There is quite a good write up on this in the latest Practical Performance Car.

I will try my best....

Basically, Imagine a really stiff wheel on a vertical post. (ie the flywheel)

Now imagine a bar fixed to this wheel in order to turn the wheel that is say one foot long. Now imagine putting one pound of pressure on the bar in an attempt to turn the wheel. This would be one Pound per Foot of pressure (ie 1 lb/ft). So if you applied 10 lbs of weight on the end of the same bar, then you then have 10 lb/ft of load.

Now this is important - note that the above has not yet turned our wheel.

Techincally, that means that no work has been done (sad isnt it!) Even if you struggle with it all day with lots more weight - if it doesnt move, then it is not a measurement of work.

Work is the measurement of how far it moves. If you manage to move one pound 33,000 ft in one minute, then you have acheived work, and more specifically, one Horse Power!.

One Horse Power = moving one pound 33,000 feet.

In an engine, the movement is round and round, rather than in a straight line! As such we talk about revolutions (also known as RPM!)

So now you have the torque from the flywheel, and the amount it moves in a given amount of time frame. This gives you the engine horse power!

Power is a result of torque.

So what is Break Horse Power?

This is simply the torque of an engine measured by a tool called an engine brake. What the machine does is effectively try to stop the engine from turning, and then measures how much effort it takes to slow the engine down. When the engine can no longer accelerate, but also does no longer deccelerate, then you have a reading that provides you with a measurement of the engine torque. The BHP is then a calculation based on the the rest!

Clear as mud!


JJ