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M4 DCT flywheel in 335is

Discussion in 'BMW DCT - GS7D36SG' started by BMWJunkie, Dec 25, 2016.

  1. BMWJunkie

    BMWJunkie Lurker

    Its the giving season right? I encourage everyone to share information instead of keeping good info secret, this helps progress the platform. I could of very well kept this to myself and gone faster and no one would of been the wiser. Happy Holidays from BMWJunkie!

    The Idea:

    I have been working on David Rooney's 135i DCT swap for awhile now. I am very familiar with the look of and weight of the n54 DCT flywheel. While reading about a clutch upgrade on a f80/82 I noticed a picture of the flywheel in the m3/m4 and it looked much different and much lighter. I was curious and used realoem to inspect weights of the two. The difference was huge. The m4 part rang in at 8.1kg and the stock 335is unit was a whopping 12.92kg! I verified they both used the same bolts, same bolt pattern, thread pitch, and same clutch pack. On paper everything looked great. Located a used m4 dct flywheel from a junk yard and the project was on.

    The Swap:

    When the m4 unit arrived I could immediately tell it was a much lighter unit. I verified the splines on the clutch pack were the same and test fitted it onto the crank of a n54 I happened to have in the garage. Everything looked as expected.

    I pulled the trans out of my 335is and removed the DCT flywheel. The side by side shot says it all. The 335is flywheel is a typical bmw dual mass flywheel and the m4 unit while still listed as a dual mass did not have any noticeable play in it or even look like it was dual mass. It could be dampened internally but I could not be certain.

    IMG_20161224_120920.jpg IMG_20161224_121025.jpg IMG_20161224_121417.jpg IMG_20161224_121517.jpg IMG_20161224_121546.jpg IMG_20161224_124605.jpg

    As you can see in the photos the weight difference huge 10.5lbs between the two. The flywheel bolted right up. I used new flywheel bolts and torqued to the m4 specifications. The two cars share the same bolts.

    The Results:

    I took before and after free revving videos at roughly the same operating temp and the difference is noticeable.

    The car felt quicker after the upgrade, no more or less than expected. Worth the 300 dollars to me. I am hoping it will help my launches at the drag strip because I've been leaving too hard with the stock flywheel and 5k launch. I am also hoping this is easier on the rest of my driveline.
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  2. BMWJunkie

    BMWJunkie Lurker

    Not sure but if I had to guess they wanted the non m cars to feel very smooth like an auto. The m cars are suppose to be street legal race cars so they can have a little more noise and vibration.
  3. Nice find!

    Makes me wonder about the possibility of an M4 6MT FW...

    installed in an E92 335i 6MT?!?

    I'm assuming its lighter also. And still retains the "dual mass" function to have at least a semi-quiet idle, unlike most aftermarket lightened SMFW in the E90 6MT's that seem to chatter at idle with the clutch pedal out.
  4. Kish2604

    Kish2604 New Member

    Excellent write up! Thank you for sharing this valuable information with us dct guys, now to find an M4 flywheel....
  5. andym3100k

    andym3100k New Member

    Did you test out whether any much faster for 1/4 mile or a 100-200 timing?
  6. Torgus

    Torgus Corporal

    For launching doesn't a flywheel with more mass help? Obviously to a degree.

    For instance you wouldn't want a 1lb flywheel right?

    Curious what the optimal flywheel weight is to hp/tq.

    Cool find that it fits and is lighter!
  7. BMWJunkie

    BMWJunkie Lurker

    I have not gone to the track yet but plan on doing so. I feel like the M4 DCT flywheel is the correct weight for drag racing simply because they're putting a better 60-foot times then 335IS cars
  8. andym3100k

    andym3100k New Member

    Sounds good, can't wait to see your results.
  9. Looking at the photo, the flywheel and starter ring look the same. The IS has an extra weight ring riveted to the flywheel. Now that you have a spare, why not drill the rivets and see if you can pull the 10.5lb ring off the flywheel. If so, it might save people from trying to find an M flywheel if they want to do this mod.
  10. artsoasis

    artsoasis Lurker

    Has anyone tried removing the ring?
  11. BMWJunkie

    BMWJunkie Lurker

    Removing the ring would also remove the splined section that connects to the transmission.
  12. I disagree. If you look at the picture, you can see they added a weight to the DMFW. Only question, can you remove it without damaging the DMFW. From the picture, it looks as if there are only two pins holding the weight. Without having one in hand and taking it apart would you actually know.

    Any chance you can drill the two pins out considering you don't actually need it anymore?
  13. Omar@VaderSolutions

    [email protected] Sergeant Vendor

    NY & AZ
    N54 135i & N54 335i
    where do you see the rivets ?
  14. dyezak

    dyezak Lieutenant

    Plano TX
    They are easiest to see in this image and on the flywheel on the left (S55). Radially aligned with each bolt hole for bolting the flywheel to the crankshaft you will see a bronze colored rivet. Now looking at the flywheel on the right you can see how those rivets (recessed on the N54/N55) are holding the weight on.

    Someone on N54tech.com did remove the rivets (I think it may have been Pure Turbos). They said it most definitely removed the splined section.