto Math Handbook, J Lawlor, ISBN13: 9781557880208. 
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