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      03-14-2013, 08:18 AM   #34
Drives: 2011 M3, 2001 M5, etc
Join Date: Nov 2005
Location: Raleigh, NC

Posts: 450
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Originally Posted by swamp2 View Post
Yes, really.

Try a search on the forum if you are curious. Many threads and posts, both from me and some others arriving at our conclusions using both simulation, formulas, testing and magazine results.

It comes down to shift time reduction. If you assume the DCT can shift in about 50-100 ms which is a very reasonable number supported by a large variety of evidence, along with the fact that a good MT shift is probably in the 0.4 s range, just do some simple math. You save about 0.6 seconds over two shifts in the quarter mile. The math really is that simple time saved shifting directly translates to just about the same time spent over a certain fixed distance. For a 3700 lb car use the basic formula for a 1/4 mi time:

ET = 6.1178 (weight/hp)^1/3 (ref: , weight in lb, hp obviously as hp)

And you will find almost a 63 hp requirement to have this much gain!

This is a very rough version, I don't think the difference is trult that large, it is however, quite significant, no matter from what source you draw your conclusions.

Bottom line, if you line up two M3 with equivalent drivers, tires, road, launch, weight, one with M-DCT and one without. The M-DCT car will very decisively pull on the 6MT car. There is even a big enough difference that the 6MT driver could be quite a bit better and the M-DCT would still have the advantage.

Similar advantages exist on a track due, especially when 3rd gear is used a lot, which on many track it is. There is 12% more torque to the wheels comparing both cars in 3rd gear simply because of the gear ratios.

back at ya...
A good manual driver will be way faster than 0.4 seconds. The 6MT is nowhere close to being 0.6 seconds slower in the 1/4 mile (when driven by a seriously competent driver that is ). The flip side of the coin is how well an experienced manual driver can nail a holeshot by being able to control the clutch to provide just the right amount of initial weight transfer coupled with just the right combo of clutch engagement versus throttle application for the conditions (tires, road surface, ambient temperature, etc). Said driver likely has down the ability to shift very quickly and would model in the range of 0.2 to 0.25 sec/shift.

As far as comparing torque to the wheels at any specific speed, realize that, just like differential ratio changes, when the shorter geared car has to upshift, the longer geared car is then putting down "more torque to the wheels" for the remainder of that gear until it has to upshift. It's not a clear cut choice as there are many variables including how the shorter geared car will require more shifts potentially over the measured distance (one reason why in something like comparing the E60 M5 6MT to SMG, the 6MT gains on the SMG car in the 1/4 due to one less shift required before the lights but it still just barely is behind in time at the end of course).

The problem with DCT is that the clutch engagement is an educated guess. It can't be anything but what was programmed into the system while an educated 6MT driver has an infinitely variable range of clutch modulation choices available to him/her. I think the ideal DCT setup would be to have a clutch pedal for daily maneuvering, parking lots, slowing down to make a 90 degree turn and then needing "just" the right amount of clutch engagement/throttle application, etc, etc.
Current Stable:
2011.5 M3 sedan 6MT, Silverstone, no sunroof, no EDC, but all other options
2001 M5 LeMans Blue/Silverstone
2006 330i 6MT Red/black, ZSP, Nav, etc.
2001 Audi S4 6MT; 1996 Volvo 850R wagon
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