Homer Posted July 18, 2005 Share Posted July 18, 2005 hehe, I love maths Sorry Slick but Jake's got it right, I would explain but think Jake can do it better Quote Link to comment Share on other sites More sharing options...
slick Posted July 18, 2005 Share Posted July 18, 2005 No he hasn't, as I just clearly explained. You cannot start the calculation with the figure that the calculation itself is supposed to work out. Take Thor for example, they don't give Flywheel figure estimates.... so how you gona calculate then eh? Hmmmmmm! Exactly, you start from the wheels/hub figure that the Dyno actually gives you like I've just said. So if Thor told you its 220 at the hubs and you wanted to use a 25% loss you would have to take 220 and ADD on 25% to reach 275 because there would be no mention of the 275 till that point, as you would only have the WHEELS (or hubs in Thors case) figure to work from with no mention of a Flywheel figure. If you can't understand that simple logic then I really do give up lol Quote Link to comment Share on other sites More sharing options...
mr keef Posted July 18, 2005 Share Posted July 18, 2005 So ive basically paid £30 for nothing? All the other readings were acurate though. What gives? mate i wish all rolling roads charged £30,as now some tuners just take the piss outa you,bend you over,shaft you,then give ya both barrels,and there rolling roads still can be way out. dont worry about it dude. Quote Link to comment Share on other sites More sharing options...
Digsy Posted July 18, 2005 Share Posted July 18, 2005 No he hasn't, as I just clearly explained. You cannot start the calculation with the figure that the calculation itself is supposed to work out. Bloody hell. Engines lose N% of their power output through the drivetrain. Just because you don't know what your flywheel hp is when your car goes on the rollers doesn't mean you can't work it out. You can re-arrange formulae, you know. I think we are all agreed that: rwhp = fwhp x (100% - loss%) But of course we don't know fwhp yet, so you rearrange the formula to make rwhp (which we do know) a variable, rather than the subject. fwhp = rwhp / (100% - loss%) So if loss% = 25% and rwph = 220hp, then: fwhp = 220 / (100% - 25%) = 200 / 0.75 = 293.33hp Jake is correct. Quote Link to comment Share on other sites More sharing options...
slick Posted July 18, 2005 Share Posted July 18, 2005 And 220 + 25% = what then (leaving your brackets at home)? Quote Link to comment Share on other sites More sharing options...
Digsy Posted July 18, 2005 Share Posted July 18, 2005 And 220 + 25% = what then (leaving your brackets at home)? 220 + 25% = 125% of the rwhp, which is not what you are trying to work out. You are trying to work out what you have to take 25% off of to end up with 220. And it isn't 275. 25% of 275 = 68.75 275 - 68.75 = 206.25 I can see where you are coming from: You can't subtract 25% of something you don't know, which is why you have to write the formula in a way that can be rearranged so that you can plug in the figures you do know. Seriously, I'm not trying to be clever or arsey or anything, but Jake is right on this one. Quote Link to comment Share on other sites More sharing options...
slick Posted July 18, 2005 Share Posted July 18, 2005 Hell I've changed my mind, I'm gona use your figures LOL it says mines got 467bhp that'll do me down the pub Quote Link to comment Share on other sites More sharing options...
mr keef Posted July 18, 2005 Share Posted July 18, 2005 ur all mad Quote Link to comment Share on other sites More sharing options...
slick Posted July 18, 2005 Share Posted July 18, 2005 You are trying to work out what you have to take 25% off of to end up with 220 I understand your workings out, thats fair enough... but surely when you have the wheels figure in front of you - such as my Thor example - your trying to work upwards from that point to get to a flywheel figure so you can just add on your percentage loss figure etc. I took it that more complicated formulae is used and required for times where you only have a Flywheel figure present and so you NEED to work back to the wheels figure and therefore it requires a more technical formulae as you've shown. Do you not agree with this at all? Quote Link to comment Share on other sites More sharing options...
Digsy Posted July 18, 2005 Share Posted July 18, 2005 I understand your workings out, thats fair enough... but surely when you have the wheels figure in front of you - such as my Thor example - your trying to work upwards from that point to get to a flywheel figure so you can just add on your percentage loss figure etc. I took it that more complicated formulae is used and required for times where you only have a Flywheel figure present and so you NEED to work back to the wheels figure and therefore it requires a more technical formulae as you've shown. Do you not agree with this at all?It's actually exactly the other way around to what you described above. You can simply add and subtract a % of you can reduce the % to a real number, so if you know the fwhp and the % loss then you can say "fwhp = 300 and 25% of the fwhp = 75hp so rwhp must be 300 minus 75: 225hp. That'll be £30 please, mate :)" But the drivetrain losses are a % of the fwhp, so you can't simply add it to the rwhp. To make sense, the calc would have to work in both directions: Let's assume you know your fwhp is 300hp and your losses are 25% 25% of 300 = 75, so rwhp = 300 - 75 = 225 Now assume the same car is on the rollers and you don't know the fwhp, but you know the rwhp is 225 and you guess the losses at 25%: 25% of 225 = 56.25, so rwhp = 56.25 + 225 = 281.25 ...which doesn't get you back to 300fwhp. At the risk of sounding condescending (which I don't want to do) think of it like your paypacket. The tax you pay is a % of your gross salary, not the net. The taxman subtracts 25% of your gross pay to get your net, but when you get tax relief on something you get back 33.3% of your net salary. If you got back 25% of your net pay you would be pretty hacked off Now, using the same figures and going back to the rollers: 33.3% of 225 = 75, so rwhp = 75 + 225 = 300 And now it all works. Quote Link to comment Share on other sites More sharing options...
