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  #1  
Old 13-01-2020, 11:31 AM
SammyZ3M SammyZ3M is offline
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Default Diff upgrade options?

Hi pretty new to z3m coupes, as far as I know they are an e30 style rear diff? 188mm medium case? What options have I got with upgrading to a 3.7/3.9/4.1
Can I just use an e20 LsD or are they not up to the job? Has anyone else had a lsd built into there original z3m casing?

Cheers
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Old 13-01-2020, 12:11 PM
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Quote:
Originally Posted by SammyZ3M View Post
Hi pretty new to z3m coupes, as far as I know they are an e30 style rear diff? 188mm medium case? What options have I got with upgrading to a 3.7/3.9/4.1
Can I just use an e20 LsD or are they not up to the job? Has anyone else had a lsd built into there original z3m casing?

Cheers
Yes it's E30 medium case.

Stock ratio is 3:15 which I found too tall. I've tried an E30 sport 3:64 diff which I found too short so then I found the Goldilocks ratio of 3:46. Perfect!

JC Racing at Thirsk will build a good BMW diff in a stock case or you can buy Quaife for Z3M. I'm sure there are others too.
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Old 13-01-2020, 01:15 PM
SammyZ3M SammyZ3M is offline
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Thanks mate I was thinking of a 3.7 or 3.9 to be honest! Would I be alright with just using an e30 LSD. Will they bolt straight in?
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Old 13-01-2020, 01:22 PM
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Yep, straight swap.
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Old 13-01-2020, 01:29 PM
SammyZ3M SammyZ3M is offline
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Cheers. What sort of revs are you pulling in 5th?
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Old 13-01-2020, 11:19 PM
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c_w c_w is offline
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3.64 lsd is quite common from e30s, but they're all about 35yrs old so may need rebuild.

Z3m lsd is stronger but ive had no issues running an e30 derived 3.46 lsd on my car for about 10yrs. Just need output shafts and backplate swapping. 70mph = 3300rpm (3000rpm stock 3.15). For mainly track 3.64 should be ok. 1st gear will be very short.

2.2 and 3.0 sport z3s use 3.38 and 3.46 torsen lsd but clutch pack m style felt better to me.
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Old 14-01-2020, 08:10 AM
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My car is LS powered with a six speed Tremec so there’s no valid comparison for you as the ratios are obviously different.

If you do a search this has been discussed a fair bit on here before and I know that 3:46 is considered a sweet spot with an OEM five speed box too.
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Old 14-01-2020, 08:16 AM
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I’ve just read c-w’s reply and I would add that I ran an E30 LSD in 3:46 with nearly 400rwhp for 10000 miles with no problems when my car was LS1 powered.

I’m back to the OEM 3:15 now with the bigger power LS3......we’ll see how it goes.
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Old 14-01-2020, 03:32 PM
SammyZ3M SammyZ3M is offline
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Cool cheers guys, I’ve found an open diff from an e30 3.9 ratio. Would it best to use the gear set out of this and get it built into my z3m LSD/ casing & maybe get the ramp angles changed if I fancy it locking abit more?
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Old 14-01-2020, 04:10 PM
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What are you using the car for? 3:9 would be very short.
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