Bhp vs Hp?

[Edbear]

and back then we thought the slide rule was a miracle compared to using the log tables book.

Ouch! I can remember Log Tables and how the Slide rule was so much harder to pick up on. Then maybe I'm just a simple bloke... Trouble with the calculator at first, was the teachers still wanted you to understand the Maths behind it! So you wound up explaining it anyway. (Not that I'd remember much these days...!)

[avgas]

Stop reading fricken UK Autocar mags....theyre BS, may as well read road and sport if you gonna believe that hype about BHP

[terbang]

Have to dust off me books (when I was an apprentice) for tha one. Just to add to the confusion the output of a turboprop (gas turbine engine) is measured in SHP Shaft Horse Power. Gotta get more books out to revise that one too (drive jet nowadays so I forgot it all). I'll be back..

[Jamezo]

Oh yay, more physics misinformation.

Lets get one thing cleared up: One does not directly measure the power output of a rotating wheel. To do that would require measurement of the actual energy output over time (theoretically possible with a water brake dyno or similar, where the mechanical energy can be converted into thermal energy in a fluid with a known specific heat, the change in temperature measured, and thus the input of energy obtained).

No, what can be measured to a very high precision is torque; the rotational force. By acting against the rotation of the wheel with a known torque, tuned so that it exactly balances the drive from the engine - and thus keeping the rate of rotation constant - you can measure the output torque at a particular rate of rotation.

Measuring the rate of rotation of the wheel is trivial, and can be done by a multitude of methods, the most sensible and accurate being a digital counter on the counter-torque provider.

With those two pieces of information, the power can be calculated, which is the torque multiplied by the rate of rotation. This is the rotational counterpart to the linear concept of power being force multiplied by linear velocity.

These measurements are taken all along the output range of the engine. For automotive purposes, a power plot will be constructed with the engine RPM being a ratio of the wheel RPM, based on the known gear ratios.

[V4ME]

For my money - horsepower is often in the wrist - ask Bayliss