Drivetrain HP loss??
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Racer
Joined: Jan 2002
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From: Spanish Fork UT
Drivetrain HP loss??
I have been told/taught (perhaps incorrectly) that HP loss through the drivetrain is based on an approximate number rather than a %. Is this true or false. I always figured that my car which dynoed at 412rwhp would have around 460fwhp or in other words around 50hp loss through the drivetrain. I am having a discussion with a guy about how much fwhp a Vette would have if it was putting 1000hp to the ground. He says about 400hp lost through the drivetrain and I say no where even close to that. What say ye mighty experts???
Race Director
Joined: Jun 2000
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From: I don't have to show you any stinkin' badges
Re: Drivetrain HP loss?? (Horsepower)
15% loss for manual, about 18% for automatic is what is bantered around on this forum. Someone, much more technical than me is going to have to supply you with the answer as to why it is a percentage rather than a fixed horsepower number for drivetrain loss. Example: 340 rwhp/.85 = 400 hp at the crank. :chevy
Melting Slicks
Joined: Mar 2001
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From: New Milford CT
Re: Drivetrain HP loss?? (Horsepower)
Quote: HP loss through the drivetrain is based on an approximate number rather than a %. Is this true or false?
There was a huge post on this about 9 months ago, I wish I could find it. We even had an aircraft Jet engine dyno engineer give us some ins and outs on the subject!
I look at it this way. Say the Z06 405 fwhp is correct. They dyno at about 350/355 rwhp stock. So the loss is about 13%. So you can divide by .87 to get and approximate fwhp figure from a rwhp figure.
The drive line loss is a % because of the increase loss of hp to friction and rotating mass as the gross hp increases. Think of it this way, as the hp goes to say 500 rwhp, the friction in the driveline DOES NOT stay the same! It goes up to! Those gears etc, are grinding together harder and getting hotter!
That is why the loss is a percentage. Whether the percentage stays at a constant 13% is another question, I doubt that it does. But that seems like a good figure for Vette engines in the 350 to 500 hp range.
As to the !000 hp engine losing 400 hp, that is too much of a loss. I would guess 150 to 200 hp loss tops.
There was a huge post on this about 9 months ago, I wish I could find it. We even had an aircraft Jet engine dyno engineer give us some ins and outs on the subject!
I look at it this way. Say the Z06 405 fwhp is correct. They dyno at about 350/355 rwhp stock. So the loss is about 13%. So you can divide by .87 to get and approximate fwhp figure from a rwhp figure.
The drive line loss is a % because of the increase loss of hp to friction and rotating mass as the gross hp increases. Think of it this way, as the hp goes to say 500 rwhp, the friction in the driveline DOES NOT stay the same! It goes up to! Those gears etc, are grinding together harder and getting hotter!
That is why the loss is a percentage. Whether the percentage stays at a constant 13% is another question, I doubt that it does. But that seems like a good figure for Vette engines in the 350 to 500 hp range.
As to the !000 hp engine losing 400 hp, that is too much of a loss. I would guess 150 to 200 hp loss tops.
Race Director
Joined: Apr 2003
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From: Tampa, Florida
Re: Drivetrain HP loss?? (CJS)
15% is a default value. Its a,"I dont know what drivetrain loss is so lets use 15%". Heres my rational. Over the years GM has added roller cams and rockers to the SBC. They do this to reduce internal friction which in turn yeilds better gas mileage and more power. Each engine/drivetrain combination has it own % of loss. From the post on stock C5 MN6 dyno results there is about a 13% loss for the C5. An average RWHP of 310ish/.87 equals 350hp.
The answer to your question, how much crank HP would a 1000 RWHP vette have is around 1200.
Does the drivetrain from an '85 vette have the same loss as a LS-6? No. Therefore they have a different % loss.
[Modified by jim2527, 9:48 AM 5/25/2003]
The answer to your question, how much crank HP would a 1000 RWHP vette have is around 1200.
Does the drivetrain from an '85 vette have the same loss as a LS-6? No. Therefore they have a different % loss.
[Modified by jim2527, 9:48 AM 5/25/2003]
Team Owner
Joined: Sep 1999
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From: Swansea IL
Re: Drivetrain HP loss?? (Horsepower)
A buddy who just did the NCM delivery asked the question to "a GM engineer" that was present, he stated a rough figure was 13% loss for the MN6 and 16% for the A4. But like anything every car/dyno will yield slightly different results.
I recall a challange Horsepower TV claimed last year about the value of replacing the trans/diff fluid in a manual trans car to pick up some HP. They had so many request that they did a segment on tv. They dyno'd a LS1 6-speed Z26 (remember their shop/dyno is all in doors which should eliminate weather variables and they tested one car on the same dyno maybe about an hour later) They picked up 9 RWHP by switching to Royal Purple, proving the value of lowering frictional losses. I'm going to be doing the same to my 99 since it'll be 5 years old this Nov and it's time for a complete fluid change anyway.
Tom
I recall a challange Horsepower TV claimed last year about the value of replacing the trans/diff fluid in a manual trans car to pick up some HP. They had so many request that they did a segment on tv. They dyno'd a LS1 6-speed Z26 (remember their shop/dyno is all in doors which should eliminate weather variables and they tested one car on the same dyno maybe about an hour later) They picked up 9 RWHP by switching to Royal Purple, proving the value of lowering frictional losses. I'm going to be doing the same to my 99 since it'll be 5 years old this Nov and it's time for a complete fluid change anyway.
Tom
