A Simpler Explanation Of The Measurement Of ONE HORSE POWER

jharrell wrote:

pnichols wrote:


I've always thought that the diesel owners thought that their rigs pulled better because they didn't have to rev the engine very high to tap the engine's horsepower. Kindof a preference thing, not really based on engineering facts.

The V10 in our small motorhome will paste me back into the seatback if I punch it, but it takes 4000-5000 RPM to do it.

You can get any torque number you want at the wheels through gearing, horespower cannot go up (only goes down through losses from engine to wheels). Gears exchange RPM for torque. Your diesel engine puts out 1000 lb-ft of torque, who cares, I can get 10000 out of a lawnmower engine with the right gears.

You cannot measure power directly, dynos measure rpm and torque to derive horsepower. Torque is meaningless on its own, it requires the rpm component to get a meaningful measurement of power.

Many of those here should recognize this relationship as the same one between volts, amps and watts. Watts are power (746 per hp in fact), volts is equivalent to torque and amps equivalent to rpm. Using a transformer/coil you can exchange one for the other but watts stays the same. Just think your spark plug gets 20000v from a 12v system through a coil, you can get 20000 lb-ft of torque from a 12 lb-ft motor through gears.

Again you don't measure watts directly either, you measure voltage and current to derive power.

Good explanation.

There are inertia dynos that measure HP by measuring the acceleration of a heavy drum that the drive wheels turn. Math determines the HP that was required to change the drum’s RPM from speed X to Y. Similarly you could measure electrical watts by heating a measured amount of water to a measured temperature change over time. Now a typical watt meter does what you suggest which is voltage and current.