letmeshowyou Posted July 18, 2005 Share Posted July 18, 2005 Ceptik, I think you've just been unlucky on this occassion. I know alot of people that use engine advantages, and I've never seen readings as odd looking as yours! My old NA one was rr'd there and I think scoboblio had his done there too at one point. Quote Link to comment Share on other sites More sharing options...
mikeyh Posted July 18, 2005 Share Posted July 18, 2005 mine is booked in at engine advantages on thursday bit worried about this now engine advantages has a very good reputation down here dont understand how it can be that far out Quote Link to comment Share on other sites More sharing options...
slick Posted July 18, 2005 Share Posted July 18, 2005 Thats an excellent explanation Digsy, thankyou. I've never seen it put down all together like that before so clearly.... it should be in the FAQ's if it isn't already. I know a lot use a similar formulae such as using .85 for RWD and .90 for FWD etc as shown on Puma racing and WRC etc.. but never seen it laid out as clearly. I don't mind appologising for getting that wrong, as its been a good lesson. I can see looking at it all laid out there that a simple addition of a percentage is no good when working both ways and ofcourse with the nature of RR figures thats important. Sometimes it pays to go beyond surface logic eh? Can I say a big Doh! Think the Puma formulae might be a bit more realistic though as 0.75 seems a bit high although it'd be great if it was right They say rwhp +10 / .88 Quote Link to comment Share on other sites More sharing options...
Gordon F Posted July 18, 2005 Share Posted July 18, 2005 What we really need is for someone to pluck their engine out and run it on an engine dyno to measure true fwhp. Then, slip it back into the car and take it off to a trusted r/r to measure the true rwhp. Should be able to work out the real transmission losses from there. Losses are likely to vary from car to car, but hopefully not too much. Then repeat the process for an auto / manual depending on which was done first. My totally stock auto made 249 rwhp on the rollers which seemed about right to me. Quote Link to comment Share on other sites More sharing options...
Jake Posted July 18, 2005 Share Posted July 18, 2005 Awwww, I missed all the fun! I didn't realise there had been any replies let alone such heated ones! Anyway, I'm glad to see it's all been sorted out and Slick's now happy. If it's any consolation Slick mate, I had exactly the same trouble getting my head round it at first. to Darren for having the patience to type it all out like that. I would have given up halfway though. Quote Link to comment Share on other sites More sharing options...
slick Posted July 18, 2005 Share Posted July 18, 2005 to Darren for having the patience to type it all out like that. I would have given up halfway though. He did a good job didn't he. Apologies Jake, its definately one of those things that unless you've really looked into it (as you chaps obviously have) then it can appear superficially simple... esp to a stubborn, bad tempered numbskull like me with a big fat foot fixed firmly in my mouth half the time Quote Link to comment Share on other sites More sharing options...
Jake Posted July 18, 2005 Share Posted July 18, 2005 No probs mate, we've all done it. Quote Link to comment Share on other sites More sharing options...
Ceptik Posted July 19, 2005 Author Share Posted July 19, 2005 Just got back to this. Looks like i started a mini world war 4 there. Whoops! Quote Link to comment Share on other sites More sharing options...
Digsy Posted July 19, 2005 Share Posted July 19, 2005 World War 4? I guessed that WW3 might be over quicky, but wow - I didn't even notice it Anyway - here's a handy conversion table that lets you start from either rwhp or fwhp and work backwards or forwards by doing simple addition or subtraction. Select your chosen transmission losses % from the first column, and if you are working back from rwhp, add the % in the second column. Quote Link to comment Share on other sites More sharing options...
Ceptik Posted July 19, 2005 Author Share Posted July 19, 2005 Clever stuuf, thanks Digsy. On a different note, what is the animation about in your avatar? Its quite scary! Quote Link to comment Share on other sites More sharing options...
Digsy Posted July 19, 2005 Share Posted July 19, 2005 Its a clip from the vomiting scene from Team America Quote Link to comment Share on other sites More sharing options...
JohnA Posted July 19, 2005 Share Posted July 19, 2005 classy, yet not quite appetising Quote Link to comment Share on other sites More sharing options...
Ceptik Posted July 19, 2005 Author Share Posted July 19, 2005 mmmmm, nice. Need to see that film! Quote Link to comment Share on other sites More sharing options...
tbourner Posted July 19, 2005 Share Posted July 19, 2005 Does anyone have any idea on the differences between hub hp and wheel hp? I'm sure someone on here said the RWHP tranny losses would be 16% ish on a TT6, but RHHP would be more like 9%!!! That's no good for my massive pub figure I got from Thor!!! Surely tyres don't make that much of a difference? Quote Link to comment Share on other sites More sharing options...
Bobbeh Posted July 19, 2005 Share Posted July 19, 2005 18% percent loss on a manual on a rolling road for RWHP, 25% for autos Hub dynos... god knows.. something like 9-11% I'd imagine. (for a manual anyway) Quote Link to comment Share on other sites More sharing options...
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