Question 1

What is the horsepower formula from torque?

Accepted Answer

HP = Torque (lb-ft) × RPM / 5,252. The constant 5,252 comes from unit conversion: 1 HP = 33,000 ft-lbf/min = 550 ft-lbf/s; dividing by 2π converts from rotational to linear: 33,000 / (2π × 60) ≈ 5,252.11. For 300 lb-ft at 4,000 RPM: 300 × 4000 / 5252 = 228.5 HP.

Question 2

What is the difference between horsepower and torque?

Accepted Answer

Torque is rotational force — how hard the engine twists. Horsepower is the rate of doing work — how fast the engine applies that torque. High torque at low RPM (diesel engines) pulls heavy loads from a standstill. High HP at high RPM (performance gasoline engines) sustains high speeds. HP = Torque × RPM / 5,252.

Question 3

At what RPM do HP and torque cross?

Accepted Answer

HP and torque (in lb-ft) are always equal at 5,252 RPM — this is a mathematical identity from the formula. Below 5,252 RPM, torque exceeds HP; above 5,252 RPM, HP exceeds torque. Looking at a dyno curve, the crossover point is always at 5,252 RPM regardless of engine type.

Question 4

What is the difference between BHP and WHP?

Accepted Answer

BHP (Brake Horsepower) is measured at the engine flywheel on a engine dynamometer. WHP (Wheel Horsepower) is measured at the driven wheels on a chassis dyno, after drivetrain losses (transmission, driveshaft, differential friction). WHP is typically 15–20% less than BHP for manual transmissions; 20–25% less for automatics.

Question 5

How accurate is HP calculated from torque and RPM?

Accepted Answer

The formula is mathematically exact if your torque and RPM measurements are accurate. Real-world dyno measurements have ±2–5% variability due to temperature, atmospheric pressure, and load variation. Most performance dyno runs take 3–5 pulls and average the results for reliability.

Engine Horsepower Calculator