turkey Member 9 Member For: 18y 10m 25d Posted 12/07/05 02:17 AM Share Posted 12/07/05 02:17 AM Hi guys I was just wondering if anyone could tell me how to calculate rwkw to flywheel kw. I recently Put my stock xr6t on the dyno it is an auto. It made 202.3rwkw im just curious to see what that is at the flywheel. Link to comment Share on other sites More sharing options...
Power The 'nice guy' Donating Members 314 Member For: 19y 22d Gender: Male Location: Sydney (Area around Ryde) Posted 12/07/05 02:35 AM Share Posted 12/07/05 02:35 AM Every car seems to vary widely as do some dynos.You mentioned you have an auto (like me) at 202.3rwkw. So does this mean you have 240fwkw with 84.3% getting to the treads? That would also be one hell of a stock auto, if not the best ever?!Mine auto was 185.9 STOCK (good for an auto), so am I getting only 77.45% to the treads based on the Ford spec? If so, my current 279.8rwkw is around 361fwkw, which I doubt just a little.I've given up guessing as it will slowly drive you mad. :uziman: If you search there are endless threads on this.... 1 Link to comment Share on other sites More sharing options...
Geeseman Donating Members 1,805 Member For: 20y 5m 29d Location: Sydney Posted 12/07/05 03:07 AM Share Posted 12/07/05 03:07 AM Add about 25% of the power to get your figure (X 1.25) so you'd be about 252rwkw but that's only an assumption.Although stock cars do see to differ in power, I think alot of it is down the the computers differing maps for each car. Ive seen some run 4psi and others up near 6, which explains some of the power variations. As soon as you mod the car it tends to level out, but no doubt there are some variances between build quality that's for sure. 1 Link to comment Share on other sites More sharing options...
cobrav8 Member 1,969 Member For: 19y 1m 1d Gender: Male Location: New Zealand Posted 12/07/05 03:43 AM Share Posted 12/07/05 03:43 AM There is no hard and fast formula - every tyre/universal joint/diff/driveshaft/gearbox/clutch combination swallows different amounts.It is also not a percentage - as if you run a higher horsepower motor through the same setup you should not lose as much in percentage terms as the first loss is from having to drive the gears etc - ie you will lose what you did on the standard motor and some more from additional friction - but not the same percentage as before. Link to comment Share on other sites More sharing options...
turkey Member 9 Member For: 18y 10m 25d Posted 12/07/05 03:48 AM Author Share Posted 12/07/05 03:48 AM Thanks for the help guys Link to comment Share on other sites More sharing options...
Flukey Seriously Flukey Member Donating Members 4,354 Member For: 20y 1m 4d Gender: Male Location: Melbourne Posted 12/07/05 03:54 AM Share Posted 12/07/05 03:54 AM Assuming the driveline losses for a manual are 17% and 23% for an auto, you should multiply your rwkw by 1.2 for a manual and 1.3 for an auto These should be close. Link to comment Share on other sites More sharing options...
Lawsy Wanabe mechanical engineer Donating Members 960 Member For: 19y 7m 8d Gender: Male Location: At the computer, obviously..... Posted 12/07/05 04:03 AM Share Posted 12/07/05 04:03 AM I reckon I got a bit of a theory on this one....Its always bugged me why the losses are so inconcistant from car to car, of varying power levels.... It also got me thinking, why is it that some of the higher powered cars seem to have less transmission losses? (ie, 500+kw cars that have been chassis and engine dyno'd showing what seems to be overall, only about 18% or so).Well, I thought to myself "That can't be right!"So anyways, it goes something like this.Power is the work done, right? So its a form of energy...You can have kenetic, thermal and potential/chemical energy.This got me thinking "It can't be a simple percentage on a per gearbox basis, it just doesn't work! There must be a constant loss, then a loss due to friction (heat)... "Well, a gearbox has an inertial mass (the gears in the box.... )........It takes energy to get these components moving and to keep them moving. This loss would have to be fairly constant as the weight doesn't change. This also includes drive shafts, axils and the diff. So all of these losses that are caused by the mass being moved all stay the same...Then, there the friction between all these weights in the gearbox, friction from moving the oil around, friction in the pumps, in the diff, bearings, etc.As a rule of thumb, the more pressure you apply to any 2 surfaces that have friction between them, the greater the friction is going to be... And the more energy required.This would not be constant though, infact this would probably be some form of the mechanical heat equation (which is ever so slightly exponential). But who cares, we'll just make it consistant for this...So there is always going to be a constant lose of about, say, 20kw in trying to overcome all the inertial masses in an automatic (probably 5 - 10kw less in a manual) and then a percentage loss after that due to the friction between the components.... Lets have a stab and make it, say, 16%....You'll probably find this is allot closer to reality than just going "oh, its 25% - 30%" that most people dish out....So, does it work? Well, sortof.240 - (240(16/100)) = 201201 - 20 = 181... That seems to be close to the norm for an auto, don't you think?This would mean that the large variances we see in engines are either the dyno's fault, or has something to do with the friction percentage. The mass of the entire drivetrain is pretty much the same every time...With a manual, it would probably be more like 15kw and 14% loss or something...Which would be 191kw... Again, fairly normal, for a manual.So it is fairly close here and seems to be ALOT more accurate when talking with big engines...So yeah, that's my theory... Feel free to prove me wrong, correct or maybe even agree! I really don't mind either way because it gave me something to do for the last 10 minutes that would have otherwise been work related. Link to comment Share on other sites More sharing options...
cobrav8 Member 1,969 Member For: 19y 1m 1d Gender: Male Location: New Zealand Posted 12/07/05 04:05 AM Share Posted 12/07/05 04:05 AM I think we are on the same wavelength Lawsy - you just used more words (in fact I think you used them all in that post!) Link to comment Share on other sites More sharing options...
Lawsy Wanabe mechanical engineer Donating Members 960 Member For: 19y 7m 8d Gender: Male Location: At the computer, obviously..... Posted 12/07/05 04:08 AM Share Posted 12/07/05 04:08 AM I think we are on the same wavelength Lawsy - you just used more words (in fact I think you used them all in that post!)LOL, yeah, I didn't see your post, you must have posted the instant I started my reply... Link to comment Share on other sites More sharing options...
Blown BA In Your Face Member 6,195 Member For: 21y 1m 16d Gender: Male Location: Peninsula Posted 12/07/05 06:05 AM Share Posted 12/07/05 06:05 AM I think we are on the same wavelength Lawsy - you just used more words (in fact I think you used them all in that post!)<{POST_SNAPBACK}>Yeh the Nutty Professor has struck again Link to comment Share on other sites More sharing options...
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