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u/ibrahimumer007

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▲ 74 r/MechanicalEngineering

BHP vs WHP - Is Brake Horsepower measured at the crankshaft or at the wheels?

I'm a mechanical engineering student, and a friend and I disagree on what Brake Horsepower (BHP) actually means.

My understanding is:

  • IHP = Power developed inside the cylinders.
  • BHP = Power measured at the crankshaft using an engine (brake) dynamometer.
  • FHP = IHP − BHP (internal mechanical losses).
  • WHP = Power measured at the driven wheels using a chassis dynamometer, after drivetrain losses.

My friend argues that BHP is measured at the wheels, saying that's the only power that really matters.

Most engineering textbooks and references I've checked define BHP as crankshaft power, but I also found a few automotive websites claiming BHP is measured at the wheels.

Questions:

  1. Is BHP, by engineering definition, always measured at the crankshaft?
  2. Is my friend simply confusing BHP with WHP?
  3. Why do some automotive sources incorrectly describe BHP as wheel horsepower?
u/ibrahimumer007 — 10 days ago