Quote:
Originally Posted by uhn2000
BMW M is challenged because I think there is another very good reason they did not want to build this car with MT - the turbo lag. In the DCT model it is not very noticeable because you are not controlling the gear engagement, a computer is. But, with the MT you feel it more, especially on the gear down (engine braking is delayed). I feel that M engineers have tried to over compensate for the turbo lag on the launch of the car so as to have immediate power, but when you try a throttle blip to rev match a deceleration, the engine is still very high strung and does not climb back down as fast as an NA car would. In a weird way its easier to rev match, but you need to get used to driving around the Turbo. I believe that this is the reason that DCT is not rev matching in the V8TT like the V8 NA in the M3 - its the nature of the engine.
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Thanks for the thoughtful review. I'm one who agonized over the 6MT/DCT choice and finally went DCT out of respect for the designers' intent. I've never owned a car without a clutch pedal and truely enjoy the involvement of shifting myself. All in all, I'm happy with the DCT, but only because I have other cars to satisfy my need for 'involvement'.
Comments on the quoted section of your review are that the driver controls gear selection for the DCT in sequential mode, so as long as the clutch is engaged, lag is the same between 6MT and DCT. My assessment is that BMW has done a good job of minimizing lag (MUCH more responsive than my 335) but have not eliminated it.
I definately agree that the car gives its best when you drive with consideration for the fact that full torque will be on tap briefly after you ask for it, rather than immediately as on typical high performance NA engines. The flip side of this is that full torque at 2000 rpm on the F10M5 probably exceeds E60 torque at 6000 rpm, so the issue is less related to timing of power delivery as it is to 'feel' and controllability.
Your observation on engine response during throttle blips on downshifts is interesting. I've noticed something similar with the DCT and was blaming the gearbox. When downshifting on trailing throttle, the gear changes and half a heartbeat later engine braking kicks in like throwing out an anchor. I'm experimenting with a heal/toe action to reduce this effect and finding some good results. Note that from a technical perspective, turbos have less impact on the engine braking characteristics you describe than the throttle map does.
It's great to hear personal experiences from some who cares about the driving experience. Thx for posting!