M4 DCT flywheel in 335is

BMWJunkie

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Dec 25, 2016
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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.

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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.
 

BMWJunkie

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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.
 
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Nov 8, 2016
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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.
 

Torgus

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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!
 

BMWJunkie

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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
 
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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.

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.
 
Removing the ring would also remove the splined section that connects to the transmission.
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?
 

Omar@VaderSolutions

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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.
where do you see the rivets ?
 

dyezak

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where do you see the rivets ?

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.

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Asbjorn

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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.

I just installed the M4 DCT flywheel in my Z4 N54 DCT. It feels great, but I get some additional vibration at low rpm under load. For instance when it shifts into 7th during slow acceleration uphill in D. Is this normal? I do not remember the M4 doing this.
 
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mrgasoline

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Apr 14, 2023
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I just installed the M4 DCT flywheel in my Z4 N54 DCT. It feels great, but I get some additional vibration at low rpm under load. For instance when it shifts into 7th during slow acceleration uphill in D. Is this normal? I do not remember the M4 doing this.
Do you have any feedback on this? Considering the same update on my Z4 N54 DCT and having doubts... xHP is looking like a solution to set the rpm range on the gears for possible low RPM vibrations. Any chatter or discomfort? Would you state the benefits and challenges?
 

Asbjorn

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Do you have any feedback on this? Considering the same update on my Z4 N54 DCT and having doubts... xHP is looking like a solution to set the rpm range on the gears for possible low RPM vibrations. Any chatter or discomfort? Would you state the benefits and challenges?
Hm no, not really. Still not sure if this issue is specific to the flywheel I got. I am running a custom DCT tune + raised idle rpm, similar to what you described (thanks @carabuser). This completely eliminated the issue. I had actually forgotten I am running a lighter flywheel. God the amount of mods on this car...

Anyway, I have had no other issues. My mechanic says it's a bit noisy when the car is idling and he is under the car, but I don't notice it from the drivers seat.

As for benefits, it just makes the car rev a bit more freely. If you come off the throttle in gear it also engine brakes a bit harder. It shifts the personality of the car a bit towards racecar.
 

mrgasoline

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Apr 14, 2023
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Excellent feedback @Asbjorn , will be upgrading to M4 flywheel in few weeks. Could you also tell more about your custom tune? xHP flash or MHD Z4 35is or both? Also NVH drives me crazy but willing to give it a shot since I mostly use it for spirited driving...

Current mods to share with forum;

Vehicle: 2010 Z4 35i Orion Silver
Öhlins Road & Track (Replaced instead of ST XA due to harshness)
VRSF Inlet - Charge Pipe (Outlet also in stock but not upgraded yet, OEM Turbos are nightmare to install due to diameter)
Index 12 Injectors
Secondary set of cats removed - no downpipes
AAF Oil Pan Baffle
Mosselman Thermostat
Turner Baffled Oil Catch Can
''Mickey Mouse'' ECS Billet Cylinder Head Outlet Hose Adapter
Heavy Duty Aluminum Bleeder Screw
PCV Valve Upgraded Replacement
M4 Flywheel (in a week)

To be upgraded;
MHD Software Update & DCT Tune xHP
Wavetrac LSD
F80-82 Front brakes and pads // or possible recommendations for front & back.
 

Asbjorn

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Mar 10, 2018
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Z4 N54 DCT
Excellent feedback @Asbjorn , will be upgrading to M4 flywheel in few weeks. Could you also tell more about your custom tune? xHP flash or MHD Z4 35is or both? Also NVH drives me crazy but willing to give it a shot since I mostly use it for spirited driving...

The only NVH I had was in high gears at low rpm and under load. A typical scenario would be uphill in D+normal mode at 70km/h. You can solve it with an xHP flash tune, setting the upshift points a bit higher for the higher gears. That's it. My custom tune essentially does the same plus some other unrelated stuff that I barely remember anymore. It just works.

I forget if I also had to increase the idle RPM due to the flywheel or if I only did that because of the VTT engine mount inserts I run. Might have only done that because of the latter. Anyhow the idle rpm can be set in MHD. If you dont like NVH, then dont touch the engine or DCT mounts.

Excellent feedback @Asbjorn , will be upgrading to M4 flywheel in few weeks. Could you also tell more about your custom tune? xHP flash or MHD Z4 35is or both? Also NVH drives me crazy but willing to give it a shot since I mostly use it for spirited driving...

Current mods to share with forum;

Vehicle: 2010 Z4 35i Orion Silver
AAF Oil Pan Baffle
Mosselman Thermostat
Turner Baffled Oil Catch Can

To be upgraded;
MHD Software Update & DCT Tune xHP
Wavetrac LSD
F80-82 Front brakes and pads // or possible recommendations for front & back.

So here's what I can tell you:
1) The AFF Oil Pan Baffle doesn't do anything. I have tried several oil pan baffle "solutions", tested on track with oil pressure logging etc. I know exactly what the problem is with the N54 and none of them work. It is evident from the AAF website describing the product that they don't know what the problem was or how the baffle solved it. Because its mainly related to braking and left hand turns.
Look at the S55 design (or M-version of N55) for an idea of how it can be solved. Unfortunately the tech does not transfer to N54. Accept it and dont take the car on track with grippy tires. Same problem for the 1M - not built for racing like the S55.

2) I dont understand why you run a non-OEM oil thermostat. Take it from someone who has tried several different oil coolers, adding additional oil cooling with an electric pump to the oil sump, as well as entirely bypassing the oil thermostat. Just use the OEM setup and dont worry about it.

3) I also dont understand why you run an oil catch can. It probably wont catch anything. Dirty valves is just part of N54 life. I took mine off after a year or so.

4) Probably cant go wrong with MDH and xHP.

5) An LSD is nice but waay too expensive. Not worth it at all unless you want to practice drifting. The Z4 is really hard to drift though. High center of gravity etc. An LSD feels great on the track, but please just don't. Waste of money for street use.

6) Also don't change the front brakes man. Just don't. You might mess up the brake bias and end up with a longer brake distance. If the caliper piston area is larger than stock you also end up with a longer brake pedal. No good. Best case scenario you get the same short braking distance as stock, with a car that looks worse than before because the front and rear brake calipers do not match.

It's an orion silver car. Keep it classy. Keep it stock. Or go all in like I did and waste a ton of money for absolutely no benefit on the street other than looks.

If you want a different brake pedal feel, just swap the pads. You can get harder track oriented pads that bite harder and just install them in the OEM calipers. Just remember to swap both front and rear so as to not alter the brake bias. But know that you then typically end up with more brake noise, rotor wear and dust... and you may loose braking power when its cold depending on how extreme you go.

If you just want shorter braking distance, all you need is better tires. Thats it.
 
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