07-26-2014, 02:02 AM | #1 | |
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Further dyno evidence of no under rating
This is a repost but after that crap thread some time ago about the Motor Trend E92 vs F82 dyno testing I felt this deserved its own post.
In short, using a novel and accurate wheel based in-situ dyno, there is no evidence of any significant under rating of the F82 M4. Although the dyno came back at 449 PS is was acknowledged that a small unrealistic blip in the power curve (see graph below) means that a more realistic number is about 440 PS (434 hp) and that is a 2% under rating (factory claimed is 431 PS which is 425 hp). Member Boss330 provided the following translation from the article: Quote:
What is innovative about this Insoric RealPower dyno system (link) is that it accounts for drivetrain inertia and losses by measuring wheel hp during an actual acceleration run. It then uses coast down data to calculate (and perhaps estimate) various loses (tires, aero, drive train). And with accurate wheel power and accurate losses one can then get accurate crank power. Boss330 and I have some outstanding emails to the company to better clarify how the coast down measures losses. One additional data point as to the accuracy of this system is that for the Aston Martin V12 Vantage is measured 566 PS and the stated spec is 573 PS. That is about a 1% error (of course assuming that the car is neither under nor over rated). Last but not least you might note that the M4 vertical axis is mislabeled. In a reader letter the next month Auto Bild clarified that the values and graphs they provided were correct it was just a mislabeled axis value.
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07-26-2014, 02:58 AM | #3 |
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Tough to declare if their methodology is actually accurate as you state. Bench marking it against other cars (aston martin marketing) with the presumption of no over/under estimate introduces further uncertainty. Most analysis software you've cited does curve fitting to empirical results - a common initial approach to more rigorous modeling in academia. It would be more interesting if we had dynamic finite element analysis to simulate dynos using sound mechanical engineering theory. I have a friend in BMW technology who does just this to examine engine stresses - I might reach out to him to see if he has theoretical baselines for the M3 and other competitor cars through FEA modeling.
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07-26-2014, 04:44 AM | #4 |
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Underrated or not I do not know but what is fact is that when they've put E92 M3 and F80 on the same dynos F80 has shown the difference between the two is significant and does not represent a claimed 10hp gain for the F80 model over E92. Was E92 overrated then?!
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07-26-2014, 05:29 AM | #5 |
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This is what I have struggled with. So much conflicting data that doesn't add up. Comparison dynos showing very significant differences between E9x and F8x. Trap speeds in excess of 120mph. Some dynos suggesting a higher rating and some lower. To me, I don't see how we can possibly conclude either way at this point BUT it does seem like there is "more" evidence that there is some level of underrating.
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07-26-2014, 07:55 AM | #6 |
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lol at butthurt e92 owner.. that "small unrealistic blip" wasn't on the other graphs we have seen was it?
just accept the F8X pretty much obliterated the E9x on the dyno |
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07-26-2014, 08:31 AM | #7 |
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I find it neither small, nor unrealistic, that 'blip'. Unless, of course, you expect max power to really cover the whole plateau like in the official charts. That blip does seem to have about the size of a NA engines' power peak. Anyway, 440 or 449 PS is evidence of underrating and not evidence of no underrating, albeit it indicates that 460 or even 480 PS was a bit optimistic.
My favorite quote from the article: "Gigantisch: volle Leistung bis zum Begrenzer - das schafft kein anderer Turbo" If you take a close look to the upper end of the chart you can see that another nice little detail is underrated: Power sustains better, up to the limiter, than officially claimed. Thanks for sharing the info and explaining the dyno. |
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07-26-2014, 09:33 AM | #8 | ||
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Also, for most of these simulation a kinematic rigid model would suffice over a more difficult to construct finite element model. Either way I'm not sure such a model could solver this problem definitively, just way too many unknowns. I have access to a full complement of these tools as this is my profession.
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07-26-2014, 09:35 AM | #9 | |
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I like the new cars. I'm just likely not going to buying one soon. If you know anything about my leanings here on the forum you would know this is rubbish. The performance of the car and the wallop it gives the current car is entirely undisputed. My motivations are much more about the science of vehicles. Anyway, 2% is absolutely within the limit of the error from measurement. No conclusion can be made about under rating from this number.
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07-26-2014, 09:39 AM | #10 |
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Yes, that is exactly what I expect and should be expected. Such blips are not realistic in a crank/engine dynos. Have you ever seen one? Such dynos are very carefully controlled, thermally and air flow wise and are conducted over a long-ish measurement period at a very steady rpm which eliminates all intertial effects, engine and drivetrain.
