How is horsepower actually measured for both wheel horsepower and brake horsepower? And are there limits to the technology that measures them?
In: Engineering
Horsepower is measured with a dynamometer which is any device that can measure torque and rpm at the same time.
For wheel horsepower it’s a pair of drums that the car sits on top of that work kindof like a car treadmill. (With the car held firmly in place to keep it from jumping off) A very basic dyno will just be a heavy known weight and by measuring rpm vs time you can tell how much power is generated by how quickly the drum spins up. Usually though it’s a motor/generator which can provide variable resistance and can calculate HP by measuring how much power is generated.
Similar thing with brake horsepower though usually that’s done with a motor mounted on a stand outside of a car with the motor bolted to the dynamometer.
Torque, the twisting force the engine can make, is measured, either by hooking the engine itself up to a measurement device (brake), or running the car on rollers (wheel). Wheel will always be less because there is loss through the drive train between the engine and the wheels.
Horsepower is calculated from torque and rpm: Horsepower = Torque x RPM / 5252.
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