Converting WHP To Crank HP - Dodge SRT Forum

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#1 · Jan 22, 2008 (Edited by Moderator) Does anyone know the calculation on how to convert wheel horsepower to crank horsepower? I read that you have to take the WHP and divide it by 0.85, and you get the crank horsepower. Any truth to this or is there a different formula? Sort by Oldest first Oldest first Newest first Most reactions #2 · Jan 22, 2008 well their is alot of factors in this with axels and transmission wear and tear. I've always thought of it as 15% take away for est. crank HP #3 · Jan 22, 2008 15-18% for a manual trans, 18-21% for an auto. Autos have a little more parasitic loss than manuals do #4 · Jan 22, 2008 Point is, there is no formula. There are WAAAAAAY too many variables. Just guesstimate about 15-18% above WHP. #5 · Jan 22, 2008 FWD is about 15% Drivetrain loss so take whp/.85 = FWHP RWD is about 18% Drivetrain loss so take whp/.82 = FWHP AWD is about 20% Drivetrain loss so take whp/.80 = FWHP Those are the rough estimate numbers for converting flywheel hp to wheel hp for each type of car. Remember guestimates, not exact but it should be close. #6 · Jan 22, 2008 I think most FWD these days would be in the 12% range. transaxles have gotten MUCH more efficient over the years. But the combined tire/wheel/brakes weight plays a big part in power numbers as well. Like everyone else is saying, there's no straight number you can say unless you get YOUR engine on an engine dyno and see what it's putting out. #7 · Jan 22, 2008 Power to the ground is the only power that matters. #8 · Jan 23, 2008 :imwithstu 0 Reply #9 · Jan 23, 2008 Well I've always heard 10%-15% for a manual fwd. So I always go with 12% to be right in the middle. #10 · Jan 24, 2008 totally depends on the car, I have a 300m, and like all of the lh body cars, especially with 42le auto trannies, the loss is right at 30 percent, yes, thats thirty percent, we are talking brand new 180's whp, 253 crank hp. The lh sedans were orignially designed with the crank running front to rear so thehy could be built awd someday, which never happened, this design incorporated a transfer chain and sprockets since now the poewr had to go back forward to the half shafts through a differential (very heavy by the way). Anyway, the point is, depends entirely on the car, one rough way to do it, take a car perfectly stock, dyno it, compare it to the numbers the manufactuer puts out for engine horsepower, extrapolate the difference as a percentage and go with that, it wont ever be exact unless you use an engine dyno, but there it is. #11 · Jan 24, 2008 Take the SRT8s for instance. 425crank horsepower stuffed through an automatic trans nets 365whp. That's roughly 15%...every car is different. #12 · Jan 24, 2008 I agree.. too many variables and if there is a formula, it should be different for every car. For our SRT-4's, I keep hearing 15%, haven't seen the black and white to back it up though. Now, this may be my stupidity speaking, but I'm guessing if you up'd the HP in a car it would suffer less loss through the same drivetrain, i.e. the more power, the easier it would be to turn the same equipment. Just my way of thinking.. I mean take a 25lb. weight, who will exert more power lifting it, a built 250lb dude or a skinny 100lb chick? #13 · Jan 27, 2008 That might be true but technically if you no matter what get 15% drive train loss and you up the hp, technically the difference between crank hp and wheel hp grows bigger. 270 chp - 15% = 40.5 hp lost = 229.5 whp 380 chp - 15% = 57 hp lost = 323 whp 450 chp - 15% = 67.5 hp lost = 382.5 whp #14 · Jan 27, 2008 well "technically" the difference doesn't grow.. using your formula, whp will always be 15% of chp. But thats exactly the point I brought up.. at 270hp, you lost 40.5hp. To me, that's almost like saying it takes 40.5 hp just to get the drivetrain movin'. So, using the same drivetrain, why wouldn't it take the same 40.5hp to get it movin' at 380chp? why does it now take 57hp? shit, more hp, it should now be easier to get those tires turning.. using my example from earlier where the big dude(or engine) is lifting the 25lb. weight (or drivetrain), he may be exerting 15% of his energy (or HP).. now the skinny chick (smaller engine) lifting the same weight (or drivetrain) may have to exert herself 50% to lift the weight. that's my logic anyways..why is it 15% regardless of CHP? 0 Reply #15 · Jan 27, 2008 I understand what you are saying, and unfortunately I don't possess the knowledge to give you a good answer, so I am not going to try and bullshit you one. Hopefully one of the other guys might be able to. Oh and sorry, I didn't mean the percentage grows between crank and wheel hp, just that the numbers get bigger due to the total being larger. You got the point though I think I was badly making though. LOL #16 · Jan 30, 2008 I was always told 15% as well. This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread. Insert Quotes Post Reply

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