What Diff in a M30 e34 535 Conversion.

[Black_Op_88]

So I have a M30 535 conversion with a e30 325is LSD. I’m looking to put a fresh differential in her but don't know if it’s best to stick with another sport diff or put something else in its place. They aren’t cheap son I don't want to get it wrong.

Any help would be great.

[Ziggy]

What age 325i is the current diff from?

[staley_turbo]

Anything around a 3.21 is a good start.

[leeparkes]

For a standard M30 a 3.64 is a good choice diff.

[Black_Op_88]

What age 325i is the current diff from?

89/90

[Black_Op_88]

For a standard M30 a 3.64 is a good choice diff.

Yep I was looking at this one http://www.ebay.co.uk/itm/170787895350? ... 500wt_1287

The Diff I have in at the moment is the one that was in the car from production, an 89/90 325i sport diff. Not too sure of its ratio though. I did a search on here for e30 diff ratios but it was telling me there was no such page.

[Ziggy]

What age 325i is the current diff from?

89/90

That'll be a 3.91 then... would make 1st pretty much useless I expect? A 3.64 would be a decent 'improvement' (it's all subjective), if you don't want as big a difference as a 3.46 etc.
Mine's a 3.64 & I can see the argument for a 3.46, especially if you do lots of motorway miles in it, but I'm quite happy with it as is.

[Black_Op_88]

That'll be a 3.91 then... would make 1st pretty much useless I expect? A 3.64 would be a decent 'improvement' (it's all subjective), if you don't want as big a difference as a 3.46 etc.
Mine's a 3.64 & I can see the argument for a 3.46, especially if you do lots of motorway miles in it, but I'm quite happy with it as is.

Yes 1st gear is a real flash in the pan. A part from a better first gear does the 3.64 diff offer any advantages at the top end side of things?

[Ziggy]

Yes 1st gear is a real flash in the pan. A part from a better first gear does the 3.64 diff offer any advantages at the top end side of things?

Lower RPM on the motorway, generally less frantic cog swapping, better economy. Worth noting that you won't get a higher top speed unless it will currently hit the limiter in 5th.

1st is hardly leggy with a 3.64 - I'd be considering that or a 3.46 depending on your priorities. What don't you like about the current diff?

[staley_turbo]

Going by my m535i, I think this had a 3.21 in? This would redline in 5th at around 145mph. (close ratio dogleg)
This is the diff I put in my m30 e30 and am very happy with 1st gear and 5th for the motorways. This is standard ratio 5 speed. I had a 3.91 before this and first was completely useless. The 3.21 put the car back feeling how it should be.

Just checked, the e28 had a 3.07 in. I have a 3.15 from a e28 324td.

[Ziggy]

Going by my m535i, I think this had a 3.21 in? This would redline in 5th at around 145mph. (close ratio dogleg)
This is the diff I put in my m30 e30 and am very happy with 1st gear and 5th for the motorways. This is standard ratio 5 speed. I had a 3.91 before this and first was completely useless. The 3.21 put the car back feeling how it should be.

Just checked, the e28 had a 3.07 in. I have a 3.15 from a e28 324td.

E28 had the 3.07:1 with the non-overdrive dogleg box. 3.25:1 with the overdrive box.

[staley_turbo]

Sorry yes it was the 3.07. I used the 3.15 from the 524td in my e30 and its good.

[Black_Op_88]

1st is hardly leggy with a 3.64 - I'd be considering that or a 3.46 depending on your priorities. What don't you like about the current diff?

I mostly don't like the high rpm even for going about town. Guessing with the higher rpm the car is harsher on fuel. And 1st is a quick getaway of a gear, if you blinked you would miss it.

2nd on the other hand has miles of torque. Which I like. Is 2nd as impressive with a 3.64?

[leeparkes]

A 3.64 is still a beserk diff for an M30, you can easily light the rears in 2nd.

[Rav335uk]

I have a 3.46 on my M30'd Cab, you can use 1st, 2nd no problems, and on the motorway, it "Cruises" very nicely at 100mph on about 3200rpm.

[Black_Op_88]

Well sounds like its a 3.64 for me then . Now I just need a non-abused one

[zaust]

I'm using a 46. I find it good for some rear end action and also good for street and track. But first is still so short that I don't use it.

[Rav335uk]

On a 3.46, you find 1st short????

I find it ok.

[zaust]

I have a sport box. I am able to light the rear

up in 2nd from stand still. When I had the 64 before that it was ridiculous on the road.

[Rav335uk]

That's the difference then Marc, I have a normal 5 speed m30 box.

[johnl320]

I've got m10 gearbox and 3.07diff
70mph = approx 2200 rpm in 5th, proper lazy
First gear very useable though and 2nd will see 72mph approx with standard limiter.

[mr_dink]

3.46 is much rarer than 3.64 AFAIK.

[Rav335uk]

I've got m10 gearbox and 3.07diff
70mph = approx 2200 rpm in 5th, proper lazy
First gear very useable though and 2nd will see 72mph approx with standard limiter.

And I thought mine was lazy on the motorway

[johnl320]

I can drive to work on tickover Rav lol

[zaust]

I would like to try out a 25 ratio. But not easy to find just to try.

[miniblob]

Just to hi-jack this for a minute, (sorry!!) - been thinking (briefly!) about diff ratios for my M20 2.7 with sport box.
Currently running a 3.91 lsd, which is ok, but I find I'm at high revs on the motorway so using plenty of fuel and limiting my top speed!!! Thinking I should maybe try another ratio or two before i empty my wallet with a diff rebuild!!

Am I right in thinking that a lower diff ratio (i.e 3.64) will give me a higher top speed (assuming the power is there!!) and lower revs at the same cruising speed?
Will it also reduce my acceleration times? Noticeably???

I am going to be using this for track days (and it's being mapped properly in a couple of weeks, so I'll know exactly what power I'm playing with then too!!!), but I want to start using it more on the road again too!!!

Apologies again for crashing this thread, but I saw this and thought you guys might be able to advise

[Rav335uk]

I would keep the 3.91 for the track, as that's what you want to keep the powerband up there with.

3.64 will give you less acceleration, and a higher top speed and cruising at less revs, as you've stated.

It's a compromise for you, but why not just swap the diffs over when needed??

[leeparkes]

What about a 3.73?

[miniblob]

Didn't know there was a 3.73!!!

May well just keep the 3.91 then - puts my mind at rest a bit that someone else thinks that and I did research it a bit on here when i originally got the 3.91!!!
Rather take A/B roads anway