The question has arisen several times about what has lower drivetrain losses, the DCT or the manual M3. We have seen information being circulated suggesting the DCT has lower drivetrain losses which is why it performs better which is simply incorrect and a case of pushing personal politics over the correct information.
The DCT performs better simply due to the shift speed despite weighing about 50 pounds more than the manual. With the way a dual clutch transmission works, it simply takes some additional engine power to operate. This is especially true in the case of wet clutches such as the Getrag unit in the M3 vs. dry as dry clutches do not have the additional loss created by pumping fluid into the housing. Dan Carney writes in this article
hosted on dctfacts.com, "A dry clutch setup enjoys a 1% fuel economy benefit compared to a wet clutch DCT because of the elimination of the oil pump and its attendant losses."
The wet clutch DCT simply takes power to run. It is a physical impossibility for it to have lower drivetrain losses than the manual. The associated systems just simply will take more power to operate. It is impossible for a wet clutch DCT to have the drivetrain efficiency of a manual but the difference is not huge. DCT's often have higher mpg ratings due to having a 7th gear not due to lower losses. They have quicker acceleration figures due to the tighter gearing and shift speed.
We thought it would be best to not have you take our word for it but research the topic and have the experts in the field provide their thoughts. Who knows this transmission better than the manufacturers themselves and the people who work on them? BimmerBoost started by contacting Getrag who makes the DCT transmission in the M3 and asked about the drivetrain losses compared to the manual:
Getrag states that the hydraulic systems drain a bit of power. Ok, well, how about another manufacturer, what would Borg Warner think on the subject?
Well, it seems that both major manufacturers are in complete agreement on the subject. What about tuners who modify these vehicles, what would they have to say? I contacted AMS with the same question:
Hmmm, ok, what about a company that specializes in aftermarket DCT's? Here is what South Side Performance had to say:
Well, it would seem we are seeing a pattern here. What about the website dctfacts.com? They specialize in DCT information and news, here is their take on the subject:
Well, it would seem the entire industry is in compete agreement. Now, the penalty for the DCT's added systems is not large, only about 2%. However, as you add power it does become noticeable. Here is a practical example with 2 supercharged M3's both running the same SC, same boost, same fuel, on the same dyno. The red is manual the blue is DCT:
The best run vs. best run was compared and the difference between the two is just over 3% reflecting the comments of the experts in the DCT industry. So there you have it folks, a little bit of research goes a long way and count on BimmerBoost.com to provide you with the accurate and correct info, not personal politics.