HP Calculation/Formula
Thread Starter
USMC (retired)
Joined: Aug 2004
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From: Wimauma FL
HP Calculation/Formula
First question - is Braking Horsepower (BHP) the same as when someone says crankshaft horsepower (I guess that is HP from the engine not the rear wheels?)
second question - How does one calculate what the engine HP is when in comparison to a rear wheel HP? Example, if one says he has lets say 500RWHP, what does that calculate to on the engine? What is the formula? Another example is the Z06, they say it is 505HP, but we all know that the rear wheel HP is different.
second question - How does one calculate what the engine HP is when in comparison to a rear wheel HP? Example, if one says he has lets say 500RWHP, what does that calculate to on the engine? What is the formula? Another example is the Z06, they say it is 505HP, but we all know that the rear wheel HP is different.
Safety Car
Joined: Jan 2001
Posts: 4,386
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From: Boise ID
BHP is the measure of an engine's horsepower without the loss in power caused by the gearbox, differential, water pump, and other auxiliary components such as alternator, power steering, and AC compressor.
Auto manufactures use SAE (what we normally refer to as FWHP), this reflects the rated power of the engine at the flywheel in as-installed trim, with all accessories and standard intake and exhaust systems (still minus drive train losses).
As far as drive train losses to the rear wheels? Well, this is always debated as there are too many variables to have a simple calculation. Could probably safely say the drive train loss to be in the area of 12 to 18%, depending if a manual or auto trans (manual being the more efficient).
Auto manufactures use SAE (what we normally refer to as FWHP), this reflects the rated power of the engine at the flywheel in as-installed trim, with all accessories and standard intake and exhaust systems (still minus drive train losses).
As far as drive train losses to the rear wheels? Well, this is always debated as there are too many variables to have a simple calculation. Could probably safely say the drive train loss to be in the area of 12 to 18%, depending if a manual or auto trans (manual being the more efficient).
Melting Slicks
Joined: Jun 2004
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From: Newark, DE
St. Jude Donor '06
http://en.wikipedia.org/wiki/Horsepower#Brake_horsepower_.28bhp.29 http://en.wikipedia.org/wiki/Horsepower#SAE-certified_horsepower
Originally Posted by D C
second question - How does one calculate what the engine HP is when in comparison to a rear wheel HP? Example, if one says he has lets say 500RWHP, what does that calculate to on the engine? What is the formula?
Yes, you can use the manufacturer's SAE rating and subtract the measured rwhp to determine drivetrain loss. That only holds true for a stock output motor though.
Melting Slicks
Joined: Feb 2007
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From: New Smyrna Beach Florida
As stated, the % drivetrain losses will vary as HP increases. I've read average values for 6 speeds of 15% and 20% for automatics stock. Not sure of either one and as stated, these percentages will change as hp is increased. As an example, to calculate rwhp for a stock 6 speed 1-.15 = rwhp/350 so for a 350 hp rated engine you would expect to see 350 hp x .85 = 297 rwhp.
Team Owner
Joined: Sep 2003
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From: Raleigh / Rolesville NC
As stated, the % drivetrain losses will vary as HP increases. I've read average values for 6 speeds of 15% and 20% for automatics stock. Not sure of either one and as stated, these percentages will change as hp is increased. As an example, to calculate rwhp for a stock 6 speed 1-.15 = rwhp/350 so for a 350 hp rated engine you would expect to see 350 hp x .85 = 297 rwhp.
Even if you take 15% drive line loss, that would be APPROX. 500 rwhp x 1.15 = 575 FWHP.
Next big question is DOES THAT LOOK RIGHT? 575 on an NA 2002 or newer LS6 motor? No I dont think soo.
The last question is Dynos are for tunning purposes only, Comparing dyno numbers on different cars run on different days, on different machines is meaningless, Unless you want bragging rights.
Safety Car
Joined: Oct 2004
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From: Plano TX
Another factor not mentioned is the rear suspension power loss.. Independent rear suspension (all corvettes) have more of power loss than cars with a solid rear axle, such as a Camaro SS or Trans Am WS6.. This can be seen on a dyno.. The LS-1 puts down more horsepower to the wheels than the same LS-1 in the Corvette. The horsepower rating is claimed to be 323 horsepower at the crank vs 345-350 for the same engine in our Corvettes. a Bone stock LS-1 in a C5 will make between 285-310 hp depending on the year and transmission.. The same engine in a Camaro or Trans-Am makes a little bit more due to the solid rear axle not robbing as much horsepower as our independent suspension.. Our C5's have a 200 pound lighter weight advantage, which gives us a slight advantage overall at the race track
