Turbo M52 Diff Ratio

[crazymonk]

Hi everyone, I'm using the M52 engine, (I think thats right, it's the 2.5L 24v non-vanos engine), for a base for my turbo conversion for my E30 Cab. I've got a lot done to the engine, but I'm abit stuck on the diff. I'm using the 6 speed gearbox from a 1998 E36 M3 Evo, but I'm not sure what diff ratio to use. I've been looking at which LSD to get, but there are so many different ratios available, I've seen ones ranging from 4.1 to 2.79. I was originally looking at a 3.9, but I've been told a 3.73 would work better. I should be running around 350hp, I don't want it too high as the cars used daily, and often taken on long trips away, so I need this reflected, but I want it to be quick at the same time. Would using a diff for an E30 be best, or would I be best off using the diff from the E36 M3 Evo I got the gearbox from?

[Andy325i]

you need a high ratio diff simular to an E36 M3, but in the right casing so something like an M coupe diff. The right raito will be around 2.93 - 3.15(?) Anything like a 3.73 will give good acceleration but will become annoying very quickly! I had a 4.10 in my M52 conversion for a while, and while great fun, overall it didn't feel much quicker as I was always changing gear! Top speed was 110 MPH flat out (private road of course!) Currently it runs a 3.38 ratio and this gives a nice balance.

Hth

Andy

[dasparkybad]

I have a 3.08 diff from an e28 525e in mine running an m52 2.8 with the correct 2.8 gearbox this gives me just over 60 mph in second gear at rev limit have not got lsd yet but when i finally get one i will be building it around this ratio as i am very happy with how it makes my car drive

[DanThe]

60 mph indicated or 60 mph gps measured?
I get 60 in second with my 3.25 M3 diff, but this is with the rev limit raised and at approx 7,000 rpm

Some of the E46 diffs are a 3.07 ratio and would be ideal if the CW/P could be donated

[Andy325i]

Do the E46 CW/P bolt in then Dan?

[DanThe]

Ive no idea Andy, CW's are the same size though, 188 mm

I won one on eBay a few months ago for 99p, but the nobber decided to get clever and told me there was an error in the listing and it was meant to be a diff 'carrier' not the diff itself even though a diff was pictured, even gave me the big bull5hit story about how the diff was 'broken up inside' which is why it couldnt be sold

[mcnrss]

Does any of know where id get a diff around 3.25 od 3.07 for my e30 conversion i believe a e28 m535 is too large a casing for the job?
thanks russell

[Andy325i]

Does any of know where id get a diff around 3.25 od 3.07 for my e30 conversion i believe a e28 m535 is too large a casing for the job?
thanks russell

Hi Russell, the 3.25 is an E30 M3 ratio (not sure if its normal E30 M3 or sport Evo, iirc one was 3.15 and one was 3.25)

As you say some of the E28 diffs are 3.07 and I think this is available in Medium size caseings, for example from an E28 525e? (same size as a E30 325i), but the larger M535i Diff WON'T fit without MAJOR mods as the case mounts are different! I know, I've been here

An E36 325i(manual) is 3.15
and an E36 328i (manual) used 2.98

Both of the above E36 diffs can be built into E30 casings (apparently) but E36 LSD are rare as rocking horse sh*t.

Hope this helps

Andy

[mcnrss]

many thanks mate for the help!

[DanThe]

If I was going turbo I would defo choose a ratio under 3:1 as the gears would just not last long enough

[Gunni]

what are the transes ratios?
how much power?

Also tire size and max rpm

[tomson]

Does any of know where id get a diff around 3.25 od 3.07 for my e30 conversion i believe a e28 m535 is too large a casing for the job?
thanks russell

I have a 2.9:1 open diff available, from an E28 525e. All it needs is the back plate from an E30 large case diff to make it fit.

PM me if you are still in need