Ebized Posted August 12, 2011 Share Posted August 12, 2011 Usually its somewhere between 15-17% quoted - but I never get this percentage thing as if you have 500HP, you're not going to lose more than someone running a stock engine if you have the same running gear Saying that as Captain has an auto it will lose a bit more, so I'd say hes just tipping over 300HP Going by 17%, that gives my 370z 360+HP (and more likely as I have an auto too) Same for me and makes the lbft torque a shade over 300 at the fly whereas it is about 260 at the hubs and I see from the dyno thread the two are variously quoted, which of course can distort perceptions. Mark @ Abbey certainly shys away from set percentage calcs between the fly and hubs as there are a host of variables - i.e. see here: http://www.rndengineering.co.uk/page_p1 ... horsepower Quote Link to comment Share on other sites More sharing options...
Wasso Posted August 12, 2011 Share Posted August 12, 2011 +1 with Colin - don't use a percentage figure, I did and it's not accurate in the slightest. There are certain variables. Maybe Mark @ Abbey could explain in full the dynamics of ascertaining FWHP. I was told +30 from whatever hhp you achieve. But then if you look at Tony420z, if he's pull 1khhp, what would the fwhp be?? 1,030fwhp?? I'm not confident on that. Quote Link to comment Share on other sites More sharing options...
docwra Posted August 12, 2011 Share Posted August 12, 2011 Of course the losses are a percentage, the percenbtage just differs from car to car (and roller to roller). Coming from FI cars, those curves are about as sexual as the ones on Kelly Brook. 220 odd lb/ft @ 2000 RPM?? Im going to see Jeremy next month I think, has to be done. Quote Link to comment Share on other sites More sharing options...
Jez @ H-Dev Posted August 12, 2011 Share Posted August 12, 2011 Good to meet you Bry - glad you're pleased with the results Docwra - hope to see you soon. Quote Link to comment Share on other sites More sharing options...
Chris`I Posted August 12, 2011 Share Posted August 12, 2011 Of course the losses are a percentage, the percenbtage just differs from car to car (and roller to roller). While it can be expressed as a percentage, I fail to see how the drivetrain losses are anything other than an absolute loss. How can having more power cause you to use more to move the same drivetrain? If before my car is remaped it loses 30HP in drivetrain losses, surely its going to have 30HP losses after the remap. If you express that as a percentage, you are saying the more power I have the more I lose in the drivetrain. The reason 15-17% is bounded about is because its easy for dyno operators to guess the numbers using it to give a good flywheel estimate. Hence why its largely known as a "fudge factor" Quote Link to comment Share on other sites More sharing options...
Jez @ H-Dev Posted August 12, 2011 Share Posted August 12, 2011 Dyno losses aren't simple. You have a few things that sap energy from the hubs and tyres: Gearbox Prop shaft Diff Drive shafts Tyres The prop shaft and drive shafts absorb pretty much no energy - theres only the joints that have low friction and low energy absorbtion. The gearbox absorbs some engery - mainly through oil churning (which would be a loss mainly based on rpm - i.e. as rpm rises so does the energy absorbed, but load increase doesn't make much difference) and some friction (this would be a small loss that increases with load and rpm) Tyres absorb a fair amount of energy - the amount they absorb would rise with rpm and load. Mainly because the faster the tyre turns on the roller the more energy they turn to heat and the more load you have the more they'll deform and turn energy to heat. So, having a fixed percentage loss for hubs / wheel figure is pretty meaningless unless you're talking about very similar conditions (roughly the same power output, wheel speed, engine rpm etc etc) If you assumed a 15% loss on a 1000bhp engine you'd be dumping 150bhp of energy into the drive train - it'd get so hot things would melt - 150bhp is about 100kw. Thats about 40 kettles worth of energy heating things up. And another thing - the whole 4wd cars lose loads of power through the drive train. Well, they'd lose a little bit more but the main loss is through the tyres. And with a 2wd car on a 2wd dyno you're only turning 2 wheels. In real life you'd have losses from all 4 wheels, driven or not. The difference is that a 4wd car has all four tyres absorbing energy from the measured power figures, 2wd drive cars on a dyno are only losing power from 2 wheels. Quote Link to comment Share on other sites More sharing options...
