The Horsepower Story
With various aftermarket manufacturers claiming up to 15 horsepower gains with their underdrive pulleys, we set out to the dyno to find out how much power WE could expect on our 1999 ITA-prepped Saturn twin-cam powerplant. The results might surprise you, but here they are.
Because there were no pulleys available at the time, we went to the extreme and actually REMOVED the accessory drive belt (only for one run, of course) to see what the impact would be to ZERO drag due to the accessory drive – sort of pulleys with infinitely small diameters. We figured that if we saw a big gain without a belt, that the pulley gains would be somewhere inbetween, right?
We fired up the dyno and low and behold, removing the belt netted a whopping 3 HP (and we’re rounding UP). That's it. The number was repeatable, and even correlated to data run earlier on the doomed BMW motors - they saw similar results in their application.
So, in light of the fact that 3 HP was completely without a belt, we estimated that the best we could do was to underdrive a few components by 20% - or a theoretical 0.6 HP gain (3 HP x 0.2). After that, it hardly seemed worth it to try to custom fabricate pulleys for less than a 1 HP gain.
I know, I know – stock pulleys, like stock suspension bushings, aren’t sexy, and you can’t brag about them in the pits…but in racing horsepower talks and marketing BS walks. We chalked up this exercise as yet another learning experience in the quest for REAL horsepower. Maybe someday we’ll find some.
Daggar said:This wasn't about a Mustang but I thought it was an interesting read The Horsepower Story
With various aftermarket manufacturers claiming up to 15 horsepower gains with their underdrive pulleys, we set out to the dyno to find out how much power WE could expect on our 1999 ITA-prepped Saturn twin-cam powerplant. The results might surprise you, but here they are.
Because there were no pulleys available at the time, we went to the extreme and actually REMOVED the accessory drive belt (only for one run, of course) to see what the impact would be to ZERO drag due to the accessory drive – sort of pulleys with infinitely small diameters. We figured that if we saw a big gain without a belt, that the pulley gains would be somewhere inbetween, right?
We fired up the dyno and low and behold, removing the belt netted a whopping 3 HP (and we’re rounding UP). That's it. The number was repeatable, and even correlated to data run earlier on the doomed BMW motors - they saw similar results in their application.
So, in light of the fact that 3 HP was completely without a belt, we estimated that the best we could do was to underdrive a few components by 20% - or a theoretical 0.6 HP gain (3 HP x 0.2). After that, it hardly seemed worth it to try to custom fabricate pulleys for less than a 1 HP gain.
I know, I know – stock pulleys, like stock suspension bushings, aren’t sexy, and you can’t brag about them in the pits…but in racing horsepower talks and marketing BS walks. We chalked up this exercise as yet another learning experience in the quest for REAL horsepower. Maybe someday we’ll find some.:
Daggar said:I got it here:
http://www.teamscr.com/pulleys.html
Sure it would be different for other cars. But let's assume for a moment, a car with twice as much HP and even twice as much parasitic loss. That's a whopping 6 HP (which is about as much as I've ever seen on a proven dyno).
Quote:With various aftermarket manufacturers claiming up to 15 horsepower gains with their underdrive pulleys, we set out to the dyno to find out how much power WE could expect on our 1999 ITA-prepped Saturn twin-cam powerplant. The results might surprise you, but here they are.
Because there were no pulleys available at the time, we went to the extreme and actually REMOVED the accessory drive belt (only for one run, of course) to see what the impact would be to ZERO drag due to the accessory drive – sort of pulleys with infinitely small diameters. We figured that if we saw a big gain without a belt, that the pulley gains would be somewhere inbetween, right?
We fired up the dyno and low and behold, removing the belt netted a whopping 3 HP (and we’re rounding UP). That's it. The number was repeatable, and even correlated to data run earlier on the doomed BMW motors - they saw similar results in their application.
So, in light of the fact that 3 HP was completely without a belt, we estimated that the best we could do was to underdrive a few components by 20% - or a theoretical 0.6 HP gain (3 HP x 0.2). After that, it hardly seemed worth it to try to custom fabricate pulleys for less than a 1 HP gain.
I know, I know – stock pulleys, like stock suspension bushings, aren’t sexy, and you can’t brag about them in the pits…but in racing horsepower talks and marketing BS walks. We chalked up this exercise as yet another learning experience in the quest for REAL horsepower. Maybe someday we’ll find some.
fox_bodies_rule said:WOW! real dyno data. Thanks for shedding some light on the subject Daggar I wnet to the site and those guys are serious! I have to also go back to my original comment re. dollar/hp and sign up with DTT92LX's comment about the $25/HP ratio. A set of 185 AFR heads filled with the parts, AFR catolog price $1,375. Assume all is there to support the heads and figure about a 60 hp gain, guess what? $23/hp and some change, not including gaskets and other assorted crap, so round up to $25 dollars! Science and math, what a concept.
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