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Gents, I will be shortly conducting a differential change on the euro 3.6 and would like some input from those who have done it or experienced such things. Or indeed have the knowledge to comment.

In previous bimmers i have on 2 seperate ocassions gone from a 3.23 to 4.11 and what a difference. Although be it not in a performance vehicle.

Anyway what i want is experience input. Running on 255's and current final drive is 3.91 (im pretty sure). I will be purchasing a NEW center and casing, in other words complete unit including LSD unit, surprisingly not that expensive. Options are 4.10,4.27,4.45 and 4.75. Im thinking going extreme, why not? :) worse case i can easily always go back to original, in fact i can and have had this diff in and out in under an hour, very simple job.

Those experienced guys, share some thoughts, what improvements could someone realistically expect (aside from being underivable in the wet) down a 1/4 mile, top speeds 0-60 etc. What else to consider. The car never see's HWY miles and is parked up for 27 of 28 days a month.
 

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1995 BMW M5 Touring Individual Orinoco over Petrol Mint
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0-60 and 1/4 mile will depend on gear shifts. If you need to shift to 3rd to reach 60 then it will highly affect your times.
The same goes for the 1/4 mile, you'll want to hit the distance right before redline in 3rd.

This will help you, replace the numbers with the correct gear ratios.
 

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You can test to a certain extent by changing wheel sizes. If you put on some 15" 225/50's , it will be similar to having a 4.1 (from a 3.91). I'm doing some back to back testing on 18th March with 15" vs 17" with the 3.91

Would be really interested to know what prices you can get for those ratio's - I've tried various routes to change to 4.1 and short of buying complete Quaife internals, it's looking like c. £550 for BMW Motorsport Crownwheel & Pinion. I thought I'd got it sorted with a 4.1 CWP from a 730i but it turned out that BMW put 188mm internals inside a large case diff !!!
 

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only problem with 15's Julian , is they won't clear standard M5 brakes .

How's testing for the forthcoming season going ?
 

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Ah, yes, that might be a problem :) I'd forgotten the AP's were more compact than the Std calipers.

Testing has so far consisted of opening the garage and testing my eyes to check she's still there. Need to get my head in the right place now as only 3 weeks until the season opener at the new Snetterton 300 - being lazy, I'm only testing the day beforehand.
 

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Some things never change Julian ( That was my post re the brakes above , from Steve's ID ) .

I think I'll pop up Snetterton on March 19th to see how you get on !

D
 
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