auto drivetrain losses- what %?
Team Owner
Joined: Mar 2000
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From: Boston, MA
It isn't a perfect science, but we typically use 18% as the figure. If you were on a dyno the torque values are nearly impossible to believe due to the TC slip unless you are in 3rd gear with the torque convertor locked up.
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Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
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Originally Posted by qwiketz
8-12% seems super low.
There is alot more variance in LT1 dyno results than L98s. Some people have strong LT1s that put more down than they should.
Safety Car
Joined: Apr 2003
Posts: 3,793
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From: VA
Originally Posted by vader86
Only if you believe the factory crank hp ratings.
Fact is, when people "convert" their RWHP to FWHP, they then compare it to the factory advertised HP, not some hypothetical larger HP which was used to justify a larger drivetrain loss %. If you want to use 18% loss for an LT1 then you need to use 330 FWHP as the baseline for your mods. Nobody does that.
The real drivetrain loss is bound to be higher than 8-12%, but given how people use this "conversion" it is a more apples-to-apples number than 18%
In the end, all that a chassis dyno tells you is RWHP. If that much...
Last edited by VenkmanP; Jul 19, 2005 at 04:28 AM.
Melting Slicks
Joined: May 2001
Posts: 3,014
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From: Raleigh, NC
I think % loss is BS. Here's why. Say I have a car that makes 300 RWHP. With 20% drivetrain loss that's 60 HP, 360 FWHP. Say I put a 100 HP N20 kit on my car. Now it makes 400 RWHP. According to the same theory, my drivetrain now takes 80 HP to turn. How the hell does adding an N20 kit make my drivetrain harder to turn? So much so that it requires an additional 20 HP? It doesn't, percentages are BS.
Why someone can not build a drivetrain in a controlled environment and use an electric motor to see exactly how much power it takes to turn is beyond me. Use a ZF6 mated to a proper length drivetrain, D44, halfshaft's, wheels and tires. Put the wheels on rollers, similar to a dyno, and add the rolling resistance based on weight and aerodynamics of the vehicle. Presto, an exact number.
What they make at the flywheel is more of a sales tool than relevant number anyway. The torque produced at the wheels is what you feel press you into the seat when you jam on it.
This is just my opinion, so flame on if you must.
Why someone can not build a drivetrain in a controlled environment and use an electric motor to see exactly how much power it takes to turn is beyond me. Use a ZF6 mated to a proper length drivetrain, D44, halfshaft's, wheels and tires. Put the wheels on rollers, similar to a dyno, and add the rolling resistance based on weight and aerodynamics of the vehicle. Presto, an exact number.
What they make at the flywheel is more of a sales tool than relevant number anyway. The torque produced at the wheels is what you feel press you into the seat when you jam on it.
This is just my opinion, so flame on if you must.
Safety Car
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From: [Quote=WOEII] Is dried brown doodie powders man! [/Quote]
Originally Posted by neat
I think % loss is BS. Here's why. Say I have a car that makes 300 RWHP. With 20% drivetrain loss that's 60 HP, 360 FWHP. Say I put a 100 HP N20 kit on my car. Now it makes 400 RWHP. According to the same theory, my drivetrain now takes 80 HP to turn. How the hell does adding an N20 kit make my drivetrain harder to turn? So much so that it requires an additional 20 HP? It doesn't, percentages are BS.
I have always thought this. Increasing power is not going to increase drivetrain loss. If my 300 CHP engine is dynoing 240 RWHP (20% loss), should my 1000 CHP engine dyno 800 RWHP? The more power you have the less of a percentage of loss you will have because it takes a set amount of power to rotate your drivetrain.
In depth testing would be a great idea but I think a stock vehicle on the dyno gives a pretty good indication of the actual amount of power needed for the drivetrain.
If it takes 60 Ft Lbs of torque from an engine making 300 Ft Lbs to rotate your drive line, it's only going to take 60 Ft Lbs of torque from an engine making 500 Ft Lbs of torque to rotate your drive line.
I am by no means an expert but I don't see how any figure can be applied in a linear fashion to percentage of loss. If I am wrong somebody please pipe up because I'd really like to know.
Edit:
Vader86 put it very simply, "At our power levels". Damn had I read the whole thread I could of just quoted and posted
.Lesson learned.
Last edited by Upstate; Jul 19, 2005 at 09:15 AM. Reason: Reading is fundamental
Team Owner
Joined: Sep 2001
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From: Athens AL
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Right, we only start with percentages but this is not really the case, it approaches a constant value as your crank power goes up.
Racer
Joined: Jul 2001
Posts: 399
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From: Toronto Ontario
Originally Posted by Upstate
I have always thought this. Increasing power is not going to increase drivetrain loss. If my 300 CHP engine is dynoing 240 RWHP (20% loss), should my 1000 CHP engine dyno 800 RWHP? The more power you have the less of a percentage of loss you will have because it takes a set amount of power to rotate your drivetrain....
Is this not one of the reasons why drive train loss is a % of power?
Last edited by vette_tweak; Jul 19, 2005 at 12:30 PM.
Team Owner
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From: Athens AL
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Originally Posted by Hot Rod 90
it would be interesting to know generally when the percentage figure fades and the constant value begins to dominate when coming up with an estimate.
Everything is a potential variable, which is why I wouldnt even attempt to calculate it. It would be a separate Ph.D. dissertation in itself. HP isnt linear, viscosity changes with temp, inertia moments of every single part of the drivetrain, friction with certain materials, etc.
Pro
Joined: Feb 2005
Posts: 658
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From: Centerville OH
I have always thought this. Increasing power is not going to increase drivetrain loss. If my 300 CHP engine is dynoing 240 RWHP (20% loss), should my 1000 CHP engine dyno 800 RWHP? The more power you have the less of a percentage of loss you will have because it takes a set amount of power to rotate your drivetrain.
In depth testing would be a great idea but I think a stock vehicle on the dyno gives a pretty good indication of the actual amount of power needed for the drivetrain.
If it takes 60 Ft Lbs of torque from an engine making 300 Ft Lbs to rotate your drive line, it's only going to take 60 Ft Lbs of torque from an engine making 500 Ft Lbs of torque to rotate your drive line.
In depth testing would be a great idea but I think a stock vehicle on the dyno gives a pretty good indication of the actual amount of power needed for the drivetrain.
If it takes 60 Ft Lbs of torque from an engine making 300 Ft Lbs to rotate your drive line, it's only going to take 60 Ft Lbs of torque from an engine making 500 Ft Lbs of torque to rotate your drive line.
I hope this makes sense .......
