bolarbag Posted July 18, 2008 Share Posted July 18, 2008 Is this always true in any instance with either an engine dyno or a 1:1 gear on a chasis dyno Is there any arguments known against this? I've a query - my idolised graph(Sorry Nic(GT35R)) doesn't x-over at this point but I notice that every graph on SRR does, is this why its the chosen rolling road amongst you and doesn't give 'conservative' figures but actually gives the true figures? I just rarely see this mentioned even in the states when folk post their dyno graphs, its not a new theory so I gather its wideknown What if the RR won't allow you to use 5th gear for your pull, is it a case of go elsewhere(if you want an accurate figure and graph)? If all chasis dyno's were to dyno@ 1:1 with a x-over point of 5252rpm wouldn't there be a lot less discrepancies over accuracies and uncertainties? I just wonder why anyone would want to dyno anything other than@ 1:1 and if it was widely known, would give us all an indication of performances between various cars across the country rather than having graphs that have big figures but dont mean $*%%?? Quote Link to comment Share on other sites More sharing options...
Wez Posted July 18, 2008 Share Posted July 18, 2008 I just wonder why anyone would want to dyno anything other than@ 1:1 and if it was widely known, would give us all an indication of performances between various cars across the country rather than having graphs that have big figures but dont mean $*%%?? SRR is an independant dyno, they dont offer tuning etc, therefore they have nothing to gain from inflating the figures. Tuning houses with dynos have to show that the money people have spent is worth it, just my opinion Quote Link to comment Share on other sites More sharing options...
garethr Posted July 18, 2008 Share Posted July 18, 2008 (edited) It's nothing to do with gear ratios, just the mathematical formula which converts torque (measured by the dyno) to brake horsepower (used for bragging on car forums). BHP = RPM * force in lb/ft / 5252 Thus, if RPM = 5252, BHP = torque in ft/lb. P.S. This is true only for imperial measurements. http://en.wikipedia.org/wiki/Dynamometer Edited July 18, 2008 by garethr (see edit history) Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted July 18, 2008 Share Posted July 18, 2008 It's nothing to do with gear ratios, just the mathematical formula which converts torque (measured by the dyno) to brake horsepower (used for bragging on car forums). BHP = RPM * force in lb/ft / 5252 Thus, if RPM = 5252, BHP = torque in ft/lb. When the curves cross over, BHP = Torque, therefore Power / Torque = 1 Rearranging the original formula... Power / Torque = RPM / 5252 Substituting... 1 = RPM / 5252 hence, at 5252 rpm, the power and torque curves must cross. QED Quote Link to comment Share on other sites More sharing options...
bolarbag Posted July 18, 2008 Author Share Posted July 18, 2008 It's nothing to do with gear ratios, just the mathematical formula which converts torque (measured by the dyno) to brake horsepower (used for bragging on car forums). :blink:It is if your using a chasis dyno, that's probably 99.9% of us then, if you dont measure at 1:1 then your getting an inaccurate measurement of torque(or its a calculation) one of your main values in your mathematical calculation of bhp, it wouldn't only be useful for bragging if all other variables were measured correctly in the first place I now have the utmost respect for SRR dyno graphs:cool: Quote Link to comment Share on other sites More sharing options...
Alex Posted July 18, 2008 Share Posted July 18, 2008 Are the 2 scales up the side the same?? If the lines aren't 100bhp and 100lb/ft....then the lines won't cross at that point... Quote Link to comment Share on other sites More sharing options...
bolarbag Posted July 18, 2008 Author Share Posted July 18, 2008 Are the 2 scales up the side the same?? If the lines aren't 100bhp and 100lb/ft....then the lines won't cross at that point... I know its a Fri but....??? Quote Link to comment Share on other sites More sharing options...
garethr Posted July 18, 2008 Share Posted July 18, 2008 (edited) It is if you're using a chasis dyno, that's probably 99.9% of us then, if you don't measure at 1:1 then you're getting an inaccurate measurement of torque (or it's a calculation) one of your main values in your mathematical calculation of bhp. It wouldn't only be useful for bragging if all other variables were measured correctly in the first place. I now have the utmost respect for SRR dyno graphs It doesn't matter if the measured torque is accurate or not, the curves still cross at 5252 rpm. It's just that the BHP is as inaccurate as the torque is. The overall ratio is never 1:1 anyway, because of the diff and the wheels. The dyno knows the wheel RPM, the engine RPM, and it's measuring the torque at the wheels. After that, it's mathematics. In theory, the result should be the same in any gear -- lower gear = more torque, but lower roller RPM. However.... in practice, a lower gear will apparently give a false, high, result: http://www.emeraldm3d.com/em_r_road.html "Flywheel" horsepower is a different matter...... especially on an auto. Edited July 18, 2008 by garethr (see edit history) Quote Link to comment Share on other sites More sharing options...
