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03-14-2013, 07:12 PM | #67 |
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Have any of the dct drivers been faced with extensive repair bills yet?
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03-14-2013, 07:14 PM | #68 | ||
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One should question how hard you're braking and does DCT downshift during braking. Someone already pointed it out, but was also wondering if the car is just downshifting: Quote:
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03-14-2013, 07:17 PM | #69 |
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Off the top of my head, one of the supercharged guys was due for a new transmission after abusing the car at the drag strip. I'm sure there are others, but replacement prices are not as bad as originally thought.
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03-14-2013, 07:21 PM | #70 | |
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Most of the problem with DCT lag has to do with the software. If your car is 2008-2009, you can get a DCT update from dealer after some good amount of complaints. Otherwise, you can get the DCT software reflash from Mike Benvo. I got the Euro DCT software where it starts with D instead of S. Also resolved the cold-start high-rpm shift jerk issue for me. I think the engine will be blown first before the DCT goes dead from all the abuse. |
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03-14-2013, 07:24 PM | #71 | |
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03-14-2013, 07:26 PM | #72 |
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I think he was trying to "launch" the car without using launch control...done multiple times if I'm not mistaken. With a non SC car, the results would likely be the same.
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03-14-2013, 11:14 PM | #73 | ||
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So, three shifts over a quarter mile equals a .45 second advantage for the auto, meaning a 3.6% disadvantage in terms of actual acceleration time for the stick car in this venue. Because the shifts happen early, middle and late during the run, I'll call the .45 second DCT advantage as averaged over the acceleration period. Therefore, because the DCT car is under power for 3.6% longer, think of this as an average added power of 3.6% during the run. Now, remember that trap speed (and ET) tend to vary as per the cube root of the power to weight delta. With this in mind, figure the DCT will have a 1.2% performance advantage, so a stick car might turn a 12.55@112.65. Of course, the stick car is lighter, so that further diminishes the difference. Therefore the close racing we looked at a bit earlier in this string. Quote:
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03-15-2013, 06:14 PM | #74 |
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To all those interested in the OT performance advantage of M-DCT vs. 6MT and in the very closely related issue of shift times:
http://www.m3post.com/forums/showthr...=582295&page=4 A bit tough to track the main thrusts from the players in that debate (myself included of course). In short some of the supercharged M3 drag racer guys felt that M-DCT could be good for an equivalent 50 hp and 10 mph trap speed advantage in the 1/4 mi. I actually argued strongly against that. However, again, it depends on exactly which contest you are trying to compare, 0-60, 60-130, 1/4 mi. time or trap, time to speed, time to distance, etc. In that discussion I actually began using some 0.2 (200 ms shift times). The drag racer guys insist from vbox data that 0.6 seconds is much more realistic. There is no one right answer here but I am fairly convinced most non-pro folks cannot consistently shift a production 6MT E9X M3 car in 0.2 seconds, certainly not without powershifting. To ascribe an equivalent power gain due to M-DCT is absolutely reasonable however, there is no one single best number for it. Bruce's rough estimate above seems to work out to 15 hp (3.6%). An absolutely critical factor in this is the shift time difference. The best estimates for the M-DCT are in the 50-100 ms range. My prior quick "back of the envelope" calculation showing a 60 hp advantage was not supposed to represent my best guess for the M-DCT advantage, just to show that there is one and how large it might be. Here is a reasonably large performance database of magazine test results: http://www.m3post.com/forums/showthr...=70737&page=15 Other than a single outlier in 2 contests the M-DCT cars are overall faster than the 6MT cars in the quarter mile and in many other contests. The best way too look at this is actually physics based simulations. The formulae Bruce and I have used above are decent approximations for some very quick "back of the envelope estimates". Better than those are a real simulator which is ideal for this type of problem, both because it captures the physics but also, very importantly because it holds ALL variables absolutely constant between the runs (such as temperature, tires, launch, weight, shift times (and other driver effects), parasitic losses, etc.). Below are simulations for a stock E92 M3 M-DCT vs. 4 different 6MT cars, equal power and then +20 hp, +40 hp and +60 hp. These results are based on a 50 ms M-DCT shift time and 400 ms 6MT shift time. They indicate, that depending on the contest, the M-DCT is good for somewhere between an equivalent 20-50 hp over the 6MT car. If you (or some theoretical you) can consistently shift in 200 ms this equivalent hp advantage figure will probably drop to about VERY ROUGHLY about half of this. I certainly could have run those simulations, but felt a bit lazy. Anyone should recall this basic fact - it take a lot of hp to make relatively small changes in ETs. This along with shift time savings for the M-DCT is the "equivalent hp" idea and it takes quite a bit of it to account for relatively small time savings. I think am truly done with this OT debate here. Hopefully, some fellow members can continue my effort in leading the thirsty to the river on this particular point.