Chee350 Posted August 17, 2011 Share Posted August 17, 2011 Bry they're some good gains! Im going to be starting my Z soon hopefully in the next month so il be looking at doing the same style of mods that you've carried out before my remap that I may now well get Jez to do. I am however interested in the Buddy Club exhaust you have fitted. hows life with it? I was looking at them but have read their extremely loud even at low revs. is this the case? cheers and jelous of the mods Quote Link to comment Share on other sites More sharing options...
Bry Posted August 17, 2011 Author Share Posted August 17, 2011 It's very loud and I would only recommend it if your car is a wekend toy not a daily driver. Everybody that has heard it loves it Quote Link to comment Share on other sites More sharing options...
Iwantone Posted August 18, 2011 Share Posted August 18, 2011 Maybe I'm missing something here, but what is the interest in the power available at the flywheel? Surely its an academic figure, it must be what's available at the driving hubs that's interesting. Steve Quote Link to comment Share on other sites More sharing options...
Bry Posted August 18, 2011 Author Share Posted August 18, 2011 Maybe I'm missing something here, but what is the interest in the power available at the flywheel? Surely its an academic figure, it must be what's available at the driving hubs that's interesting. Steve You're right you are missing something as I've also quoted the WHP figure Quote Link to comment Share on other sites More sharing options...
Iwantone Posted August 18, 2011 Share Posted August 18, 2011 Maybe I'm missing something here, but what is the interest in the power available at the flywheel? Surely its an academic figure, it must be what's available at the driving hubs that's interesting. Steve You're right you are missing something as I've also quoted the WHP figure I've not suggested that you have not quoted the WHP number. What I've questioned is the significance of the BHP figure at the flywheel 'cos I'm failing to see it. Its a genuine call for enlightenment. Steve Quote Link to comment Share on other sites More sharing options...
Bry Posted August 18, 2011 Author Share Posted August 18, 2011 It's just a reference point, WHP is the more important figure but most people rightly or wrongly are more familiar with the flywheel figure. Quote Link to comment Share on other sites More sharing options...
Chris`I Posted August 18, 2011 Share Posted August 18, 2011 What I've questioned is the significance of the BHP figure at the flywheel 'cos I'm failing to see it. Its a genuine call for enlightenment. Steve Because its what OEMs quote and its the number people want to know. I.e. I have a 370z - it comes from the factory with a quoted power of ~330HP. I got it dyno'd after fitting exhaust, intakes and having UpRev. I get 308HP@hubs. How do I compare that to the OEM figure? You cant - you can only use flywheel. In my case its ~360HP which is a nice 30HP bump Quote Link to comment Share on other sites More sharing options...
Wasso Posted August 18, 2011 Share Posted August 18, 2011 What I've questioned is the significance of the BHP figure at the flywheel 'cos I'm failing to see it. Its a genuine call for enlightenment. Steve Because its what OEMs quote and its the number people want to know. I.e. I have a 370z - it comes from the factory with a quoted power of ~330HP. I got it dyno'd after fitting exhaust, intakes and having UpRev. I get 308HP@hubs. How do I compare that to the OEM figure? You cant - you can only use flywheel. In my case its ~360HP which is a nice 30HP bump So you are losing 52horses through the drivetrain, surely not! That's a big number, that's more than 10% Quote Link to comment Share on other sites More sharing options...
Chris`I Posted August 18, 2011 Share Posted August 18, 2011 Normally drivetrain losses are quoted at 15-17% which gives somewhere between 355-360HP. Always nice to over egg it given its an auto If you say its ~30HP loss then that only gives me 338HP which means I've gained 8HP over stock which isnt right. Say 40HP for an auto, gives 348HP, which is probably more likely. Need to get it on a DynoDynamics and see what that decides it is. Quote Link to comment Share on other sites More sharing options...
