How this calculation works
The elapsed-time formula uses how long the run took. The trap-speed formula uses speed near the finish. Each uses its own editable empirical calibration, so compare them with the assumptions stated.
ET estimate = weight × (ET constant / elapsed seconds)^3. Trap estimate = weight × (trap mph / speed constant)^3.A worked example
At 3,200 lb and 117 mph with a speed constant of 234, the trap estimate is 3,200 × 0.5³ = 400 hp.
Good to know
Empirical quarter-mile approximations. Traction, grade, weather, drivetrain losses and timing equipment can materially affect estimates. Use a dynamometer for measured output.
How the inputs affect the result
Use total race weight with driver and fuel. Compare repeated runs under similar conditions before reading much into the difference between the two estimates.
Holding trap speed fixed leaves that estimate unchanged.
Where the calculation applies
Empirical quarter-mile approximations. Traction, grade, weather, drivetrain losses and timing equipment can materially affect estimates. Use a dynamometer for measured output.
For a related calculation, see the Torque RPM and horsepower calculator.
A few questions, answered
Why can the elapsed-time estimate be lower?
A poor launch can add elapsed time even when the car reaches a similar trap speed. Because the estimate cubes the ratio, the added time has a substantial effect.
What does the “Same speed with a slower launch” setting illustrate?
Holding trap speed fixed leaves that estimate unchanged.