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Originally Posted by swamp2
Rebuttal...
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I appreciate the thorough and detailed response. I noticed a few things below I wanted to address. I wanted to say right up front that some of the educational corrections seem wrong themselves. So I wanted to add our knowledge to the topic and hopefully help bring more understanding to this thread.
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Originally Posted by swamp2
And P1 Motorcars does tuning and have a Dynojet and thus have an inherent conflict of interest to "prove" that dynos and in particular Dynojets are accurate. Your entire argument here begins with this proposition that chassis dynos are accurate and that is a big problem. More on that in a bit.
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Our posts tell of our experiences and expertise and what we brought to the table to this topic. Nothing more, nothing less.
Correction: vBox hardware and vBox software (by RaceLogic) doesn't calculate NHRA trap speeds. vboxtools.com software used in our article has full NHRA settings, 1-ft rollout, and trap speed calculations. That's why both vMax and trap speeds are called out separately in our article.
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Maha dyno's and crank horsepower...
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Correction: We have a partner shop that has a Maha. I saw a few of the Maha comments in your thread and noted the people didn't understand what they measure, what they report, and how they work. I didn't read any further at that point. All of our prior analysis and success using CarTest to match real-world results has always been with Dynojet results. We added the Maha comparison as an afterthought. Even though we stand by those results and note they seem to be just as accurate as our Dynojet results, we'd prefer to ignore them and instead concentrate on the Dynojet results.
Correction: We know the differences between most different dyno brands. Some use F=M*A, others use strain gauges, others use eddy current + strain gauges, you get the idea. The different measuring techniques report different results. In our prior works, we used Dynojets and all simulations matched the real-world.
Correction: The 13% power changes you're talking about on the S65 may be more understandable the more you study their sources. I know you've been around long enough to see this analysis before. 91 Octane vs. 93 Octane and 6MT vs. DCT both account for some of those differences. Then sometime around late 2010 or early 2011, a software update was introduced that bumped base power significantly. By memory, I think it was about 10 whp bump. I've seen multiple independent vendors report the same increase in power at about the same time.
Correction: We cut-paste those all from your thread (also without attribution...sorry). We threw out the items you called outliers and non-DCT entries. The car in this test is an M3, not M4. If there are any missing items or cherry-picks, as of today, I still don't see them added to your own list.
- Good idea on the tire size calculations.
- We changed tire pressure because we measured it.
- We used 175 pound driver because that's what we were told it was.
- DCT shift times. I will confirm that we use 50ms.
Correction: There are white papers on the accuracy of SAE corrections. The paper's I've read showed them to be much more accurate than most people think. It's ironic reading people arguing against the accuracy of the correction, but also arguing the EEC regulations are enforceable law (which depend on the accuracy of these calculations).
Correction: Yes we've read the SAE documents. Without this knowledge, we wouldn't have been able to comment about the lacking humidity input in the Insoric section of our article. BTW, you forgot to mention the SAE correction also accounts for mechanical efficiency.
Agreed, it's a micro climate. But we always add it when we know it.
Correction: CarTest doesn't use them on wheel power simulations. Since we're using Dynojet wheel power simulations, we can skip this discussion as it doesn't affect any of our work or any of our results.
Correction:
- It sounds like they shared slightly more information with us about their hardware than they did with you. A vBox would still be more accurate.
- We pointed out the flaws in their various techniques by analyzing what they allow for input parameters. This isn't speculation, this is very obvious.
- Regarding Crr calculations. Have you tried changing tire pressure in CarTest and see how it changes the results? BTW, we used this formula for Crr: http://www.engineeringtoolbox.com/ro...ce-d_1303.html
I didn't see anything blaring that we supposedly did wrong. The most I got out of it was you don't play with wind and tire pressure, but we do. Our method is simple, yet time consuming. We use the actual results for each car and specific run. Our simulations always seem to match the real-world within a much tighter margin of error than 0.7 MPH using your approach. Yes it's philosophical approach and there’s a benefit to both. We didn't want to answer a theoretical question with theoretical data and draw iron-clad conclusions. We'd prefer to help draw conclusions based on actual data, and hopefully that's what we brought to the table.
One thing about the Dynojet models in CarTest. We can't speak for other dyno brands and we don't make any claims about them. All we're trying to say is that we have a track record of simulations that match real world data, and that track record is based on using Dynojet SAE corrected results. If it's not broken, don't fix it.
1. Chassis dynos, explained, we use Dynojet for CarTest simulations.
2. In-situ, wheel based, Insoric dyno, flawed,
3. Maha whp results, completely misunderstood
4. Trap speeds (and other performance metrics), consistent with simulations
5. BMW stated crank hp, BFD
6. Simulation, matches real-world results
7. Legal requirements, very interesting. SAE isn't a legal requirement, it's a standards body. Makes me wonder if EEC is the same thing. Now that I've read 3 or 4 of those documents, they don't appear to have any teeth in them whatsoever. Like the SAE, they sound like a standards body that if you want to put their stamp on something, you need to comply with their procedures. The later documents posted in this thread all but say it's voluntary. There are ample quotes by Boss330 from the EEC documents themselves that indicate that submission is purely voluntary; but once you submit, you are bound to the agreement. Again, sounds like it has absolutely no teeth in it whatsoever. But I'm also going to hedge my bets by saying I'm not an expert in anything regarding the EU.