best diff for M30?

[blingsta]

Dont know what diff im using at the moment, but 90mph is at 4.5k rpms in 5th gear !!!!

what is recommended for a better ratio?

[Karan]

e30 m3 3.15

[Rav335uk]

I'd say you,ve got a 4.1 or 4.2 by sounds of it.
I've got a 3.46 on mine which is supposed to be the right one.
But , doesn't it depend on what gearbox you've got, m30 or m40/2

[blingsta]

gearbox is e28 dogleg..

[Rav335uk]

I think johns got the same g/box as you (slowest m30 conversion).Speak to him as he's got a better idea as what to use.

[blingsta]

I think johns got the same g/box as you (slowest m30 conversion).Speak to him as he's got a better idea as what to use.

Whats his username?

[Rav335uk]

http://www.e30zone.net/modules.php?name ... c&t=115721

His name is johnl320 and is using a dogleg box on the link above

[Ziggy]

Isn't the dogleg box 1:1 5th? If so, you'd want a 3.46 or possibly even a 3.15.

I've got a 3.64 with the non-dogleg E28 box, & I've contemplated swapping it to a 3.46 but probably won't.

[blingsta]

i'll start hunting for a e30 m3 diff then ..

[ric325i]

i hope you enjoying that super short diff mine is the same, its fun in some ways but not in others.


for us with the e34 box its like ziggy said 3.64 is the way to go.
it feels like a very different beast!

if your going for the m3 diff im sure you will feel the difference! the way it pulls will put a much bigger smile on your face.

[blingsta]

.. i hope so.. it already feels really strong.. but power runs out to quickly. .. but took it on M25 for the first time and i couldnt believe it when the revs were 4.5k and im only on 90mph.. ..

[ric325i]

that small case isnt the best. you must remember 'doing a gareth' ??? his small case diff only lasted a few hard starts at the pod, then locked both wheels solid. game over.

i dont advise you being too harsh on that little thing with that big lump.

im trying to get my hands on a 3.64 meduim diff for my m30.


with the longer diff you feel the torque for longer, you feel it in your guts. with the small case diff you feel it and then its gone straight away.

i was dissapointed with the m30 with my small case. because you dont feel the torque the engine doesnt feel as strong as it does with a longer diff.

[Rav335uk]

I should be ok then as i've got the 3.46 open mediumcase diff ,

[johnl320]

3.15 diff 70mph at 3086rpm

3.07 diff 70mph at 3008rpm ( this is what I've got)

2.93 diff 70mph at 2870rpm (this is what I want )

my diff will give me 93mph at 4000rpm

HTH

john

[tomson]

Manual E34 535i's have a 3.64 ratio so if you are using the gearbox from one this will be the best ratio, according to BMW anyhow

[Theo]

E34's have a bigger overall rolling radius due to balloon spec tyres, so to get the equivalent gearing on the E30 you would have to either have huuge tyre walls, or a taller ratio diff.

[johnl320]

Manual E34 535i's have a 3.64 ratio so if you are using the gearbox from one this will be the best ratio, according to BMW anyhow

He's not, its an E28 dogleg 1:1 5th gear

john

[blingsta]

3.15 diff 70mph at 3086rpm

3.07 diff 70mph at 3008rpm ( this is what I've got)

2.93 diff 70mph at 2870rpm (this is what I want )

my diff will give me 93mph at 4000rpm

HTH

john

so best would be a 2.93 then! .. which models do these diffs come from ?

[blingsta]

ive got the opportunity of getting a 3.64 LSD.. would that be better than what i already have?

[johnl320]

2.93 and 3.07 both come from E28 525e. Earlier ones had the 2.93

HTH
john

[johnl320]

ive got the opportunity of getting a 3.64 LSD.. would that be better than what i already have?

3.64 will give you 70mph at 3566rpm

128mph at 6500rpm

hth
john

[Rav335uk]

John, what will 3.46 give, bearing int mind, i'm using the 535 manual box, and 16" alpinas with 205 x 50 x 16 tyres?????

[johnl320]

I think your fifth gear is an over drive so 0.81 in 1 out. Someone correct me if I'm wrong.

If so results will be

70mph at 2724 rpm

167mph at 6500rpm

In my opinion thats perfect for this conversion, proper cruiser but it will still be very lively

john

[Rav335uk]

[nickso]

i had 3.46 lsd on mine (pictonroad has it now) it was pretty good with that in it. 2nd and 3rd were fabulous

[johnl320]

Sorry, heavily edited, Misread your PM. a 2.91 is ideal

HTH
john