Drivetrain loss?

[USMC0341]

when trying to figure out crank hp from rwhp, what do you use for drivetrain loss 5%, 10%, 15%??

thanks

 

[ModsAway]

I think its like 12-20% or so. Always a guestimation at best.

 

[piss&vinegar]

I always heard 17%

 

[LizardMan]

As I've posted twice in the last couple days: from Ford's 690 HP whipple project figures (690 FWHP = 601 RWHP), the correction factor is (0.871). Divide the RWHP by 0.871 to find FWHP.

Their project had a stock Cobra IRS (w/3.7 gears) and a stock Cobra trans. If Ford's numbers are believed they just gave us the real Cobra drivetrain loss figure: 12.9% of the FWHP.

I had my 04 base-line done today, only 352 SAE RWHP, but using the 12.9% loss figure that's still 403 SAE FWHP. Using a 15-17% loss figure would make the FWHP even higher, as would using the STD HP curve. I asked for SAE, as that's an honest modern standard curve matching what Ford and other use.

 

[Tom's_03SVT]

15-18% manual
20-22% auto

 

[CobraBob]

LizardMan, 12.9% seems too low. I have always used/heard 15-18% for the manual tranny like Tom posted above. I used 16%. I don't think you'll find an exact number that works for every car.

 

[LizardMan]

LizardMan, 12.9% seems too low. I have always used/heard 15-18% for the manual tranny like Tom posted above. I used 16%. I don't think you'll find an exact number that works for every car.

12.9% is lower than the rule of thumb figures everyone has been using, but it's at least based on hard numbers from a source that actually tested the engine at the flywheel and then again at the rear wheels. I haven't seen any other flywheel test numbers posted here. Plus, they used the stock trans and IRS.

Has anyone else pulled the motor, tested at the flywheel, reinstalled the motor and tested at the rear wheels?

 

[03DOHC]

Has anyone else pulled the motor, tested at the flywheel, reinstalled the motor and tested at the rear wheels?

Yes, someone did post about that before. Engine did something like ~425hp and in the car it did ~360rwhp. Been a while so I forgot who did it.

 

[CobraBob]

I guess you can use the 12.9% figure but that is just too low IMO. Unless you can prove the number in a real world setting (engine dyno vs. a chassis dyno) it is just a conversion guesstimate, which might be all you want.

 

[Fast Willy]

I've always used about 15 to 18%.