What diff would you guys recommend?

[ballin]

hey all,

got an m3 (e36 3.0L) in a 325i Sport.

I believe the 325 diff is a 3.91 ratio is that correct?

Now in 5th gear I'm pulling about 4-4.5k at around 70mph - painful!!

What would you suggest in there, would the m3 diff fit, what ratio is that?

or something else?

[stuartgallafant]

your best bet is to find out the ratio's in your g'box, and try and match them up with that. or, find out the ratio of the diff in the M3 and get as close to that?

bit off topic, but have you seen the guildford thread in the 'meets' section? i noticed you were from guildford. would be good to get another face there

[ballin]

It's the M3 box, so im guessing the M3 diff would be best but not 100% sure!

I've only just got the car but will try and get to some meets probably end up bugging you all with questions

[maxfield]

If you've now got 4k at 70mph with 3.91 diff i'd suggest 3:15 or 3:25

[ballin]

think i need to find out for sure what ive actually got - only going by previous owners!

If it has a standard M3 box, and a standard 325sport diff, then surely it would be revving lower than 4k @ 70mph wouldnt it? i thought the m3 diff was 3.64 or something?

[maxfield]

No E30 M3 diffs were 3:25 and the EVOs were 3:15

[ballin]

e36 m3 mate - 3.0L

[maxfield]

i'm not sure dude but i would recomend 3:25 im sure one of the experts will chime in with what they have used

[stuartgallafant]

saying that, i think the E36 M3 3.0 rear diff is a 3.25. you need to go on somewhere like e36coupe.com and find out

[ballin]

have been trawling the net trying to find out but no joy yet! will try e36coupe cheers fella!

[ballin]

well that was easier!! looks like the 3.0L m3 diff is a 3.15 - no wonder im struggling with a std 325i Sport 3.91 diff!!!!!!

now, will an e36 diff fit ?

[jmc330i]

The E36 M3 diff is 3.25 ratio as standard, with some 3.15s.

You need the E30 M3 diff (3.25 or 3.15 if you can find one) if youre running the E36 M3 5spd box.

now, will an e36 diff fit ?

Not a chance, unless you want a lot of work.

[ballin]

James - all questions answered, many thanks!!!

The hunt begins

[oguz327]

Be good if you could bring your motor down to one of the Guildford meets.

Any pics of you motor dude?

[Stevin]

I'm pretty sure u could transfer the internals from a E36 M3 diff into an E30 diff ?

[ballin]

I will get some pics soon - booked it in to have the exhaust quietened down, it was a powerflow "as loud as poss" exhaust and its awful lol.

especially with the diff ratio goes right through your brain

[ballin]

anybody know any companys in the south that can do custom diffs or anything? dont really want to wait around for a 2nd hand one to become available, im getting about 120 miles to a tank atm

[DieselMeister]

Quaife

[ballin]

Is there a calculation to work out what revs i would be pulling @ say 70mph with different ratios?

Say 3.91 = 4k @ 70mph, can i work out what a 3.45 would pull, and also a 3.25 ?

[Chris-W]

Try this:

[ballin]

Cheers Chris, hoping I can get away with using your 3.45 tbh, as 3.25's are like rocking horse ****!

[Chris-W]

No prob - let me know if you find nothing else, it's a cheap option if all else fails.

[M-technik3]

I use a 3.25lsd from a 535iS in conjunction with a M50 vanos, with S50 cams and a Getrag from a E36 so 1:1 final drive. The rpms on 225-50-15 are comfortable, it's quick off the line but not brutal, a 3.46 lsd would suit it better but I enjoy the fuel savings and the ability that it's flexible thru out the gear box.


Now a EU spec 286 hp 3.0 would runn all day on a 2.93 lsd fine with the added tq and displacement. Being the E30 is roughly 400 lbs lighter than a e36 M the down point is the E36 is more aerodynamic.

[diamondblacke28]

does that mean a diff from a e34 will fit straight in to an e30.

do you think the diff from an e34 518i or 520i. depending on ratios.
would suit an e30 325i as mine is making a noise.

does anyone know the ratios of these diffs.
or poss e36 diff would fit?

as its easier to find e34 parts at a breaker yard in liverpool.

[Chris-W]

I thought the E34 axle was completely different??

[ballin]

From my workings a 3.45 diff will give me 552rpm lower than my current 3.91 @ 70mph
A 3.25 would give 792rpm lower so i think a 3.45 just wont be good enough

[jmc330i]

The E34 diff will not fit the E30 - although it has actually been done by PPF on one of their 900bhp E30s. but its a sh*t load of work.

3.25:1 ratio is the shortest you could really use if your car is an everyday car. The 3.46 would be good for track days

You should be able to find an E30 M3 diff, thats all you need.

[ballin]

doesnt seem to be any around!! but i agree, i think its gonna have to be a 3.25

[M-technik3]

When I mentioned a 535is I was talking about an E28 535iS. Here in the US we got plenty of these.

Surf www.mye28.com A great US site but there are UK members.

[StuBeeDoo]

Is there a calculation to work out what revs i would be pulling @ say 70mph with different ratios?

Say 3.91 = 4k @ 70mph, can i work out what a 3.45 would pull, and also a 3.25 ?

Using 205/55x15 tyres, a 3.91 diff will give you 3850rpm at 70mph.
3.46 gives 3400
3.25 gives 3200
3.15 gives 3100

HTH
Stuart.

[ballin]

Cheers Stuart, I've got 215/40/16 on there atm, I worked it like:

3.91 (diff) x 1.00 (5th gear ratio) x 336) x 70 / 19.6 (wheel diameter?) and got a slightly high calc!

I'm doing around 4.1-3rpm @ 70mph in 5th checked this morning!

[m30e30]

im running a 2.93/1 ratio in mine but the dog leg box is 1 to 1 ratio so i have no top end but hey never mind its a novelty of having a upside downgear box

[StuBeeDoo]

Cheers Stuart, I've got 215/40/16 on there atm, I worked it like:

3.91 (diff) x 1.00 (5th gear ratio) x 336) x 70 / 19.6 (wheel diameter?) and got a slightly high calc!

I'm doing around 4.1-3rpm @ 70mph in 5th checked this morning!

215/40x16 would make the speedo out. By my calculations, they would give you 4000rpm at 70mph. Don't forget that your speedo will be reading approx 5mph fast anyway.
I run 205/55x15's and my speedo reads 74 when Cyclops says 70.

[stuartgallafant]

ballin, your best bet, would be to get a slip diff from the Z3 roadster, which used the S50 lump, g'box and had a slip diff. the rear axle is the same as the the E30, therefore fitting it will be no probs at all.

if you want to know more, speak to adil325i, as he has put one on his E30, and rates it very highly

[ballin]

I got offered a 3.45 from a z3 but i dont think its going to be low enough for mine still, i wonder if the z3 ever had a 3.25 or thereabouts?

essbee, I got the speed off GPS because you are correct, my speedo was quite far out

4k isn't far off, I made a bit of a guess at the wheel diamater because I wasnt exactly sure what 16" with 40 profile tyres equates to!
But anyway regardless, I would like a 1,000 RPM reduction or as close as possible to it, so that would be at least a 3.25 (thats nearly 800rpm i think, good enough!)

Just gotta find one, a custom one is just too much Ԛ£Ã”šÃ‚£Ãƒ”šÃ‚£ at the moment