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      10-03-2021, 11:32 PM   #1
eggman51
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Swap stock 2006 Z4M diff for freshly rebuilt 2001 E46 M3 diff w 4.10?

Would you swap a stock 2006 Z4M diff for a freshly rebuilt 2001 E46 M3 diff w 4.10 final drive ratio?

A mate is parting out his E46 M3. The diff is from a 2001 E46 M3. It has <3000 km on it since a fresh rebuild when he swapped in the BMW motorsports 4.10 gearing.

My 2006 Z4M is driven more on the track than the street. I plan to do a 4.10 final drive ratio at some point. Using this diff will likely be half the cost of what I was planning to do. My plan was to do a diffsonline 3 clutch limited-slip diff, which will be significantly more expensive.

I understand there are differences between the E46 M3 diff and the Z4M diff. If I understand correctly, the Z4M diff is "superior" to the E46 diff, particularly the earlier E46 M3 diffs (the one I can get is an earlier model).

Does anyone know if these differences are material to track performance?

What are your thoughts on this swap for a car that is mostly driven on the track?
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      10-04-2021, 12:54 PM   #2
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      10-04-2021, 01:11 PM   #3
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Quote:
Originally Posted by Vanne View Post
Does the thumbs up mean you would do the swap of a 2001 E46 M3 freshly rebuilt 4.10 diff with the stock 2006 E85 Z4M diff with a 3.62 drive ratio and 100,000 kms?
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      10-04-2021, 02:27 PM   #4
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Quote:
Originally Posted by eggman51 View Post
Does the thumbs up mean you would do the swap of a 2001 E46 M3 freshly rebuilt 4.10 diff with the stock 2006 E85 Z4M diff with a 3.62 drive ratio and 100,000 kms?

The LSD unit in the Z4M (same unit as the e9x m3/e60 m5 LSD) is different then the e46 m3 unit. IIRC it has more clutches then the E46 m3 unit but is harder to rebuild due to needing a "key" to open up the LSD. The e46 m3 unit is quite easy to rebuild with parts from racingdiff.com.
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      10-04-2021, 09:55 PM   #5
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More clutches should mean better diff afaik, but does anyone know if the difference between an E46 M3 diff vs an E85 Z4M diff is noticeable on track?

Cheers!
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      10-05-2021, 05:31 AM   #6
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No, the popcorn means I wonder what you will do.. if it were me, I'd buy the proper race diff and add the 4.1's, and do it right the first time. Unless your Arton Senna, there would be zero noticble differences between those two BMW diffs. A racing diff however, complete game changer, setup for your track and drive style..
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      10-05-2021, 05:50 AM   #7
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The difference between the E46 and Z4M diff will be minimal on track compared to the difference the 4:10 gearing will make. Since both are clutch type, they will behave similarly. And the clutch style diff is meant for track use. The Z4M was just slightly more aggressive in how quickly it locked up. The clutch style diff is better suited for low grip surfaces or if a wheel lifts mid-corner but isn't as predictable as a torsen style diff you would see on a Miata.
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      10-05-2021, 11:07 PM   #8
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Quote:
Originally Posted by eggman51 View Post
Would you swap a stock 2006 Z4M diff for a freshly rebuilt 2001 E46 M3 diff w 4.10 final drive ratio?

Does anyone know if these differences are material to track performance?

What are your thoughts on this swap for a car that is mostly driven on the track?
Will 4.10 final drive be a good fit for the tracks you wanna drive, will it allow you to be in optimal rev range for corner exit? That's literally the only question you need to consider.

BMW OEM diffs IMO are made to be a compromise between good track capability and good street manners, so going from a Z4M to an M3 diff is more of a lateral move vs. going to OS Giken / ATS Carbon setup. I run ATS and it might as well be magic in mid-corner and corner exit traction, as well as wet conditions vs how the OEM diff was. The tradeoff is a bit of noise and frequent fluid changes.
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      10-06-2021, 09:22 AM   #9
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Quote:
Originally Posted by bwright657 View Post
The difference between the E46 and Z4M diff will be minimal on track compared to the difference the 4:10 gearing will make. Since both are clutch type, they will behave similarly. And the clutch style diff is meant for track use.
Both the z4m and e46 M3 don't have 'clutch style LSD's'

Yes they do have a clutch pack, but a 'clutch style LSD' as referred to in the colloquial language is a 'Salisbury' or 'Ramp style' LSD, whereas the diff in the Z4m and E46 M3 is a 'gerotor pump' style LSD (although it doesn't have a gerotor pump but that's another discussion)

The gerotor pump LSD and ramp style LSD have completely different fundamental workings.
The ramp style LSD is torque actuated whereas the gerotor pump LSD is speed differential actuated. So how and when they lock up differ greatly.
The gerotor pump LSD only locks up if it sees a speed difference between the left and right axle, so for instance when one wheel slips.
The ramp style LSD locks up the moment when power is applied. So when you open the throttle. The more throttle you give, the more it locks up.
This is the type of LSD mostly used in motorsports.
Different ramp angles determine the power of the lock up and whether lockup is also needed under braking.
So for a track car this is I think the best config. Unless driven in the rain maybe.
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      10-06-2021, 11:07 AM   #10
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If you call diffsonline he will say they are completely the same. Now if he's right or not, I don't know. Gave him a call few months ago as I would rather send my unit to be upgraded instead of sending mine as core.
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      10-08-2021, 09:41 AM   #11
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Quote:
Originally Posted by Vanne View Post
No, the popcorn means I wonder what you will do.. if it were me, I'd buy the proper race diff and add the 4.1's, and do it right the first time. Unless your Arton Senna, there would be zero noticble differences between those two BMW diffs. A racing diff however, complete game changer, setup for your track and drive style..
Maybe next Senna…
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      10-08-2021, 11:08 AM   #12
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Quote:
Originally Posted by 3002 tii View Post
Maybe next Senna…
Maybe!
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      10-09-2021, 12:15 PM   #13
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This is great info - thanks!

No Senna aspirations hehe. I'm an old man having a bit of childish fun. That said, I'm doing some time attack and really enjoying it. I figure that through better driving and some thoughtful mods I can go faster.

My upgrade focus for next season is suspension (currently stock) and some aero (none right now). For all the stuff I've done to the car I have tried to go as top shelf on quality as I can afford.

Regards the 4.10 final drive ratio, for all the tracks I visit, there is a section that feels in between 2nd and 3rd. I'm hoping the 4.10 will make that decidedly 3rd. I had planned to do a 3 clutch diff from diffsonline sometime in the future, but then this 4.10 E46 diff opportunity came up.

Based on some research and this thread...

I am going to hold off on the E46 diff and go for a dedicated clutch style diff.

Thanks for the feedback, super helpful to be able to tap into the collective brains of this community.

Cheers,
Eamonn
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