Why is drivetrain loss often expressed as a percentage?
03-08-2006 | 10:41 PM
#1
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Why is drivetrain loss often expressed as a percentage?
Maybe one of the tuners can chime in here. It would seem rational to me that if a car made 300 hp at the crank, but only 225 at the wheels (25% loss), then that same 75 hp loss would apply across the board regardless of modifications or power level. As long as no changes are made in the drivetrain (transmission/diff. gearing, flywheel/clutch weight), then I have always assumed that a 500 crank hp car would make 425 hp at the wheels and not 375 hp at the wheels if you express it as a 25% drivetrain loss. Just curious...
03-08-2006 | 10:44 PM
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why would you only lose only an amount? imagine if the car had 50 hp, would it have -25hp? not plausible.
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Last edited by svek; 02-20-2011 at 01:38 PM.
03-08-2006 | 10:49 PM
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it has to do with friction. friction is not a constant, it's a ratio of several factors. there's friction between the mating teeth of the gears, there's friction in the bearings, there's friction in universal joints, there's friction in wheel bearings, etc...
read here to get an idea of what's going on: http://en.wikipedia.org/wiki/Friction
read here to get an idea of what's going on: http://en.wikipedia.org/wiki/Friction
03-08-2006 | 10:55 PM
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Originally Posted by Galli916
25% of 50hp is not -25whp. It would be 37.5whp.
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Last edited by svek; 02-20-2011 at 01:38 PM.
03-08-2006 | 11:08 PM
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Originally Posted by svek
i was using his theory of the drivetrain losing a constant of 75hp...
It doesn't apply to a VW. My point was to question if the drivetrain loss between stock and modified cars of the same make/model/year was constant or variable as a percentage implies.
03-08-2006 | 11:21 PM
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For those interested... here's a good link. It appears that Corvette owners may be good for something after all.
http://forums.corvetteforum.com/show...1175771&page=2
http://forums.corvetteforum.com/show...1175771&page=2
03-09-2006 | 12:17 AM
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This is a very very flattened dead horse. A quick search on nasioc's archives helps to explain it. In a nutshell RussB has it- it's not a constant, therefore can't be expressed as a percentage OR a single figure like 75 hp.
03-09-2006 | 02:16 PM
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Originally Posted by BAN SUVS
This is a very very flattened dead horse. A quick search on nasioc's archives helps to explain it. In a nutshell RussB has it- it's not a constant, therefore can't be expressed as a percentage OR a single figure like 75 hp.
03-09-2006 | 03:00 PM
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I wish I only lost 75AWHP because of drive-train loss 
I don't really have an inteligent response to say, besides that has already been said where friction isn't a constant
I don't really have an inteligent response to say, besides that has already been said where friction isn't a constant
03-09-2006 | 10:48 PM
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Like these guys have said, friction is main reason for drivetrain losses and is not a constant. It also not an exact percentage. I generally think of it as a sliding scale but in the end its all an estimate. The only way to really get crank hp is by pulling the motor and putting it on an engine dyno. Of course no one does this and in the end it doesn't matter nearly as much as wheel hp anyway. Wheel hp is what actually accelerates your car down the road.
03-09-2006 | 10:50 PM
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Another factor that comes into play is how a Dyno reads.. On one dyno you might read 280AWHP on another you might ready 245AWHP... and then on a dynojet you might read 310AWHP... to many variables come into play
The same track you had your "incident" on?!?!?! 