I've been into cars for several years now, and read a lot of auto magazines, but two terms keep popping up that I've never seen defined. What are "whp" and "bhp?" How are they different from the regular "hp" notation? I've noticed "whp" appears with forced induction. Thanks.

 

whp = wheel horsepower <-- acutal horsepower put to the ground by the drive wheels

bhp = brake horsepower <-- actual power output of the engine under load (not taken at the wheels)

 

that is not right, for a lot of cars you can generally guess a certain percentage of drivetrain loss between your bhp number and your whp number, but it varies for every car and is not the most accurate

 

this is what i got from reading around :

"Wheel horsepower is equal to engine horsepower minus the horsepower it takes to rotate the driveline components. The horsepower absorbed by the driveline due to friction, windage, inertia, rolling resistance etc., results in wheel horsepower readings lower than the actual flywheel hp"

"Typical driveline efficiencies are quoted between 80 and 85% for the average vehicle. By guessing at the driveline efficiency of your car, estimated flywheel horsepower can be determined. For example, if your car produced 300 whp and you estimate the driveline is 80% efficient, the engine would be producing 375 hp (300/0.8 = 375) at the flywheel."

"BRAKE HORSEPOWER is the actual amount of power that an engine can deliver at a certain speed with a wide-open throttle." or dictionary term :

"the power available at the shaft of an engine after minusing the frictional losses in the running component of the engine but before passing through reduction gears or other transmission devices"

so yeah a more detailed explanation of what wrx_ish said lol

- Daniel

 

The first quoted paragraph is correct but the driveline efficiency part is subject to interpretation. That's really nothing more than a 'guesstimate' because the loss from flywheel to drive wheels isn't a linear thing as power is increased or decreased. Don't use those guidelines to figure out HP at the flywheel derived from WHP. I'd be more comfortable using a set value like 70 to 80 HP loss (example) from engine to AWD wheels. It's best to compare apples to apples.


--
0==WW==0
"…axles of evil…" - george w. bush

 

In general I have heard typical driveline losses are 10 to 20%. This varies from car to car and can even vary between the same model of car depending on how worn driveline parts are. Therefore the only way to pinpoint this would be to throw your car on a chassis dyno and then yank the engine and dyno that. You can also figure that due to all wheel drive the wrx is going to be on the higher end of the loss spectrum.

But hey who really cars about numbers...all I know is my car goes like stink.