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    • E92/E9X M3 Drivetrain Losses Explained - DCT (dual clutch transmission) vs. Manual

      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:

      Thanks for your question and for your interest in our products.

      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

      GETRAG
      Getriebe- und Zahnradfabrik
      Hermann Hagenmeyer GmbH & Cie KG
      GETRAG InnovationsCenter
      Hermann-Hagenmeyer-Straße
      74199 Untergruppenbach

      Fon +49 (0) 71 31.644-45 10 | internal: 45 10
      Mobile +49 (0)178.6 000 415
      Hartmut.Faust@getrag.de
      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?

      Good question, and the answer, as with so many engineering / human interface questions is... it depends.

      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).

      Bob Blakely
      Director, Marketing
      BorgWarner Drivetrain Systems
      3800 Automation Avenue
      Auburn Hills, MI 48326
      Phone: 248-754-0257
      Fax: 248-754-9257
      Cell: 248-330-2585
      bblakely@borgwarner.com
      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:

      Dual clutch takes more power to run.

      Chris Black
      --Tuner--
      Automotosport, Inc.
      1760 Metoyer Court
      West Chicago, IL 60185
      (847) 709-0530 ext. 2014
      www.amsperformance.com
      Hmmm, ok, what about a company that specializes in aftermarket DCT's? Here is what South Side Performance had to say:

      We see a penalty of about 2% compared to a manual. The accepted standard for a manual is 15% so we would say a RWD DCT is at around 17%. AWD DCT's would be slightly higher.

      Kris@SSP
      http://www.sspperformance.com
      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:

      In terms of mechanical efficiency, a dual clutch transmission will never quite be able to match the theoretical efficiency of a standard six-speed manual transmission, as the necessary hydraulic systems will inevitably absorb some energy, especially on a wet clutch DCT. Manuals have no such systems.

      http://www.dctfacts.com/information/...ion-works.aspx
      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.

      This article was originally published in forum thread: E92/E9X M3 Drivetrain Losses Explained - DCT (dual clutch transmission) vs. Manual started by Sticky View original post