Critical Thinkers - is drivetrain loss really a percentage?
05-22-2005, 11:15 AM
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Critical Thinkers - is drivetrain loss really a percentage? I raised this issue awhile ago, and I just want to see what everyone else thinks. Read on....
It has always been said that drivetrain losses are given by a percentage. For instance a car uses 15% of the flywheel hp/tq to get to the rear wheels for a given power level. So a 350hp (at the crank) car would get approximately 297rwhp. I'll go along with that for argumentative purposes. It's using 48ish hp to drive the car.
However, let's assume that this particular car has a 9". spec s3 clutch, aluminum driveshaft, bogarts w/ mt slicks, billet steel flywheel, and m6 of course that is pro-shifted (i.e. heavy duty).
So on this car, let's say you swap motors, with a 383 stroker w/ a solid-roller cam, 18 degree heads, victor manifold and a 150shot of the good stuff. On an engine dyno we'll say that the motor pulls 700hp at the crank. So by the initial way of thinking this car would have 595rwhp. Losing the 15% of power at the crank, resulting in a 105hp loss through the same drivetrain as before.
The question I am trying to answer is "is drivetrain loss really a percentage?" It would seem to me, that without changing the drivetrain or any other inertia related items in the driveline, that the car would still only lose approximately the same hp throught the drivetrain to get to the wheels. So in theory the new motor would make 652rwhp (700 - 48= 652). Does this make sense or am I missing some variable that cause drivetrain losses to be a percentage?
What I would like to see if they are out there, is somebody's dyno graph of a chassis dyno then another dyno graph of an engine dyno after some serious modding to the motor alone, no drivetrain mods!, has been made. Then another chassis dyno after the motor has been reinstalled in the same car, again with no drivetrain changes. If anyone has any of these that would be much appreciated. Maybe this can be sticky material....:-).
Okay lets hear your thoughts!!!
It has always been said that drivetrain losses are given by a percentage. For instance a car uses 15% of the flywheel hp/tq to get to the rear wheels for a given power level. So a 350hp (at the crank) car would get approximately 297rwhp. I'll go along with that for argumentative purposes. It's using 48ish hp to drive the car.
However, let's assume that this particular car has a 9". spec s3 clutch, aluminum driveshaft, bogarts w/ mt slicks, billet steel flywheel, and m6 of course that is pro-shifted (i.e. heavy duty).
So on this car, let's say you swap motors, with a 383 stroker w/ a solid-roller cam, 18 degree heads, victor manifold and a 150shot of the good stuff. On an engine dyno we'll say that the motor pulls 700hp at the crank. So by the initial way of thinking this car would have 595rwhp. Losing the 15% of power at the crank, resulting in a 105hp loss through the same drivetrain as before.
The question I am trying to answer is "is drivetrain loss really a percentage?" It would seem to me, that without changing the drivetrain or any other inertia related items in the driveline, that the car would still only lose approximately the same hp throught the drivetrain to get to the wheels. So in theory the new motor would make 652rwhp (700 - 48= 652). Does this make sense or am I missing some variable that cause drivetrain losses to be a percentage?
What I would like to see if they are out there, is somebody's dyno graph of a chassis dyno then another dyno graph of an engine dyno after some serious modding to the motor alone, no drivetrain mods!, has been made. Then another chassis dyno after the motor has been reinstalled in the same car, again with no drivetrain changes. If anyone has any of these that would be much appreciated. Maybe this can be sticky material....:-).
Okay lets hear your thoughts!!!
05-22-2005, 11:59 AM
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Here's some reading....while it's good to rehash, might as well post these instead of doing the typical "regurgitation as original thought" internet thang. 
http://web.camaross.com/forums/showt...threadid=81279
http://web.camaross.com/forums/showt...threadid=53126
http://web.camaross.com/forums/showt...threadid=81279
http://web.camaross.com/forums/showt...threadid=53126
05-22-2005, 01:25 PM
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Hmmm....so from what I get, the more power an engine has, the more friction there is in the same drivetrain that was in the car before the power had been increased. Therefore, the exact same drivetrain eats up more power than before due to bearings, gears, other drivetrain components being stressed (for lack of a better word) more. I guess I can see that....its just odd that it will eat up that much more hp. I guess it's time someone designs an ultra-strong bearing setup, gear setup that won't deflect, or cause greater friction. Also, rear end coolers would be a sweet addition....back to the drawing board!
