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post #1 of 8 (permalink) Old 02-04-2004, 02:03 PM Thread Starter
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hp loss

Just wondering what the percentage of horsepower loss from crank to the rear wheels???

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post #2 of 8 (permalink) Old 02-04-2004, 02:40 PM
 
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15-20%, but some will tell you your a moron if you use 20% "Cause our cars are 15% NO MATTER WHAT!" (long story)
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post #3 of 8 (permalink) Old 02-04-2004, 03:18 PM
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I don't really want to get into the details about this but it isn't a percentage. Let's just say that you have a certain amount of parasitic loss through the driveline, but that it doesn't matter how much power you have, the parasitic loss will be the same (relatively speaking). Well at least not until you get into a very high horsepower range (700+), then it becomes more like a percentage.

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post #4 of 8 (permalink) Old 02-04-2004, 03:47 PM
 
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to lessen those losses would u say a alum drivshaft... and anything else that would turn weather made outta alum or titanium... since in my mind they would be easier to turn correct?
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post #5 of 8 (permalink) Old 02-04-2004, 04:24 PM
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Yes lessening the weight of the rotating mass in the driveline will reduce the loss. Driveshaft, light weight gears (rearend and tranny- custom parts), and stall convertor (a smaller one is lighter).

Russell

JL's chassis braces, ST springs w/ 1 coil cut in rear (27.2" F 28" R), Airlift airbags (5 psi), Bilstein shocks, Cobra brakes F & R, ROH RT 17x9s, 255/285s Khumo Ecsta MX tires, 2.5" dual exhaust w/borla mufflers, 1 3/8 f & r bars, remote filter,subframe buildup, Al differential bushings, J-modded '02 tranny, 9.5" DD stall, 30K Hayden cooler, PI intake, 02 GT MAF, XCal 2

Want to talk/hangout with MN12 owners from GA? Go here.
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post #6 of 8 (permalink) Old 02-04-2004, 06:31 PM
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Whitebird and 96bird are both sorta right and technically wrong. It's not a definate percentage, but it's not a definate amount either. It's a complex equation dependant on more things than how much power your making.

Unless you have over 300rwhp, just use 20% for an AOD, 15% for a 4r70w, and 13% for a manual. Close enough for bench racing.




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post #7 of 8 (permalink) Old 02-04-2004, 07:16 PM
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OK. Here is some reading. I'm not saying that what I said is right, but I have heard both theories (percentage and static number) and this is as good an explaination as any. That is assuming you don't have access to the complex equation that GreenBird was talking about.

driveline loss

That is at the bottom of the page. I have heard this same thing many times.

Quote:
Nothing has changed between the flywheel and the rear wheels on our '93 LX, so does it make sense to figure the drivetrain is now absorbing nearly twice as much power? Such a concept just doesn't jibe in our little brains, so we asked a couple of people in the biz what they thought. Lee Bender of C&L Performance and Paul Svinicki of Paul's High Performance are both well versed in evaluating Mustangs on the dyno, and they both agreed that extrapolating drivertrain horsepower loss via percentages is flawed. Lee believes that the stick Mustangs experience roughly a 35hp loss through the drivetrain, whether they make 200 hp or 400 hp. He did explain that ultra-high-powered vehicles - typically race cars - can be and exception to this rule, but that's a topic for another time. Interestingly, a 35hp loss for stick-shifted drivetrains is strikingly similar to the difference between Ford's horsepower ratings and the rear-wheel numbers we've observed on dynos across the nation. Hmmm...

JL's chassis braces, ST springs w/ 1 coil cut in rear (27.2" F 28" R), Airlift airbags (5 psi), Bilstein shocks, Cobra brakes F & R, ROH RT 17x9s, 255/285s Khumo Ecsta MX tires, 2.5" dual exhaust w/borla mufflers, 1 3/8 f & r bars, remote filter,subframe buildup, Al differential bushings, J-modded '02 tranny, 9.5" DD stall, 30K Hayden cooler, PI intake, 02 GT MAF, XCal 2

Want to talk/hangout with MN12 owners from GA? Go here.
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post #8 of 8 (permalink) Old 02-04-2004, 08:17 PM
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Good link, I think all he managed to prove is that it can be "proven" either way.

Another thing to remember is that you lose almost as much in the rear end as the transmission. One mistake that comes of this is overstating the losses.

Not saying it's just a pecentage, but I'll use them to prove my point. Lets just say that: transmission losses are 9%, rear end losses are 8%. What's the driveline loss? 17%? Wrong. You lose 9% in the transmission, but you lose 8% of 91% in the rear end, making the losses 16.3%. Do this for every single part of the driveline and you start to get an idea of what the "complex equation" involves.




Matt "Looks Like Egon" Davis
96 Alpine Green V8
98 Audi A8 4.2Q in Racing Green Totalled
02 Audi A8L 4.2Q in Black

I buy my OEM Ford parts at 10% over dealer cost from Steve in White Bear Lake, MN.
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