Keep the model coefficient visible
Our worksheet uses ET = 5.825 × (weight in pounds / mechanical horsepower)^(1/3). The coefficient encodes a model assumption rather than a physical constant. Race-ready weight includes driver and fuel. Keep the power definition consistent when comparing cases, and treat the output as a scenario rather than a time-slip promise.
ET(s) = 5.825 × (race weight_lb / mechanical HP)^(1/3)Follow the worked comparison below for the input units and assumptions.
Work through an example
For 3,200 lb and 400 hp, the weight/power ratio is 8. Its cube root is 2, so the model yields 11.65 seconds. Inverting the same equation with those inputs returns 400 hp; this checks algebra, not real-world predictive accuracy.
Use race-ready weight and a consistent power basis
Include driver, fuel and equipment in the entered weight. Keep wheel or engine power definitions consistent across scenarios rather than comparing a measured wheel figure with an unrelated engine rating. The worksheet does not determine an unknown drivetrain efficiency.
Use sensitivity comparisons instead of extra decimals
The model scales ET with the cube root of weight divided by power. A 10% power increase multiplies estimated ET by (1/1.10)^(1/3), about 0.9687. That model change does not account for a different launch or shifting behavior.
Compare quarter-mile scenarios with the coefficient visible
Fix race-ready weight at 3,200 lb and compare model horsepower inputs. The ET coefficient is held at 5.825. These are empirical model outputs, not promised passes, and the table does not simulate the launch or changes in traction.
ET(s) = 5.825 × (race weight_lb / mechanical HP)^(1/3)- Include driver, fuel and equipment in race-ready weight.
- Keep the same power definition across every compared case.
- Calculate the weight/power quotient and take its cube root before multiplying by the coefficient.
- Use observed time slips to assess whether the model is representative; a reversible algebra check alone does not validate its prediction.
| Race weight (lb) | Model horsepower | Empirical ET (s) |
|---|---|---|
| 3200 | 300 | 12.822 |
| 3200 | 400 | 11.65 |
| 3200 | 500 | 10.815 |
The 400 hp case produces 11.65 seconds because 3,200/400 equals 8 and its cube root is 2. Increasing model power by 25% to 500 hp reduces the model ET by less than 25%, reflecting the cube-root relationship. That sensitivity should not be interpreted as a guaranteed improvement from an engine modification.
Check the inputs before interpreting a difference
Reaction time is separate from ET. Weight, power basis and the chosen empirical coefficient should stay visible in a comparison. Extra decimal places in the output do not remove uncertainty from traction, shifts, weather or the model itself.
Before you apply the result
Traction, aero drag, gearing and power delivery can materially change ET. Reaction time is separate from elapsed time. The dial-in worksheet summarizes actual passes and does not convert this empirical estimate into a reliable bracket-racing prediction.
Try the calculation
Enter your own values in the related calculators. Compare one input at a time and keep units and operating conditions visible with the result.
Frequently asked questions
Does the quarter-mile ET estimate include reaction time?
No. Reaction time is separate from the elapsed time of the pass.
Is 5.825 a physical constant?
No. It is the coefficient used by this empirical comparison model. It does not calibrate the model to your vehicle.
Can I use estimated ET as a bracket-racing dial-in?
It is a provisional scenario. Use representative actual passes and track conditions when interpreting a dial-in worksheet.
Can I use the ET formula backward to check its horsepower input?
Yes. Algebraically invert the same coefficient-based equation and it should return the original horsepower. This checks consistency of the calculation, not predictive accuracy for the vehicle.
Reference and method
Hale coefficient model: ET constant 5.825 and speed constant 234. Lucius documents the formulas and compares them with road-test data. These are empirical relationships, not physical laws or calibrated vehicle predictions.
Jeff Lucius / Stealth 316 — Quarter-mile formulas and original regression analysis ↗These explanations and examples describe the documented model. No manufacturer testing, named expert authorship or independent professional review is claimed. Read the method policy or report a correction.