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07-26-2014, 10:56 AM | #11 | |
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For full disclosure these threads annoy me because there's a lot of pseudo-technical mumbo-jumbo words, but that's balanced by the content behind them which seem solid to me. And I have no idea what your motivation is, but you do drop some knowledge bombs, so |
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07-26-2014, 11:35 AM | #12 |
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What I've seen this far the S55 has consistently put down about 70 rwhp more than the S65 has on dynos of the same type. When compared directly to an S65 on the same dyno it also put down about 70 hp more. It will take more than using an AM as reference to convince me that it's not significantly under rated given that the S65 is not severely overrated which don't seem likely at this point in time. That the F8X has put down close to rated crank hp at the wheels at the majority of dyno runs is IMO further evidence of grave under rating since I doubt all those dynos are THAT much off. In the end pick what you like, if you prefer to think it's not under rated you can find a data point or two to support you while ignoring the rest. Personally I don't really care what the exact crank or rw hp number is. Whatever make you happy I guess.
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07-26-2014, 11:53 AM | #13 | |
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07-26-2014, 11:55 AM | #14 |
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I just find it completely laughable that the thread title is "Further dyno evidence of no under rating" but then in the first post the OP says "and that is a 2% under rating". Contradiction much?
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07-26-2014, 12:22 PM | #15 | |
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07-26-2014, 03:12 PM | #16 | |
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Analysis software would introduce results in a vacuum. furthermore, you could even develop a probabilistically based approach for nonlinear inelastic dynamic finite element analysis and come up with median values that would be more reliable than focusing on singular dynos. Errors would be limited if we could use the cad (to transform into FEA) or finite element model files from the manufacturers themselves (which could be mapped into one consistent program). Doing so would allow for replicable analysis with simulated vacuum conditions limiting variance in extrinsic testing condition properties. Doing so would allow you to consistently use the same modeling approach with again nonlinear and inelastic material deformation to capture small deformations (due to transmission movement and other car component movement) and thermal properties (something typically missing in rigid kinematic modeling) further limiting analysis spread error. I too have access to a host of these tools as I helped google develop some of their technology behind their self driving car while I was a student at that institute of technology in massachusetts. Last edited by Stevens21234; 07-26-2014 at 03:19 PM.. |
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07-26-2014, 07:02 PM | #18 | |
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If you like feel free to think of a more accurate title to be "further dyno evidence indicates no under rating within reasonable bounds of experimental error". Sheesh, we aren't authoring peer reviewed scientific literature here...
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07-26-2014, 07:06 PM | #19 | |
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07-26-2014, 07:20 PM | #20 | |
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By the way, I do believe this car is making somewhere between 440-450. If you don't like that and want to waste your time disproving everyone else (or making yourself believe other things) Most people are basing the differences on what they are seeing in real life. Sure, some believe the car is making 500 crank, but it's not. The thing that dynos give us though, is deltas. And when you look at deltas between E9x and F8x cars, there IS a significant difference. It could be the highest or lowest rating dyno in the world and the deltas still matter-not for the absolutes, but for reference points. That's how it has been, and that's how it will always be. You can continue to combat those ideals all you want, but it won't change.
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07-26-2014, 07:26 PM | #21 |
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07-26-2014, 08:22 PM | #22 |
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I feel like I'm picking up my kids at school, with all the "Butt-Hurt" commentary that seems to show up here in disproportionate amount, even relative to the school. Nowhere did Swamp even bring in the S65 into the picture or claim that the old car was as fast as the new one. The whole thesis is that the shape of the curve, with flat constant, full power over a very wide RPM range is responsible for how quick the M4 is. I personally think its extremely interesting and I have learned many things from swamp and others in these analyses, they touch on something that I love and gets my neurons firing outside my area of expertise.
I also think the Insoric is extremely interesting tool, especially the "coast down" feature which will help estimate driveline losses. I would love to use this tool, the BT tool and actual moment calculations (which come directly from the ECU and is what the ECU believes to be the power given all the real time inputs), plus a similar Dash Dyno tool that I use, where you enter (and can calculate) gear ratios, temperature, frontal area, pressure, etc and it plugs into the ECU to get speed, acceleration to obtain a rolling road whp calculation. Between all of these we can triangulate a true dyno plot with full heat exchange and very accurate estimates of driveline losses over an rpm range (that go far beyond the traditional "divide by .85" to convert from driveline to bhp). I've said this many times in M3 post, the wheel dynos leave a lot to be desired with huge variation, no matter many are in whatever database is out there. |
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