drivetrain power loss?
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,022
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From: CT
Re: drivetrain power loss? (Ryan77)
Thanks, so does that mean since i have around 380hp at the flywheel i should have 320 @ the wheels? (380 X .85 = 323)
That number seems higher then I expected.
That number seems higher then I expected.
Melting Slicks
Joined: Nov 2001
Posts: 2,659
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From: Katy (Houston) TX
CI 7-8 Veteran
Re: drivetrain power loss? (L-82kid)
Well these are very rough numbers. Also depends on things like what accessories you have, do you have a mechanical fan, type of exhaust, condition of all parts (tranny, rear end, etc). But I think a rough number to start from for a manual C3 is about 20%.
Le Mans Master
Joined: Oct 2000
Posts: 8,897
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From: Santa Ana CA
Re: drivetrain power loss? (L-82kid)
From dyno testing a couple weeks ago.
Dyno testing people said the most power measured out of a new stock, 405 hp Z06 was 350 at the wheels. This represents a lost of about 14%, so 15% is pretty good for late models. But isn't the late model with tranaxle a little more efficient than a separate trans/rear end?
ZZ3 and ZZ4 people were measuring about 225-250 hp at the wheels and these are rated at 355 hp/405 ft-lb. So at 250 at the wheels, your looking at about a 30% loss.
BTW, my 4-speed, '64, 331 CI (not stock but fairly mild) did 293 hp and 293 ft-lb at the wheels.
[Modified by toddalin, 11:16 AM 12/5/2003]
Dyno testing people said the most power measured out of a new stock, 405 hp Z06 was 350 at the wheels. This represents a lost of about 14%, so 15% is pretty good for late models. But isn't the late model with tranaxle a little more efficient than a separate trans/rear end?
ZZ3 and ZZ4 people were measuring about 225-250 hp at the wheels and these are rated at 355 hp/405 ft-lb. So at 250 at the wheels, your looking at about a 30% loss.
BTW, my 4-speed, '64, 331 CI (not stock but fairly mild) did 293 hp and 293 ft-lb at the wheels.
[Modified by toddalin, 11:16 AM 12/5/2003]
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Safety Car
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From: St Louis MO
Re: drivetrain power loss? (L-82kid)
Working with the 15% loss:
If I dyno my car and it has 350 rwhp, that means it has 412 hp (350 / .85) at the crank with a drivetrain loss of 62 hp. Right?
What if I change out the engine and use the same tranny and diff and get 425 rwhp? Does that mean I have 500 crank hp (425 / .85)? or does it mean that my tranny and diff still take 62 hp to turn and I have 487 crank hp?
Brett :thumbs:
If I dyno my car and it has 350 rwhp, that means it has 412 hp (350 / .85) at the crank with a drivetrain loss of 62 hp. Right?
What if I change out the engine and use the same tranny and diff and get 425 rwhp? Does that mean I have 500 crank hp (425 / .85)? or does it mean that my tranny and diff still take 62 hp to turn and I have 487 crank hp?
Brett :thumbs:
Team Owner
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From: Republic of Texas
Re: drivetrain power loss? (Ryan77)
I think the stick cars are about 15%
Team Owner
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From: Lakeland, FL
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St. Jude Donor '03, '06, '17
Re: drivetrain power loss? (L-82kid)
The 15% MT and 20% loss for AT is pure theory and is only applicable for cars with a modern drivetrain - using lightweight shafts and synthetic fluids etc...
A C3 typically loses 20 - 25% with MT and 30 - 35% with AT (TH350 = 30%, TH400 = 35%)..
A C3 typically loses 20 - 25% with MT and 30 - 35% with AT (TH350 = 30%, TH400 = 35%)..
Drifting
Joined: Feb 2002
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From: Berlin
Re: drivetrain power loss? (L-82kid)
Most answers to this topic are meaningless. Think about how the numbers that people throw around all the time. How were they found? There is no good standardized way of running a chassis dyno. When you buy a car, the phrase SAE net hp means something precise (assuming that the manufacturer actually followed the procedures). RWHP does not mean anything remotely precise. If it did, things like lightweight driveshafts wouldn't do anything for example (this is obvious). As others have said, numbers between 15-25% are average, but this should be taken with a very large grain of salt. If you use a dyno that's of an unusual design, or has an operator who does something out of the ordinary (I don't mean he's necessarily wrong), your numbers will be very different.
See this for example: http://www.sdsefi.com/techdyno.htm
See this for example: http://www.sdsefi.com/techdyno.htm
Race Director
Joined: Sep 1999
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From: Plano TX
Re: drivetrain power loss? (aharte)
As a rule of thumb you can use 20% for a stick C3. But this is a very rough estimate.
I saw a test once where they had a dyno chart for an engine and then rear wheels. Engine was identical between the engine dyno and as installed (same exhaust, accessories etc). The loss, as measured in percent, varied at different rpms. I saw losses as low as 9% and as high as 16%. This was a trans-am race car (tube chassis, best of everything).
I saw a test once where they had a dyno chart for an engine and then rear wheels. Engine was identical between the engine dyno and as installed (same exhaust, accessories etc). The loss, as measured in percent, varied at different rpms. I saw losses as low as 9% and as high as 16%. This was a trans-am race car (tube chassis, best of everything).
Safety Car
Joined: Feb 1999
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From: Fountain Hills AZ
Re: drivetrain power loss? (zwede)
The percentage of loss also depends on if you're comparing net fw hp or gross fw hp to rear wheel hp. Obviously, a net rated engine will see a lower percentage of loss, as measured at the rear wheels, than will a gross rated engine. An example of this is the ZZ4 which is rated at 355 gross (when set up as the test engine) and a 350hp net rated LS1. Guys with ZZ4's are reporting 230-280 rwhp depending on their set up while LS1 owners are reporting 280-310 rwp.
Le Mans Master
Joined: Oct 2000
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From: Santa Ana CA
Re: drivetrain power loss? (toddalin)
"ZZ3 and ZZ4 people were measuring about 325-350 hp at the wheels and these are rated at 355 hp/405 ft-lb. So at 250 at the wheels, your looking at about a 30% loss."
OOOPPPSSSS! sorry, a typo. :crazy: Should have read "225-250" hp at the wheels.
OOOPPPSSSS! sorry, a typo. :crazy: Should have read "225-250" hp at the wheels.
Burning Brakes
Joined: Jul 2000
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From: melbourne,Australia
Re: drivetrain power loss? (toddalin)
My 74 383 with 700r4 and 3.08 diff was on the chassis dyno a few weeks ago and ran to 339rwhp......the owner of the dyno shop and the specialist engineer/tuner who built the engine were adamant that for this combo i was losing 30 from the flywheel....guess that means i have 484hp at the flywheel....feels good to me...john :chevy
