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      04-26-2020, 01:45 PM   #1
eggman51
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Going 4.10 gears - diff options?

My budget has been a bit destroyed with the global pandemic. I have to defer a couple of things, but think I can fit in a 4.10 gearing change.

I will do this through Diffsonline as that is the diff specialist my shop deals with.

My 2006 Z4MR car has 55,000 miles on it. It's a daily driver, but I plan to track it >10 days per year under normal circumstances. I may convert it to a dedicated track car in the medium to far future.

I have thought of:
- ring and pinion only
- Diffsonline 2 clutch diff w tweaked ramps
- Diffsonline 3 clutch diff w tweaked ramps

While I have read about other diff technologies, it seems like the clutch pack diffs are a proven solution for a street / track car.

I'd appreciate any wisdom from this community on LSD / Diff / Differential options.

Cheers,
Eamonn
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      04-30-2020, 07:17 AM   #2
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I have the 3.91 ring and pinion ready to go so like you I have been trying to figure out what to do LSD wise.

Check out Racingdiffs.com as this are my current front runner. They offer a ZF 4 Clutch unit that seems to be pretty popular with the guys over in Europe. I know a couple guys over on M3 Forum are running them and they only had good things to say. They offer fully custom set ups and one option where you can easily change ramps but turning a screw. Even with all the install parts/shipping from the Europe it was still under $1600.

Originally I was going to just rebuild the OEM M Variable LSD with the parts Racingdiffs.com sells but after talking to him there was a change late in production of the diffs in our cars. Prior to this change you could rebuild them but after they changed the design slightly and now you can't rebuild them. This was confirmed by some guys over on the old M3forum.net. From what I remember this same new style M Variable LSD is the same one in the E9x M3. BTW the 3.85 Ring and pinion out of an E9X manual M3 can be used in our diff. Sometimes you can find a whole diff out of one of those for under $500 if someone is looking for a cheap gear set up grade over stock.

The only other option i am looking at is the OS Giken LSD and this is only because it is what Turner Motorsport ran in their E46/E92 Grand-AM cars. They say its the best and if it was their LSD of choice in professional racing then i think this says something. I have read some bad reviews but I wonder if it was due to install.
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      05-02-2020, 03:16 PM   #3
Michael9218
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My track only car has 4.10:1 30/60 ramp from Diffsonline. Dan builds a good diff. I’m running 275 tires. Give Dan a call. Ton of good advice there.
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      05-02-2020, 05:14 PM   #4
eggman51
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Thanks for the feedback Gents.

I spoke with the folks at OS Giken as well as with my Motorsports shop about their units. The beauty of them is they they are extremely tuneable. The worst part about them is that they can require significant fiddling to get right, and can be sensitive to other changes in the car. This is no big deal if you are inspecting the diff in between races, but didn’t seem practical for a DD / HPDE car. I decided against an OS Giken unit for these reasons, but also due to no warranty and very high cost.

The racingdiffs.com stuff looks excellent. One thing that is important is service and support. The shop I am working with is familiar with Dan from diffsonline, so this is a pretty big factor in favour of getting a diff from diffsonline.

I think I will go with a 3 clutch diff set to 35/60. This is what my shop recommends. They know a lot more about this than I do.

I thought about just doing the 4.10 ring and pinion and rebuild the M diff. While it saves some money, I definitely do feel the “variability” in the way the M diff works in track situations. Budget permitting, I will likely do the full 3 clutch 35/60 diff swap when switching to 4.10 gears.

Cheers!
Eamonn aka eggman

Last edited by eggman51; 05-02-2020 at 10:40 PM..
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