1986 325e Diff swap question

[Shadye30]

Hello everyone.

My name is Freddy and I recently acquired an all stock 1owner 1986 32e 2dr automatic with 82k on the odometer. This is my 2nd E30 (had an E30M3 that I sold a few years back). I'm looking to do a few mods to make it "peppier" around town. I already have a Turner chip installed and will eventually install an "i" head swap and possibly a manual conversion. My next mod that I'm looking to do is a diff swap but not sure what ratio to install 3.25 or 3.73. Any advice? This will be a weekend at best car but don't want it screaming on the highway too much . Thanks in advance.

[Elysian]

3.25 would be a moderate improvement over the (assuming) stock 2.93, 3.73 would be pretty noticeable. Are both options limited slip? If it really is a weekend car I'd go 3.73, but that's just me.

[Shadye30]

Thanks...Yes this would be a weekend car at best during the summer on nice days... What model 3.73 Limited slip should I look for?

[Aleman]

IMO 3.25 is the best ratio for mixed driving. My 325is had a 3.73 from new, but it was really buzzy on the freeway over about 65mph. I like taking long road trips, so I sacrificed acceleration for high-speed comfort, and installed a 2.93 LSD. Now I can do 85 mph quite comfortably, but acceleration has tanked. 3.25 is right in the middle, so I'm thinking that's the best of both worlds. Where might I find a 3.25? I know they weren't put in many 80's-era BMW's...

[Vincenze]

Where might I find a 3.25?

The Z3 M.

[ForcedFirebird]

If the car itself is in good condition. Just do a manual and chip. These cars are worth a lot more (and just all around "better")if they are a gem, than a "racecar".

[Andre3127]

If the car itself is in good condition. Just do a manual and chip. These cars are worth a lot more (and just all around "better")if they are a gem, than a "racecar".

Completely agree. My car started as a stock 62,400 mile 325e, now it's a 62,600 mile car with a full turbocharged 325e driveline on standalone, and I'm going through a ton of extra effort to make it feel like a luxury comfortable car again (what these cars were supposed to be factory). My friends and I are all now adding all the creature comforts back into cars that used to be cool to remove. There's nothing wrong with having a cool, old, comfortable and modest weekend car.

[ADEN]

I don't know my diff ratio no plate no numbers nothing, Running getrag 240 RPM 5th gear at 60 miles is around 2800 stock tires 185/60/14.
Can someone guess my diff ?

[Shadye30]

Would one from a 1998 BMW Z3 1.9L MANUAL TRANSMISSION LIMITED SLIP DIFFERENTIAL 3.45 Ratio work onto my Auto ETA?

[ForcedFirebird]

Would one from a 1998 BMW Z3 1.9L MANUAL TRANSMISSION LIMITED SLIP DIFFERENTIAL 3.45 Ratio work onto my Auto ETA?

Yes. Same diff case/cover, and mounting points. You might need need to swap the axle stubs, pretty sure the z3 used the skinny axles in the 4cyl. I know the 318ti did for sure. The stubs from your diff will work.

[Shadye30]

Thanks ForcedFirebird.

Are you referring to the output flanges on either side of the differential?

Here is a photo of the actual part that I am looking to purchase.

[ForcedFirebird]

That's a small case diff, just an FYI. Most likely to be open too.

[Vincenze]

Would one from a 1998 BMW Z3 1.9L MANUAL TRANSMISSION LIMITED SLIP DIFFERENTIAL 3.45 Ratio work onto my Auto ETA?

I believe only 6-cylinder Z3s had Torsen and clutch LSDs.
You should verify it on Z3 forums.

[Shadye30]

Good catches..thank you both..I have tracked down 2 differentials (both out of 2.5 Z3s) and not sure which one would be better for my street driven auto ETA..3.64 or 3.15..