Digsy Posted November 12, 2012 Share Posted November 12, 2012 It should be 540.4 at the flywheel if the autobox loss is 22% About 540fwhp given the estimate transmission losses mate I'm afraid you're both wrong. Its 568fwhp. The 22% is calculated from the fwhp, not the rwhp. The rwhp is the 78% that is left, so the correct maths is: fwhp = rwhp x 1/0.78 Quote Link to comment Share on other sites More sharing options...
Chris Bailey Posted November 12, 2012 Share Posted November 12, 2012 I'm afraid you're both wrong. Its 568fwhp. The 22% is calculated from the fwhp, not the rwhp. The rwhp is the 78% that is left, so the correct maths is: fwhp = rwhp x 1/0.78 Im not complaining! Quote Link to comment Share on other sites More sharing options...
spikedjack Posted November 12, 2012 Share Posted November 12, 2012 I'm afraid you're both wrong. Its 568fwhp. The 22% is calculated from the fwhp, not the rwhp. The rwhp is the 78% that is left, so the correct maths is: fwhp = rwhp x 1/0.78 Correct, it's a loss from the fwhp not a gain from the rwhp. Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 12, 2012 Author Share Posted November 12, 2012 Here you are, Dave Baker was a real professional but lost heart with the job as companies with rolling roads were inflating power figures to create work and reputation. http://www.max-boost.co.uk/max-boost/internet_articles/Puma%20Race%20Engines%20Technical%20Guide%20-%20Measuring%20Engine%20power%20-%20engine%20dynos%20and%20rolling%20road%20dynos.htm and http://www.pugheaven.co.uk/Transmission%20Losses.htm Much appreciated Chris I've skimmed through the links tonight but will have a proper read tomorrow Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 13, 2012 Author Share Posted November 13, 2012 (edited) I think anyone who's seriously interested should read the links Chris posted. Especially the first one. The only sad part is there's no mention of an autobox but still lots of very good info. Did anyone check their tyre pressures before putting their car on the rollers as this appears to be the biggest area you lose hp ? Taken from the first link Some time ago I had three almost identical race cars set up together in a group session at a rolling road. The engines were very similar except for minor differences in the camshafts fitted. One showed 118 bhp at the wheels, another showed 124 and the third showed only 98. The operator spent ages I'm told (I wasn't there) trying to find why the third car was so poor. It wasn't till the next day when that particular owner was checking things before the race that he noticed that the tyres only had 7 psi in them - the car had sat unchecked over the winter and no-one had bothered to standardize the pressures before the dyno test. In the race, that car went just as well as the other two and if anything was slightly the fastest of the three. That gives you some idea of how much power a set of flat tyres can absorb. Edited November 13, 2012 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 13, 2012 Author Share Posted November 13, 2012 So reading back through this thread we already have a 7% difference of what two dyno shops use to equate whp back to flywheel hp on an auto. On a 300 whp figure this gives you 384 fwhp from one and 353 from another !! Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted November 13, 2012 Share Posted November 13, 2012 Rolling road figures have about as much reliability as a woman's reply when asked how much that dress cost. If you want accuracy pay for a proper engine dyno run, as Dnk says. I would take rolling road figures, especially none bolt to hub types, as a source of entertainment, that's all. A lot of graphs and figures are just laughable and would have you believe the basic premises of physics have been breached. Quote Link to comment Share on other sites More sharing options...
mellonman Posted November 13, 2012 Share Posted November 13, 2012 The goal of the story dont go number hunting its going to be wrong by up to 20 % my car goes like stink thats all i care about, who can actually put down all the estimated power anyway? not me not even when it was stock!! Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted November 13, 2012 Share Posted November 13, 2012 Personally I like to make a car put down as much of its existing power as well as possible before looking for more. I have ALWAYS found lap times respond more to suspension and tyre optimisation than to an extra 20% BHP unless the car is pro built and set up. Quote Link to comment Share on other sites More sharing options...
Jamesy Posted November 14, 2012 Share Posted November 14, 2012 Sam @ TDi told me the rule they use is 15% losses for a manual and 20% losses for autos - autos are actually around 22-23% he said but always quote lower so you dont look like you're trying to be a hero! Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 14, 2012 Author Share Posted November 14, 2012 From what i'm reading i don't think anyone really knows, to get an exact or within 1-2 % would take some serious testing starting with taking the engine out and getting it on an engine dyno to find out what its actual flywheel hp is to start with. Quote Link to comment Share on other sites More sharing options...
