Calculate Engine Crank Horsepower from Wheel Horsepower and Drivetrain Loss
Formula:
The Drivetrain Conversion Formulas
- WHP to Crank HP Formula: Crank HP = WHP / (1 − Loss Percentage)
- Crank HP to WHP Formula: WHP = Crank HP × (1 − Loss Percentage)
Understanding WHP vs. HP (Crank Horsepower)
When measuring vehicle output parameters, automotive builders categorize power outputs into two distinct metrics: Engine Horsepower (Crank HP/BHP) and Wheel Horsepower (WHP). Engine horsepower represents the raw force calculated directly at the flywheel before any parasitic auxiliary structures drain energy. Conversely, WHP identifies the net power left to propel the car after moving through the complete transmission assembly.
Why Do Cars Lose Horsepower Between the Engine and Wheels?
This drop in total power is known as drivetrain loss or parasitic loss. As rotational energy moves from the engine flywheel through mechanical parts, friction and inertia absorb a portion of that energy. The key components responsible for this power drop include:
- The torque converter or clutch system assembly.
- Internal transmission gear meshing setups and hydraulic pumps.
- The driveshaft, universal joints, and differential ring/pinion gears.
- Wheel hub bearings, brake rotor drag, and heavy tire configurations.
Standard Mechanical Drivetrain Loss Estimates
| Configuration | Average Loss Factor | 300 Crank HP Yields | To Hit 300 WHP You Need |
|---|---|---|---|
| Front-Wheel Drive (FWD) | 10% - 12% | ~270 WHP | ~333 Crank HP |
| Rear-Wheel Drive (RWD) | 15% | 255 WHP | 353 Crank HP |
| All-Wheel Drive (AWD) | 20% - 22% | 240 WHP | 375 Crank HP |