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03-15-2013, 06:21 PM | #75 |
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The basic issue is your assumption of a 0.4 second 6MT shift speed. Seriously, that is a joke. I could teach a 15 year old to shift faster than that within a hour of so of teaching how to drive a stick. Nobody who has any business trying to drive a car at the strip will shift anywhere near that slow. Try cutting that in half.
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03-15-2013, 10:10 PM | #76 | |
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03-16-2013, 07:38 AM | #77 | |
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There is no possible way that you are going to see real world differences of 4mph in trap speed between these two cars when the 6MT is actually driven properly. Simulations are fun (I've used Cartest for many years going back to when it was a DOS program), but real world data is much more worthwhile as the model is only as good as it's inputs. In any event we might have a fun event this Spring sometime if a potential private rental goes through...should be a blast to gather real world data under the same conditions using the same rear wheels/tires.
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03-16-2013, 03:27 PM | #78 | ||
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One quick CarTest experiment I ran was to change the 6MT M3 shift time to be 50 ms faster. That increased the trap speed by almost exactly 1 full mph. It made a larger difference than I thought it would. Quote:
Again, for the hundredth time, the concept here remains completely solid, the M-DCT is faster because of shift time reduction and that can be thought of as equivalent hp. It is not an insignificant amount of equivalent power. A good side discussion but again, let's please get back to the lag discussion... We've probably lost any of the folks who might participate in that converstation...
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03-16-2013, 03:50 PM | #79 |
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We can agree to disagree I suppose. On a stock engine car, DCT will not give you 4 mph over a 6MT. All published test results such as C&Ds, for example, so at best a 1mph benefit to DCT although their results show no benefit in trap. All their M3 traps, 2x6MT and 2xDCT were within 1mph of each other at 113-114mph. I'll definitely agree you might eek out 2-3 tenths in ET if you can launch both just right (stock engines), but you're simply not going to gain 4mph trap on stock S65 M3s.
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03-17-2013, 12:19 AM | #81 |
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03-17-2013, 02:45 AM | #82 |
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I'll chime in...
I have a lag on mine as well, but it's not bad at all (barely noticeable). I already got used to it and doesn't bother me as I do not do much city driving anyways. |
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03-17-2013, 10:04 PM | #83 |
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Somewhere other than here? Thanks.
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03-17-2013, 10:12 PM | #84 | |
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My point has never been about an exact number. There is no such thing as an exact number, for ET gain, trap gain, hp gain, shift times, etc. There is also no such thing as exact real world test numbers either! Environmental, driver and individual car conditions vary too much. It is a GENERAL PRINCIPLE here. In my very first reply I was only "hitting" back at the thread polluters who were baiting (it worked) with all of the typical "should have got a MT" BS. In that original thread I stated the a M-DCT is good for an equivalent 25-50 hp depending on the contest. You've now "given me" a couple tenths, I think 4 tenths is more reasonable. Hopefully we can finally agree on the big picture and similarly may just be able to agree that there is not one right answer here.
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03-18-2013, 10:17 AM | #85 | |
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I fully comprehend that there is an acutal time required to engage one clutch while the other disengages and therefore a period of time where none of the clutches is fully engaged. This is essentially the DCT shift time and could well take 50-100ms depending of the shift mode. However, for the purpose discussed here, wouldn't the two clutches slip simultaneoulsy and therefore never interupt the drive force to the wheels (especially in the more aggressive modes)? Sorry for bringing this thread off topic again Last edited by CanAutM3; 03-18-2013 at 11:37 AM.. |
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03-18-2013, 11:11 AM | #86 | |
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You cannot compare this with a double clutch setup. |
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03-18-2013, 11:22 AM | #87 | |
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However, no work gets generated during a shift, since no force is being applied during that brief instant. The longer the shift, the bigger the work deficit. Swamp's conclusion is that, to match a DCT M3, a 6MT M3 would need to have 25-50 more hp to compensate for the work it is not producing during the longer shifts. Last edited by CanAutM3; 03-18-2013 at 12:41 PM.. |
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03-18-2013, 12:49 PM | #88 | |
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I think the best estimate, based on a variety of sources is 50-100 ms for a typical aggressive upshift. Also, shift times will vary depending on the Drivelogic mode and the level of agressiveness in the current driving.
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