Jamesy Posted November 14, 2012 Share Posted November 14, 2012 From what i'm reading i don't think anyone really knows, to get an exact or within 1-2 % would take some serious testing starting with taking the engine out and getting it on an engine dyno to find out what its actual flywheel hp is to start with. yep, exactly!! Quote Link to comment Share on other sites More sharing options...
garethr Posted November 14, 2012 Share Posted November 14, 2012 (edited) The losses for a manual are calculated when the throttle is closed and the dyno is allowed to run to a standstill with the car in neutral. Dave Walker (Emerald ECUs) reckons that when he has had the opportunity to check calculated flywheel horsepower from a rolling road against the HP from an engine brake, the figures have been within a couple of BHP. This obviously relies on the integrity of the rolling road operator. http://www.emeraldm3d.com/rolling-road Unfortunately, you can't do the same for an auto, so any flywheel figure from a rolling road or hub dyno is guesswork. Edited November 14, 2012 by garethr (see edit history) Quote Link to comment Share on other sites More sharing options...
jcbt Posted November 14, 2012 Share Posted November 14, 2012 Sam @ TDi told me the rule they use is 15% losses for a manual and 20% losses for autos - autos are actually around 22-23% he said but always quote lower so you dont look like you're trying to be a hero! As my son Chris said when being mapped by Ryan at SRR my single auto was 550ish at flywheel and when dyno'ed at Dynodaze on sunday it was 447 at the wheels so it looks like the minus 20% on the autobox is about right but as already stated by a number of posters already its not deadly accurate but merely a general guide Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 14, 2012 Author Share Posted November 14, 2012 (edited) The losses for a manual are calculated when the throttle is closed and the dyno is allowed to run to a standstill with the car in neutral. Dave Walker (Emerald ECUs) reckons that when he has had the opportunity to check calculated flywheel horsepower from a rolling road against the HP from an engine brake, the figures have been within a couple of BHP. This obviously relies on the integrity of the rolling road operator. http://www.emeraldm3d.com/rolling-road Unfortunately, you can't do the same for an auto, so any flywheel figure from a rolling road or hub dyno is guesswork. Going by what you have just said then the fact that its an auto makes it pointless putting it on a rolling rd in the first place regardless of autobox transmission loss's. Too much guesswork for my liking Edited November 14, 2012 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
garethr Posted November 14, 2012 Share Posted November 14, 2012 The losses for a manual are calculated when the throttle is closed and the dyno is allowed to run to a standstill with the car in neutral. Dave Walker (Emerald ECUs) reckons that when he has had the opportunity to check calculated flywheel horsepower from a rolling road against the HP from an engine brake, the figures have been within a couple of BHP. This obviously relies on the integrity of the rolling road operator. http://www.emeraldm3d.com/rolling-road Unfortunately, you can't do the same for an auto, so any flywheel figure from a rolling road or hub dyno is guesswork. Going by what you have just said then the fact that it's an auto makes it pointless putting it on a rolling rd in the first place regardless of autobox transmission losses. Too much guesswork for my liking.It's not pointless... it's just that, unless someone has actually tested an engine on an engine brake and on a rolling road, the flywheel figure is based on a guess. Has anyone ever done that for a Supra? Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 14, 2012 Author Share Posted November 14, 2012 (edited) It's not pointless... it's just that, unless someone has actually tested an engine on an engine brake and on a rolling road, the flywheel figure is based on a guess. Has anyone ever done that for a Supra? Toyota If i had cash to burn which i don't i'd love to actually pull the motor and pop it on an engine dyno. But at the end of the day my cars an auto so other than for back to back testing of new parts there's no point in using one Edited November 14, 2012 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
scotty71 Posted November 14, 2012 Share Posted November 14, 2012 26.5% loss from fly>wheels for me last Sunday Seems quite high Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 14, 2012 Author Share Posted November 14, 2012 26.5% loss from fly>wheels for me last Sunday Seems quite high Can't see it being that high myself and think your motor is more likely to be around 355 fwhp running at the boost level you are. Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 14, 2012 Author Share Posted November 14, 2012 (edited) Read the first link CW posted scotty, theres a fair bit of it but well worth it Get your motor pulled and on an engine dyno scotty Edited November 14, 2012 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
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