3.91 and 3.64 lsd

[m4xos]

i have 2 spare lsd's in my garage,

ones a 3.91 ratio
and the other being a 3.64 ratio

which ones better? the 3.64??

thanks max

[mccarthy]

hi again, think it depends on what you're after.. the 3.64 will give you more top speed i think but the 3.91 better acceleration??

[Rav335uk]

It depends in what your going to put them into, what engine size is the car.
Oh and if their spare mate, i'll have the 3.64 cheers

[m4xos]

lol, i want to put 1 in a 318is. ive got exactly 10 people pm me about these diffs, sorry there not for sale people,

[Jon_Bmw]

3,64 would make an iS a total road block. 3,91 if you have to, but ideally you want a 4.1 or higher.

[m4xos]

sod it then, will get kevo to re-con 1 of my 2 broken 318is lsd's i have.
3.91 is now sold £250,
i am keeping the 3.64 for my next 2.5 rally slag.

[ImysE30]

3.64 is a good diff for the M30 conversion

[Jon_Bmw]

Its probably the best plan, you'll have a 'new' diff that will actually lock. You could go higher on the FD too, to make it a bit more zippy by obtaining a 4,27 small case off a touring/cab 318 iirc.

Depends on what you want?

[m4xos]

i just want it even, a good acceleration and a good top end, the diff i got in at the mo is brilliant for top end.
can this be done?

[Jon_Bmw]

You can either have one or the other really, not both. You could muck about and change the 5th gear, but that all gets a bit sad, which is the only way of shortening the acceleration whilst maintaining a cruising gear.

I doubt you can top an iS out with the factory diff in fifth, as I suspect it doesn't have enough power. This is what you mean when you say 'a brilliant top end' right? Or do you mean less revs so better MPG?

[fuzzy]

how much a difference would there be between the 2 diffs? how much would you lose top end or gain in acceleration?

[m4xos]

i think i will stick with top end really, i like sitting behind a few mates in there 325's down the motorway lol,
think i gotta pm kevo to ask prices! anyone know anyone elses that does diff rebuilds?

[m4xos]

i dont know the mathimatical calculations, but between the 2 diffs i have (that actually arent broken) there is definatley a difference, you really notice the acceration on the other one i have.

[Bob_S]

the only way an m42 will hit the lmiter in 5th is if a 24v is pulling it

[bevanbrady]

Just for a definite answer on this, what noticeable difference in the drive will a 3.91 make, as i have a 3.91 lsd here to go into my non lsd IS. I'm taking from this thread it will make the gearing slightly taller on final drive

[m4xos]

yes, according to these zoners!