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:
As there is a pump in hydraulic actuated DCTs the loss of the DCT in principle is a bit higher compared to a manual transmission.
Mit freundlichen Grüßen/ Kind regards
Dr.-Ing. Hartmut Faust
Chefingenieur Entwicklung Zentralbereiche
Vice President Central PD Functions
Getriebe- und Zahnradfabrik
Hermann Hagenmeyer GmbH & Cie KG
Fon +49 (0) 71 31.644-45 10 | internal: 45 10
Mobile +49 (0)178.6 000 415
From a pure physics perspective, the manual transmission is more mechanically efficient, all other factors (number of gears, ratios) being the same. The DCT must have a control system to operate and that requires either an engine driven hydraulic pump similar to a conventional automatic, an electrically driven hydraulic pump, or electrically driven motors and servos. So, some energy must be consumed to automate the DCT... approximately 2% fuel efficiency penalty for engine driven pump and an oil bath pump, only about 1% for electrically driven system and a dry dual clutch (examples are VW DQ200 sold in Europe and China, Ford's new Powershift built by Getrag, Fiat C635 just introduced in Europe).
BorgWarner Drivetrain Systems
3800 Automation Avenue
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West Chicago, IL 60185
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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.