Calculation Method
Input Values
Performance Results
Horsepower
281
HP
Torque
320
lb-ft
1/4 Mile
13.50
seconds
Trap Speed
101
mph
Power-to-Weight
161 HP/ton
Est. 0-60 mph
6.5 sec
HP per lb
0.080
Formulas Used
From Quarter Mile Time
HP = (Weight / ET³) × 197.5
Buschur formula
From Trap Speed
HP = Weight × (Speed / 234)³
From Torque
HP = (Torque × RPM) / 5252
HP and Torque cross at 5252 RPM
Power-to-Weight
HP/ton = (HP / Weight) × 2000
Performance Class Reference
| Class | HP Range | HP/Ton | 1/4 Mile | 0-60 mph |
|---|---|---|---|---|
| Economy | 100-150 | 50-80 | 17-19s | 10-13s |
| Family Sedan | 150-250 | 80-120 | 15-17s | 7-10s |
| Sports Car | 250-400 | 150-250 | 13-15s | 5-7s |
| Muscle Car | 400-600 | 200-300 | 12-13s | 4-5s |
| Supercar | 600-800 | 300-400 | 10-12s | 3-4s |
| Hypercar | 800+ | 400+ | <10s | <3s |
Power Unit Conversions
1 HP (mechanical)
= 745.7 Watts
1 HP (metric/PS)
= 735.5 Watts
1 kW
= 1.341 HP
1 lb-ft
= 1.356 Nm
Quick Answer
Horsepower = (Torque x RPM) / 5252. This formula uses torque in lb-ft. Example: 300 lb-ft at 4000 RPM = (300 x 4000) / 5252 = 228 HP. Conversions: 1 HP = 0.746 kW = 1.014 PS (metric HP). Peak HP and peak torque occur at different RPMs; they cross at 5252 RPM.
Key Facts
- HP = (Torque in lb-ft x RPM) / 5252
- Torque and HP curves cross at exactly 5252 RPM
- 1 HP = 745.7 watts = 0.746 kW
- 1 HP = 1.014 PS (metric horsepower)
- Brake HP (BHP) = measured at engine
- Wheel HP (WHP) = measured at wheels (10-15% drivetrain loss)
- 1 HP = ability to lift 550 pounds 1 foot in 1 second
- Torque accelerates; HP determines top speed
Frequently Asked Questions
What is horsepower?
Horsepower (HP) measures the rate at which work is done. One mechanical horsepower equals 550 foot-pounds per second or 745.7 watts. In cars, it determines how fast the engine can move the vehicle, affecting acceleration and top speed.
What is the difference between HP and torque?
Torque is rotational force (measured in lb-ft or Nm), while HP is the rate of applying that force. HP = (Torque × RPM) / 5252. Torque provides initial acceleration; HP maintains speed. "Torque wins races, HP sells cars."
What is wheel HP vs crank HP?
Crank HP (gross) is measured at the engine crankshaft. Wheel HP (WHP) is measured at the wheels after drivetrain losses. Typically WHP is 15-20% less due to transmission and differential friction. Dyno numbers are usually WHP.
How do I calculate quarter mile time?
Use the formula: ET = (Weight/HP)^(1/3) × constant. Weight should include driver. Actual times vary with traction, altitude, temperature, and driver skill. Professional times use weight with driver and half tank of fuel.
What is a good power-to-weight ratio?
Economy cars: 50-80 HP/ton. Sports cars: 150-250 HP/ton. Performance cars: 250-400 HP/ton. Supercars: 400+ HP/ton. Formula 1: ~1000 HP/ton. Higher ratios mean faster acceleration.