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      06-03-2013, 11:49 PM   #62
swamp2
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Drives: E92 M3
Join Date: Sep 2006
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Quote:
Originally Posted by ASAP View Post
450 crank translates to 382 WHP assuming a 15% drivetrain loss but since BMW underrattes their cars I will give u 395 WHP... at 3450 LBS, that will not run 120, sorry... That DCT would have to be magic. For reference, my friend dynod 425 in a DCT 335is and hit 120.4 barely... This was with very lightweight wheels too on one of the fastest tracks in the country...
I believe that current E92 M3s are not overrated and are running about 11-12% loss. One very solid source of truly accurate loss information is the Rotortest Research Institute, rri.se, check it out. This is what a real repeatable dyno capable of absolute predictions looks like... I trust other Mustangs and Dynojets and the like about as far as I can throw them...

Let's get to the main point here though with another approach. Your guesses/observations are fundamentally rooted in a cars power to weight ratio, correct? Have a look at the "state of the art" in predictions of trap speeds based on power to weight alone. Generally speaking it is much less accurate than a physics based simulation approach used in my OP but it still offers some definite insights and you might relate to it better. LRT best fit regression. Now if you are better at curve fitting large, complex data sets, IN YOUR HEAD, than this formula, feel free to let me know. However, I doubt it. Humans tend to get pretty good at such curve fitting and extrapolation but you CANNOT ON AVERAGE beat the formula. That basically the definition of the curve fit formula...

For a 440 crank hp E92 M3 (give me 25 hp on top of 414 for DCT, that is a minimal number) with a weight with driver of 3700 lb. The formula above predicts an trap speed of 113 mph. Not bad for a quick first pass formula, eh!? The best time for a stock E92 M3 in the database I referred to earlier is about 115 mph. Let's say the formula is under predicting by 2 mph (you could also figure out if that a higher power figure is better, which in this case might indicate some underrating). For the sake of simplicity I'll stick with this approach. The formula certainly can not predict each and every car perfectly, with this simple model so many variables are not accounted for. However, it captures the simplest dominant effect of power to weight ratio.

Next for the M4 lets use 475 hp (450 actual + 25 for DCT benefits), with a weight with driver of 3600 we get 117 mph from the formula. You might personally have a gut feel that this number is "just about right". However, giving the same +2 mph of difference between observation and predictions for the current E92 M3 we then arrive at 119 mph. Hmmm....

Maybe 120 mph really isn't too unreasonable.

Maybe we'll also never see 123 out in the real world. As a small aside though I have noticed that trap speeds from CarTest are not its strongest prediction capability. I've received some valid criticism of my prior work on the forum where trap speeds are a bit under predicted compared to the best achieved results from real tests. Note that 113 mph and change from CarTest for the current E92 M3 whereas 115 is a better best figure! It is all coming together for you?

I do hope there is some of this getting through to you, it's actually some really good stuff in my humble opinion.
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E92 M3 | Space Gray on Fox Red | M-DCT | CF Roof | RAC RG63 Wheels | Brembo 380mm BBK |
| Vorsteiner Ti Exhaust | Matte Black Grilles/Side Gills/Rear Emblem/Mirrors |
| Alekshop Back up Camera | GP Thunders | BMW Aluminum Pedals | Elite Angels |
| XPEL Full Front Wrap | Hardwired V1 | Interior Xenon Light Kit |

Last edited by swamp2; 06-04-2013 at 12:04 AM..