Thread: M3 vs 335i
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      01-26-2008, 01:45 PM   #98
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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Originally Posted by sdiver68 View Post
It's OK, I welcome constructive criticism but not so fast on this count.

First of all, to clear up any miscommunication, I said for the track the M-DCT is "almost certainly better". Since no one has independently tested M-DCT I guess we'll have to wait and see before I remove the almost qualifier.

However, for a dual purpose car I'm not sure the distinction is so cut and dried.

A few points...

I would not call 92% efficiency "very close" to a MT which Bruce A. recently pointed out is about 96-97% efficient. That is 21 HP difference in the M3. A DCT may be a bit less efficient than a MT (concentric shaft, two clutches, etc.) but I bet they are very close.

I appreciate the advanced modern automatics but the article did not address complexity, number of parts, ease of service or those other niceties mentioned in the title of the article.

THE only reason DCT boxes are expensive now is their limited production quantities. Once the volume gets higher and price lower the flexibility and relative simplicity of DCTs will be really tough to match. Much of the flexibility of a DCT is in software.

Based on the recent videos of the M-DCT skipping gears seems entirely feasible (not that they actually showed that). Say 4-2: clutch on 4&2 shaft disengages, both 4 and 2 syncros move simultaneously, 4 disengage, 2 engage (they should each have their own actuator, right?), clutch on 4&2 engages. The only difference here is that you do not get smooth power transfer since you don't have the two clutches simultaneously engaging/disengaging. Like I have said, a DCT on a dual downshift can be as good as the best SMGs. A fairly small difference, esp. on downshift. Do keep in mind this is speculative.

Last edited by swamp2; 01-27-2008 at 04:16 AM.