bolarbag Posted July 18, 2008 Author Share Posted July 18, 2008 It doesn't matter if the measured torque is accurate or not, the curves still cross at 5252 rpm. So to confirm, if a dynograph with torque and bhp plotted doesn't crossover at 5252rpm then the graph is false, regardless of gear? Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 18, 2008 Share Posted July 18, 2008 So to confirm, if a dynograph with torque and bhp plotted doesn't crossover at 5252rpm then the graph is false, regardless of gear? Absolutely. Quote Link to comment Share on other sites More sharing options...
Lee P Posted July 18, 2008 Share Posted July 18, 2008 I've a query - my idolised graph(Sorry Nic(GT35R)) doesn't x-over at this point but I notice that every graph on SRR does, is this why its the chosen rolling road amongst you and doesn't give 'conservative' figures but actually gives the true figures? Looking at Nic's graph it looks like it shows back to back runs. So both the lines are horsepower, I could be wrong but thats what it looks like to me. Quote Link to comment Share on other sites More sharing options...
bolarbag Posted July 18, 2008 Author Share Posted July 18, 2008 (edited) Thats good then, I had intended to take the long trip to SRR, but was put off by the extra fuel costs as I could maybe have had it cheaper at Dastek, They want me to do the pull in 4th - No They wanted to charge extra because it was a motec LMAO:search: The use of their special com's equipment to hook up to the Motec(That would be an XLR connector, a few leads and either a serial lead or a USB wired in that I have in the car already) They also said they would have to wait months for this 'special' comms equipment - by this time the big red button was getting pressed:) Looking at Nic's graph it looks like it shows back to back runs. So both the lines are horsepower, I could be wrong but thats what it looks like to me. That would make a fair bit more sense, so torque is around 510ftlb, that would be about right for a GT35R and the associated mods, I just had a look there as I couldnt find it my confidence in this setup is instilled:) Edited July 18, 2008 by bolarbag (see edit history) Quote Link to comment Share on other sites More sharing options...
Ian C Posted July 18, 2008 Share Posted July 18, 2008 (edited) What Alex meant was, most dyno graphs have the vertical scale for horsepower on the left, and torque on the right. If the scale is different then the lines won't cross in the right place, e.g. the top of the left hand scale is 500bhp but the right hand scale is 400ft/lbs, then it'll be way off. The SCA one I got is like that, the torque scale on the right doesn't correspond with the bhp scale on the left, so no crossover. The SRR one I got corresponds so it crosses in the correct place. See attached. -Ian Edit - if you look at the SCA one, at about 5252 revs the torque figure is about 450ft/lbs and the power one (the line in bold) is at 450bhp, so in fact they do correctly "cross" there, but due to the scale being different, it looks like they don't. Edited July 18, 2008 by Ian C additional info (see edit history) Quote Link to comment Share on other sites More sharing options...
bolarbag Posted July 18, 2008 Author Share Posted July 18, 2008 AHHHHHHH!!!Sorry Alex - I'm thinking horizontal, vertical only, I was like wtf?? I did have your first graph and did wonder...all is explained;) I was wondering is SRR the only proper dyno!!!???lol Quote Link to comment Share on other sites More sharing options...
Ian C Posted July 18, 2008 Share Posted July 18, 2008 I like SCA, they are near me, nice bunch, they respect me and don't try to sell me junk, maybe the dyno over-read or maybe I detuned it a bit since, can't recall, but otherwise it's a nice setup and they had no reason to overinflate the numbers. Big fans and big hoses to help deliver air direct to the air filter too. -Ian Quote Link to comment Share on other sites More sharing options...
bolarbag Posted July 18, 2008 Author Share Posted July 18, 2008 I like SCA, they are near me, nice bunch, they respect me and don't try to sell me junk, maybe the dyno over-read or maybe I detuned it a bit since, can't recall, but otherwise it's a nice setup and they had no reason to overinflate the numbers. Big fans and big hoses to help deliver air direct to the air filter too. Yeah don't get me wrong, even if they do over read as long as they over read at a consistant level then your laughing - and its a plus they don't try to sell ya boll££ But then who says they over read if they allow ya a 5th gear pull and they have the x-over point spot on:innocent: I do agree though its a fair bit out than I'd have hoped, so maybe my dream of harmonised proper Dynos isn't the way forward:) Quote Link to comment Share on other sites More sharing options...
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