Wasso Posted August 18, 2011 Share Posted August 18, 2011 Chris didn't the percentage rule get discussed, it can't be used as a rule. I've had a further read on the web and there's a lot to dismiss the rule of percentage. What REALLY MATTERS is the WHP or HHP, improvements to your vehicle via modifications will result in what happens with contact with the road. So in all fairness, we should ALL forget FWHP and start all noting what we ACTUALLY dyno at. That's what matters to us all. Quote Link to comment Share on other sites More sharing options...
Chris`I Posted August 18, 2011 Share Posted August 18, 2011 So in all fairness, we should ALL forget FWHP and start all noting what we ACTUALLY dyno at. That's what matters to us all. This is true, but while OEMs quote flywheel figures people will strive to "guess" what theirs is compared to the OEM figure. This is why DynoDynamics seem to always give you figures quoted at the fly - and more savvy members request at the wheel. I didnt have mine dyno'd before I started fitting mods so we had no way of knowing what it was compared to stock. Mark had a stock car in which dyno'd at 275@hubs (293 with drop-in filters, exhuast and UpRev), mine dyno'd at 303 with exhaust and intakes, it gained a further 5HP with UpRev (quite a bit more low down grunt though). So make of all that what you will Quote Link to comment Share on other sites More sharing options...
Iwantone Posted August 18, 2011 Share Posted August 18, 2011 Chris didn't the percentage rule get discussed, it can't be used as a rule. I've had a further read on the web and there's a lot to dismiss the rule of percentage. What REALLY MATTERS is the WHP or HHP, improvements to your vehicle via modifications will result in what happens with contact with the road. So in all fairness, we should ALL forget FWHP and start all noting what we ACTUALLY dyno at. That's what matters to us all. Well said, Wasso, and my point exactly. I'm an engineer and have a need to be able to accurately measure things. When I read this thread and realised that there was a BHP figure that could be accurately measured and plotted (wheels) I failed to realise why anybody would have any interest in a predicted figure. I didn't know at that point that the manufacturers quote the flywheel figure in their advertising bumpf, etc. They are, of course, able to accurately measure the flywheel figure on bench testing rigs. I wonder if they remove the drive belt from the alternator, water pump, etc, to get the BHP figure even higher? My advice (and I don't give much) is to get your car dyno plotted before and after any changes to determine the difference (if any) made by the changes. They are the only meaningful figures that you have. Steve Quote Link to comment Share on other sites More sharing options...
Bry Posted August 18, 2011 Author Share Posted August 18, 2011 Mine made 282bhp (fly) before uprev and 300bhp after. Personally I want as much information from a Dyno run as possible so FWHP, WHP,HHP are all of interest to me. Quote Link to comment Share on other sites More sharing options...
Wasso Posted August 18, 2011 Share Posted August 18, 2011 So in all fairness, we should ALL forget FWHP and start all noting what we ACTUALLY dyno at. That's what matters to us all. This is true, but while OEMs quote flywheel figures people will strive to "guess" what theirs is compared to the OEM figure. Agreed, but why aim for a number which is incorrect? I found a site not long ago, they dyno every new car that is manufactured. They dyno then compare against manufacturing figures. The Zed is claimed to lose 10% from manufactured figures even before it's driven 1 inch! I looked up the Leon Cupra K1 - as a friend has one, they lose 5% from manufactured figures. Although we all love the fact of achieving the highest number, FWHP can only be measured on a bench as mentioned by Iwantone.... We can all try and guess our FWHP but why use a guestimation? I like the fact I have a plotted dyno which tells me the truth. Dynodynamics dyno's showing FWHP are technically missleading. We should also take into account the age and the condition of the vehicle, these could also contribute to powertrain loss. Quote Link to comment Share on other sites More sharing options...
Chris`I Posted August 18, 2011 Share Posted August 18, 2011 Fully agree chaps, thats why I quote hub figures in my sig and garage This is why we need dyno shootouts so we can all dyno together Quote Link to comment Share on other sites More sharing options...
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