The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
brake horsepower
NOUN: abbr. bhp or b.hp. The actual or useful horsepower of an engine, usually determined from the force exerted on a friction brake or dynamometer connected to the drive shaft
Wythors is correct but I'd like to elaborate if I may
BHP is the indicated HP of the engine on an ENGINE dynamometer (not a chassis dyno) This is without any power robbing accessories such as power steering pumps, alternators and a/c compressors attached.
For all practical purposes it is Bull**** horsepower, because it means nothing in the real world.
The bottom line is that Brake HP is your paycheck BEFORE taxes.
Brake HP is what car makers usually advertise.
Hey...iut's the biggest number and is a "real" measurement, right?
Riiiight.....
RWHP is the real thing, at the tire, no BS
This is why "260 BHP" cars make 190 at the tire on a cassis dyno.
Any doubts on this?
I'm installing two brand new Superflow chassis dynos tomorrow =o)
Ones is a 2WD and the other AWD I've spent some time studying.
BHP is fun and such for fine tuning and advertising, but all we really care about is what happens at the tire =o)
Heres some good definitions (not webster definitions):
Indicated Horsepower
This represents the power developed in the engine cylinder as obtained from the pressure in the cylinders. This is pressure obtained from an indicator which shows cylinder pressures. Indicated horsepower does not represent the actual useful power delivered by the engine.
Brake Horsepower
This is the actual horse power delivered by the engine to the shaft. It is equal to the "indicated horsepower" less the friction of the engine. It is useful horsepower and is also called the "shaft horsepower".
(Remember, this is with an engine out of the car with no accessories attached)
Effective Horsepower
This is the final horse power delivered to equipment. An engine may be operating compressors, pumps and auxiliary equipment as part of its own power production needs, and the remaining power is therefore the effective power for drive. The difference between indicated horsepower and effective horsepower may be as much as 25%.
Rear Wheel Horsepower
Horsepower available to the rear wheels of the vehicle measured on a chassis dynamometer.