E28 3.25 LSD into a 318iS

[Mike_z]

Hey guys,
I am a proud owner of a 91' 318is with an S50 stuffed into it.
As fun as those gears may be, it just isn't good when I'm turning 4k at 60mph +-
due to the 4.10 stock LSD it has.

Previous owner included a 3.25 LSD out of an E28 in the sale. I'm aware that in order to get it into an E30 you have to swap out the Diff cover and the Shaft flanges??

What I can't find on the forums is do I swap that out of a diff cover out of a regular 3.25? or out of mine? I think the 318is has a smaller case than the 3.25 i want to put in.

Also what about the flanges? Out of the case in my car? Or do I need to purchase different flanges to install it?

[flyboyx]

there are a jiz load of threads about this already. however, since you are new, to help you along, you will need the flanges and cover from a medium case e30 diff to make this work in your car. replace the seals while you are at it. the parts from your small case are not going to work for you but everything you do need can come from a non lsd diff of any ratio which should cost about 75.00 or less.

[itsonlygeorge]

A 3.73 LSD is a much better ratio for your car. The 4.10 diff was used on automatics and the 3.73 for manuals. The 3.25 is better suited to an 325e with a low redline.

[flyboyx]

he says the engine was swapped to an s50. it depends on personal preference, but 3.73 is probably too low for that application. depending on his needs, highway use would be a bit annoying since there is no over drive with the zf 5 speed.

[itsonlygeorge]

he says the engine was swapped to an s50. 3.73 is probably too low for that application. depending on his needs, highway use would be a bit annoying since there is no over drive with the zf 5 speed.

There's always the 3.64 as well.

[ST1G]

swap diff cover, swap stub shafts. easy.

[24v e30]

he says the engine was swapped to an s50. it depends on personal preference, but 3.73 is probably too low for that application. depending on his needs, highway use would be a bit annoying since there is no over drive with the zf 5 speed.

+1

Stick with the 3.25. That's what I've got in my s52 318i and sometimes I feel like IT'S too short.. but like flyboy said, it's a personal preference.

[straight6pwr]

i had several ratios on my 5 speed 24v swap car, i can tell you from experience the general usefulness of each.
3.73 was too short for a car which was driven on the highway a lot. it would be good for a race car or weekend warrior.
2.93 made the car less fun, but was really good for highway
3.25 was the sweet spot for me, but some may find those rpms even a little high for the freeway. your rev needle will basically 'match' your speedo needle, if you look at them side-by-side. 60mph will be about 3000 rpms, 70 about 3600rpms. if you've driven an m20/5 speed car with 3.73 gears, its almost identical in rpms.

like others have said, sell your 4.10, buy the cheapest non-lsd e30 medium diff you can find, and swap the parts over to the 3.25. you may even pocket some money through all of this. if you decide on a different ratio, the 3.25LSD is very valuable around here as they are getting very hard to come by, so you could easily sell and get what you want instead.

[Mike_z]

Thanks for the replies guys, exactly what I was looking for.
From my previous experiences a 3.73 is still too short, as I had one in my previous 325i.
I'll give this 3.25 a try and paired with the motor I think it'll work out fine. Sad I can't keep this shiny nice cover on it though :(

thank you for the help really appreciate it!