Auto Racing: engine horsepower, chassis dyno, engine dyno

Question
I may be asking the wrong question to to the wrong person at the wrong time but i don
't who to ask, mabey you canshed some light..  My question is- How does a person figure the total horsepower of an engine ? is there a formula that they use or do they have a machine that measures the horsepower on a guage this is something tahe i have wondered about for a long time and have listened to lots of people who claim to have lots of horsepower or muscle but they don't elaberate on how they know. sometimes i think it might just be wishful thinking...if you can steer me in the right direction ,i would really appreciate the info.. Tks.

Answer
Joey-

  The only real way to determine power and torque is to throw your engine or car on a dyno.  An engine dyno, although more complicated, will give you a specific idea of how much power you're making.  A chassis dyno, one made with the car on rollers, will give a you a decent idea of what kind of power you're making.  You'll have to factor in a 10-20% powertrain loss depending on your transmission and maintainance, but it's fairly accurate.  I like to measure power at the wheels.  It doesn't matter how much power the engine makes if the powertrain sucks up a ton of it.  Then again, a lot of people building engines like to measure it on an engine dyno since the engine's already out of the car.  To each his own, I suppose.  Hope this helps.

Steve