LSD - 3.6 or 3.9:1 on 318iS?

Sat Nov 25, 2006 2:56 pm

Appearently, the stock ratio for the 318is diff is 4.1:1. I'm told putting a 3.6 LSD will raise the gearing of the car. Is there a big difference?

Will a 3.6 diff work OK?

Cheers, G

Sat Nov 25, 2006 2:57 pm

it would make the car slower on acceleration but higher top speed.

i don't know if it would work well or not.

Sat Nov 25, 2006 3:03 pm

The standard ratio is 4.10, and ideally is the best ratio. Its low geared due to the lack of torque i believe. A few people have fitted a 3.91 lsd to the car and said that there is harldy a noticable difference, however being a medium case diff and not a smal case diff the prop will need to be shortened etc.

fitting a 3.64 diff will give you a very high top speed but extremely sluggish acceleration and in my opinion would ruin the car and not really be a very useable daily. Iv just fitted a 4.27 lsd (small case so no prop alterations needed) and the acceleration is lightning but it tops out at a lower speed but is bareable on the motorways. It boils down to a choice of what you want, but i would not go any lower than 3.91.

The best diff you can get imho for a 318is is a medium case 4.10 Us e30 m3 diff, they are goldust though.

Sat Nov 25, 2006 3:05 pm

reggiegasket wrote:Appearently, the stock ratio for the 318is diff is 4.1:1. I'm told putting a 3.6 LSD will raise the gearing of the car. Is there a big difference?

Will a 3.6 diff work OK?

Cheers, G

I'm running a 3.64 in my Touring. It was originally fitted with a 4.27.
The only difference I notice is that it's about 10% more economical. I can't say that the performance is noticably different.
It's definately nicer cruising at motorway speeds (700rpm less at 80mph).

Sat Nov 25, 2006 3:35 pm

Thanx for that. My only experience of changing gearing is on motorbikes, where lowering the gearing made the bike feel significantly quicker. I would therfore rather lower the gearing, as I don't do many motorway miles.

Where did the 4.27 LSD come from Dan?

Sat Nov 25, 2006 6:39 pm

they are like golddust too.
I've fitted an open 4.27 to my 318is and my comments are like dans it has transformed the acceleration and top end, who can really take it that far? well we all can but there is plenty of speed on a 4.27!

Sun Nov 26, 2006 12:56 am

4.27 came from a 320 mate, just lucky it was an lsd; LSDs rule by the way. a 4.10 us m3 diff is your best bet, as it also a medium case meaning its much stronger but both these and 4.27 are like goldust.

Went on a motorway run tonight adn was at about 4500 revs doing 85, so only 500ish revs over normal diff. i dont like speeding up past 100 anyway on the m25

Sun Nov 26, 2006 9:26 am

ok thanx

I guess it is possible to compensate a bit with the tyre sizes

Sun Nov 26, 2006 10:05 am

I believe the 318is diff is small case and the 6 cylinder cars have medium case? Is there a problem fitting a medium case LSD on my car? WHy does it need to be a US M3?

Cheers,G

Sun Nov 26, 2006 10:53 am

I'm getting confused here. Small and medium case diffs??
I thought there were only 2 diffs on E30's..... Small and large.

AFAIK, all 325i's and M3's came with large case diffs and all other E30's came with the small case.
Checking on ETK, M3's came with 4.1 diffs if they were USA or Japan spec. All other M3's came with 3.15 or 3.25, all in the larger case.

Sun Nov 26, 2006 2:46 pm

E30s come with small and medium case diffs. Bigger engined 5 series and seven series have large case diffs.
Massive difference in diff ratio between US/Japan M3s and other M3s. Would make them completely different cars.

Sun Nov 26, 2006 2:53 pm

with a 3.64, it may well not even achive a higher top speed, not enough tourque to push it there, so you will have a slower over all car but, more economical on a long run !

Tue Nov 28, 2006 8:58 am

Thanx. My feeling is the 3.64 would be better for long runs, especially as my cars has 14" wheels on right now with 195/60s, which is slightly lower profile than standard - i.e. it's geared down a bit. Also, on the rally I spent a lot of time switching between 2nd and 3rd. A higher 2nd gear might have helped as I could have held onto it more. Also, nailing it in 2nd is a bit hairy without an LSD, especially in the wet. Having said all that, I like the idea of lowering the gearing! And I'll be putting the 15" wheels back on at some point.

Tue Nov 28, 2006 12:02 pm

reggiegasket wrote:Thanx. My feeling is the 3.64 would be better for long runs, especially as my cars has 14" wheels on right now with 195/60s, which is slightly lower profile than standard - i.e. it's geared down a bit. Also, on the rally I spent a lot of time switching between 2nd and 3rd. A higher 2nd gear might have helped as I could have held onto it more. Also, nailing it in 2nd is a bit hairy without an LSD, especially in the wet. Having said all that, I like the idea of lowering the gearing! And I'll be putting the 15" wheels back on at some point.

14/15inch wheels unless the profiles are ridiculous will not make a difference to speed etc at they are the same rolling radius; and 3.54 would bog down 2nd and 3rd gear acceleration like you wouldnt believe; you want a low geared, 4.xx if you want fast acceleration and are not bothered about top speed. a 3.64 would be good on the long runs but would take an our to get to about 60.