Some horsepower math
Le Mans Master
Joined: Nov 2009
Posts: 6,119
Likes: 156
From: Huntington tx
As usual the discussion about horsepower ratings is purely subjective and really tough to nail down precisely.
Manufacturers advertise engine HP numbers not RWHP numbers, i.e. the bigger the number the bigger the bragging rights. Guys/Gals who build their engines usually have RWHP numbers from dyno testing and then the math comes into play to inflate that number to compare apples to apples on how much the gain in engine HP they got. But in the end it's not ever definitive to precise actual output cause that is just a snap shot at that time.
My car was on the dyno and during the testing it ran a 522rwhp but it had fuel problems (pressure) and consequently the numbers were handicapped. So even with 522 it wasn't an actual depiction of power when the dyno itself started the power readings from a MINUS -25hp then up to 522hp. So generally it only gives you a fairly good guessing point. After fixing fuel delivery issues and taking that -25hp and adding that back into the initial max number.......it's still only an estimate of 550-600 rwhp and even that is just like pie in the sky, temperature affects the real numbers too.
So when someone asks what you got under the hood(powerwise) the discussion starts with either engine HP or RWHP.
And end the end..... when you are benchtop racing, usually guys like to inflate a little/or a lot, and keeping the numbers rounded off is ok in my book. That's the fun in having a discussion with like minded guys/gals!!!!
Manufacturers advertise engine HP numbers not RWHP numbers, i.e. the bigger the number the bigger the bragging rights. Guys/Gals who build their engines usually have RWHP numbers from dyno testing and then the math comes into play to inflate that number to compare apples to apples on how much the gain in engine HP they got. But in the end it's not ever definitive to precise actual output cause that is just a snap shot at that time.
My car was on the dyno and during the testing it ran a 522rwhp but it had fuel problems (pressure) and consequently the numbers were handicapped. So even with 522 it wasn't an actual depiction of power when the dyno itself started the power readings from a MINUS -25hp then up to 522hp. So generally it only gives you a fairly good guessing point. After fixing fuel delivery issues and taking that -25hp and adding that back into the initial max number.......it's still only an estimate of 550-600 rwhp and even that is just like pie in the sky, temperature affects the real numbers too.
So when someone asks what you got under the hood(powerwise) the discussion starts with either engine HP or RWHP.
And end the end..... when you are benchtop racing, usually guys like to inflate a little/or a lot, and keeping the numbers rounded off is ok in my book. That's the fun in having a discussion with like minded guys/gals!!!!
Burning Brakes
Joined: Jul 2010
Posts: 959
Likes: 50
From: Peters Colony Republic of Texas
[W]hen someone asks what you got under the hood(powerwise) the discussion starts with either engine HP or RWHP.
And end the end..... when you are benchtop racing, usually guys like to inflate a little/or a lot, and keeping the numbers rounded off is ok in my book. That's the fun in having a discussion with like minded guys/gals!!!!
And end the end..... when you are benchtop racing, usually guys like to inflate a little/or a lot, and keeping the numbers rounded off is ok in my book. That's the fun in having a discussion with like minded guys/gals!!!!
The Lizzard
Le Mans Master
Joined: May 2013
Posts: 5,798
Likes: 181
From: Pueblo, CO
Wasn't just GM, it was an SAE standards switch (possibly government mandated). The old SAE 'gross' HP was measured at the crank with no accessories; 'net' is also at the crank, but with the engine more-or-less as-installed.
Details here: http://en.wikipedia.org/wiki/Horsepower#SAE_gross_power
Details here: http://en.wikipedia.org/wiki/Horsepower#SAE_gross_power
