1. What is Crank Horsepower?

Crank Horsepower (also called flywheel horsepower) is the power output measured at the engine's crankshaft before any drivetrain losses. It represents the engine's true power output before any power is lost through the transmission, differential, and other drivetrain components.

2. How Does the Calculator Work?

The calculator uses the following equation:

Where:

• \( Wheel\_HP \) — Horsepower measured at the wheels (hp)
• \( Loss\_fraction \) — Fraction of power lost in the drivetrain (decimal)

Explanation: The equation accounts for power loss between the engine and wheels by dividing the measured wheel horsepower by (1 minus the loss fraction).

3. Importance of Crank HP Calculation

Details: Knowing crank horsepower helps in comparing engine performance across different vehicles, tuning engines, and understanding drivetrain efficiency. It's especially important for performance modifications and dyno testing.

4. Using the Calculator

Tips: Enter wheel horsepower measured from a dynamometer test and the estimated drivetrain loss fraction (typically 0.15 for RWD, 0.20 for FWD, 0.25 for AWD). All values must be valid (Wheel_HP > 0, 0 ≤ Loss_fraction < 1).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical drivetrain loss fraction?
A: Typical values range from 15% (0.15) for rear-wheel drive to 25% (0.25) for all-wheel drive vehicles.

Q2: Why is crank HP higher than wheel HP?
A: Crank HP is measured before drivetrain losses, while wheel HP is measured after power is lost through transmission, differential, and other components.

Q3: How accurate is this calculation?
A: It provides a good estimate but actual losses can vary based on drivetrain condition, temperature, and other factors.

Q4: Can I use this for motorcycles?
A: Yes, though motorcycle drivetrain losses are typically lower (10-15%) due to simpler drivetrains.

Q5: Where is crank HP typically measured?
A: Engine manufacturers measure crank HP on an engine dynamometer with no drivetrain components attached.