09-30-2013, 11:56 PM | #177 | |
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10-01-2013, 03:03 PM | #178 | |
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What are the extra variables in these formulas to compute tire compound, size, wheel spin, imperfections in the road, size of drivers balls, wind conditions, etc. |
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10-01-2013, 03:17 PM | #179 | |
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Part of the issue is that tests conducted in the real world also vary. This sounds obvious, but I'm sure you are not appreciating the subtlety involved. There is no one right (test based) answer for any given performance metric for any given car - there is a range of realized results in the real world. This variation is significant. Simulation provides a benefit because it truly removes most of the uncontrollable variations that occur in the physical world. Driver and environmental conditions remain as the most significant variables that contribute to producing this variation. These conditions are ENTIRELY eliminated through simulation in that they can be absolutely identical each and every "test". To some extent these can be addressed with simulation. Launch rpm, launch technique and tire friction can all be modified from nominal values. Furthermore tire friction both static and dynamic friction are used in the tool I use regularly and the tool I wrote myself. Of course shift times can be altered from novice to expert drag racer to DCT shift times. Furthermore these effects can be isolated and explored individually! The power of physics as a truly predictive science should not be underestimated. Similarly it's limitations, uncertainties and applicability must be understood and respected. I'm probably barking up the wrong tree but I hope this helps.
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10-01-2013, 04:03 PM | #180 |
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10-01-2013, 04:58 PM | #181 |
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10-01-2013, 05:32 PM | #182 | ||
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But this car will not do sub 12 sec 1/4mi times. Thats at best with no friction from tires and air . Id rather have similar 1/4 mi times to the current car but with significant increase in trap speed so that the car is actually faster (not just in such a short distance) if that makes sense. |
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10-03-2013, 06:14 PM | #183 |
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Swamp could you reverse the plotting order of your curves (plotting the highest gear first, lowest gear last), this would better show the optimal shifting points occuring much below redline for the boosted M4 engine.
Also typo correction, in your original post 2nd to last paragraph you typed M4, instead of M3 (E92) in "whereas the M4 tapers off much less dramatically". These curves show in a mathematical way what could be expected that a turbo engine is going to be much less pleasurable to drive than naturally aspirated. Simply because turbos cannot spool fast enough to keep a low compression ratio engine (off boost) breathing at high RPM AND have zero lag at low RPM. This will not be a driver's car (as far as the engine is concerned for starters) the way the E92 and E46 are. Yes, it is going to be silly/idiotic kind of fun in the low to midrange RPM because of the available torque, but not the mature linear high reving fun that is much more exhilarating from a naturally aspirated engine. Now I understand why all the M4 used for the taxi ride BMW pre-views with BMW DTM drivers were all manuals. Any efficiently designed DCT will not use the upper RPM range above the optimal crossing. So it should sound even more dull than the manuals. The only way to improve this situation with a DCT is to have as many gears as possible, that means not 7 but 10 or more. Obviously this isn't possible and desirable. So that's it, this engine is essentially wothless above those RPMs. Even for mileage. The only benefit for going to redline will be sound and we already know it is not going to be the forte for that engine. Last edited by V8FunNaturally; 10-03-2013 at 10:03 PM.. |
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10-03-2013, 10:23 PM | #184 |
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Although its a bit early to speculate with power and weight still not precisely know but I'd be willing to bet that some journalist will crack into the 11s with the car.
Times and traps correlate pretty well. Yes you can have two cars with the same time and one trapping slower or faster. Either way power to weight is what drives improvement in both. Thus what you hope for is next to impossible.
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10-03-2013, 10:29 PM | #185 | |||||
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However, it remains a good question as to what the DCT shift points will be. Perhaps the differences between redline and optimal shifts will be very small in favor of the optimal point and BMW will take the "phony" route and choose redline just for more excitement. Doubly (or I guess triply when you consider your point about acoustics...) contradictory since the car is already dropping in redline regardless of shift points.
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10-04-2013, 12:08 AM | #186 |
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Totally different engine, but I drove the 428i yesterday. I'm sure that also would come up with a "shift before redline" characteristic. But what a fun little engine!!! No way did I ever feel the need, or even desire, to short shift! It just pulled to the redline in every gear and really seemed to want to be driven that way as well!
That engine won me over by it's willingness to rev and very unlaggy response! I'm sure that it also can be beneficial to do short shifting during some types of driving. The thing is, a simulation cannot recreate how a engine sounds and feels in real life! Not sure whether the 428i has active sound, but it even sounded great on the inside!!! My guess is that people who dismiss the S55 might be in for a surprise... |
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10-04-2013, 12:41 AM | #187 | |
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There is a +10mph difference in the 458 and mclaren mp??? Vs the gtr. Same 12sec times. 10 mph you are gaining and passing pretty significantly at those speeds. Thats all i was referring to. Plus I believe trap speed is a good indication of power to weight where as times are an indication of traction and launch eg. Awd. So using your own idea of power to weight, we should be looking at trap speeds not 1/4mi times. No? |
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10-04-2013, 02:09 AM | #188 | |
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For some "math" behind this have a look here. The quality of the regression (curve fits) for trap speed vs. power to weight is a bit higher than for time vs. power to weight. In the math language the former simply has a larger R^2 value. The difference though is not too large! Also on the same page note the truly excellent correlation between 0-60 time and 1/4 mi time. Basic common sense, have a high power to weight AND get a good 0-60 (i.e. good launch) and you will have a similarly good 1/4 mi time.
