Calculate horsepower from torque and RPM, convert between HP and torque, and estimate wheel horsepower with drivetrain loss
Horsepower and torque are the two fundamental measurements of engine performance. While they're related, they measure different aspects of an engine's capability. Horsepower measures the rate at which work is done, while torque measures the rotational force produced by the engine.
The relationship between horsepower and torque is defined by the formula: HP = (Torque × RPM) / 5252. This constant (5252) comes from the conversion factors between the units used. Understanding this relationship helps you interpret dyno charts and engine specifications more effectively.
| Engine Type | Typical HP Range | Typical Torque | Peak RPM |
|---|---|---|---|
| 4-Cylinder | 150-250 HP | 150-200 lb-ft | 5,500-7,000 |
| V6 | 250-350 HP | 250-300 lb-ft | 6,000-7,500 |
| V8 (NA) | 350-500 HP | 350-450 lb-ft | 5,500-7,000 |
| V8 (Supercharged) | 500-800 HP | 500-700 lb-ft | 6,000-7,500 |
| Diesel V8 | 300-450 HP | 600-900 lb-ft | 3,000-4,500 |
Not all engine horsepower reaches the wheels. Power is lost through the transmission, driveshaft, differential, and other drivetrain components due to friction and mechanical inefficiency. Understanding these losses helps you estimate real-world performance.
An engine produces 300 lb-ft of torque at 4,000 RPM. Calculate the horsepower:
HP = (300 × 4,000) / 5,252 = 228.5 HP
This shows that at 4,000 RPM, the engine is producing approximately 229 horsepower.
An engine produces 400 HP at 6,000 RPM. Calculate the torque:
Torque = (400 × 5,252) / 6,000 = 350.1 lb-ft
At peak horsepower, the engine is producing approximately 350 lb-ft of torque.
A RWD car has 450 HP at the crank with 15% drivetrain loss:
Wheel HP = 450 × (1 - 0.15) = 382.5 HP
The car puts approximately 383 horsepower to the ground, losing 67.5 HP through the drivetrain.