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10-04-2013, 02:41 PM | #189 |
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Here are my thoughts of the ideal ratios for the F8X DCT. These ratios would allow to keep the engine mostly in the power plateau (5700-7300); with redline shifts (7500RPM) in each gear that would drop the RPM to 5600 in the next gear. This would also yield a nice lofty mpg oriented 7th gear for 1850RPM cruising at 100km/h. (Note: I am assuming a power curve for which the power drop off at 7500RPM is equal to the power at 5600RPM)
FD 3.154 RPM km/h 1 4.310 7500 70 2 3.218 7500 94 3 2.403 7500 126 4 1.794 7500 169 5 1.340 7500 226 6 1.000 7500 303 7 0.747 1850 100 |
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10-04-2013, 03:50 PM | #190 | |
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10-04-2013, 11:47 PM | #191 | |
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10-05-2013, 02:29 AM | #192 | |
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As I mentioned the other day, I drove the 428i and was really amazed by that engines characteristics. It was really egging you on to take it to the redline. Not just for 0-100km/h acceleration, but also for overtaking or "just for fun". Unlike the M550d I drove a while ago, which really wanted you to shortshift, this engine felt so much more like a highly tuned NA engine in it's power delivery. Much more so than the N55 (in a 640i), which I frankly found a bit underwhelming... That 428i put a BIG smile on my face. Possibly because I was so pleasantly surprised by it. I had driven a N20 320i and that felt more similar to the N55 in it's power delivery. The 428i however was like a different engine! My point is, the N20 2,8i version, has a power graph as you can see here. Not sure if you want to do all the calculations/analysis, but shouldn't this engine also, on paper, be a engine that should favour short shifting? It could possibly be that short shifting gives a few tenths better acceleration, but the engine really wants to go to the redline! Which feels really fun and inspiring, unlike the M550d where you just want to change up way before redline. If the analysis shows that the N20 2.8i engine also "should" be shortshifted, I would say that one should reserve judgement on how the S55 will feel until it has been driven. |
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10-05-2013, 06:13 AM | #193 | |
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If you want to input in CarTest, use the following. I am curious to see the results. RPM Tq Hp 1500 246 70 1600 296 90 1700 346 112 1800 396 136 1900 396 143 2000 396 151 2100 396 158 2200 396 166 2300 396 173 2400 396 181 2500 396 188 2600 396 196 2700 396 204 2800 396 211 2900 396 219 3000 396 226 3100 396 234 3200 396 241 3300 396 249 3400 396 256 3500 396 264 3600 396 271 3700 396 279 3800 396 287 3900 396 294 4000 396 302 4100 396 309 4200 396 317 4300 396 324 4400 396 332 4500 396 339 4600 396 347 4700 396 354 4800 396 362 4900 396 369 5000 396 377 5100 396 385 5200 396 392 5300 396 400 5400 396 407 5500 396 415 5600 396 422 5700 396 430 5800 389 430 5900 383 430 6000 376 430 6100 370 430 6200 364 430 6300 358 430 6400 353 430 6500 347 430 6600 342 430 6700 337 430 6800 332 430 6900 327 430 7000 323 430 7100 318 430 7200 314 430 7300 309 430 7400 302 426 7500 296 422 |
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10-05-2013, 06:29 AM | #194 | |
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10-05-2013, 02:34 PM | #195 | |
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Torque is simply falling too fast above ~5500 rpm to "have room" for the force curves not to cross!
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10-05-2013, 02:38 PM | #196 | |
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I have no problem to run an analysis for the 320i, just give me hp from 1000-redline in 500 rpm increments, confirm redline and each gear ratio and the final drive. It is quick with this information. That being said, it appears pretty obvious from inspection that this car will need to be short shifted for optimum performance.
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10-05-2013, 02:55 PM | #197 |
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By the way I don't think a (fixed) ratio between ratio is at all a standard transmission gear selection technique. It produces very odd shaped speed in gear curves compared to most similar BMWs. More typical is an even spacing on the rpm vs. vehicle speed plots. Below I've shown yours and the M3 M-DCT. The 1M 6MT is not too dissimilar from the M3.
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10-05-2013, 03:04 PM | #198 | |
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I am really looking forward to the first test drive reviews of the F8x What will the S55 feel like? Does it want to rev etc? The day I drove the 428i I also drove a E36 M3 3,2. The intersting thing is that the 428i felt more spectacular and entertaining during acceleration. The 428i even had more/better engine noise inside the cabin during hard acceleration and definitely felt quicker. I'm a devoted fan of the BMW I6 engine, but the E36 M3 engine actually felt, dare I say it, uninspiring compared with the N20 in the 428i... The E36 M3 just has a steady and "slow" rise in revs to redline. The 428i just felt meatier at every stage of the rev scale. I'm sure I still would choose the M3 engine for exhaust sound and smoothness, but that 428i engine just put a big smile on my face. Even though it's slower from 0-100km/h it just feels more spectacular!! I NEVER thought I'd write what I just did. But that was before I drove the 428i. It felt fast, and it sounded like a sports car engine from the drivers seat, which probably also "helped" my perception of it Probably active sound? |
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