what diff to use 3.91 or 3.64

[Alex]

What diff should i use with this setup

Car in quesion is a touring with a 325i Engine and 320i Gearbox

Now do i go for a 3.91 Diff or a 3.64 Diff

can you get both as open diffs ?

[Grrrmachine]

The 320i gearbox will give you sport ratios, so I think you'd be better off with the lower diff. That way you'd still have perky acceleration but with a good cruising MPG, which is what you want from a touring

A 3.91 might make 1st gear redundant with that setup.

[Alex]

what are facelift sports like as they have a sport gearbox with 3.91 are they pretty much too revvy through 1st and 2nd

[Ajsingh]

I run a 3.91 with my 2.7 and its great fun! 70mph is 3000rpm on motorway and its great fun around town. Late 325i sports came with 3.91 LSDs so id go for a 3.91. A 3.64 will be great on a motorway run but maybe abit long

Yea both are available LSD and open

I love my second and third gears, the pull is great! And IMO its not too revvy! And it was running a 4.10 diff! Lol

The 3.91 IMO is a good all rounder, offers good off the line speed, fun around town and gives good motorway mpg and keeps the revs low

Edit... My spec is 2.7 engine, 320i gearbox and 3.91 LSD = great car to drive

[Alex]

50/50 so far

[Sanchez]

not any more.

Ive got a touring with 2.5 engine and 2.0 box, current diff is 4.10 open but 3.91 LSD in the garage to be fitted.

Im gona pick up a 3.64 open if one comes for sale cheap enough then i can see whats better for me.

[magpie]

where's the 3.73 option

[e30topless]

3.91 will light up a bit easier but the 3.64 will be better on a cruise/ day to day job,

the 320 box will only give you a higher first and poss second gear the final drive in 5th will be the same as a 325 box IIRC

3.91 were fitted to tech 2's
3.64 were fitted to tech 1's, your going to be running pretty much the same set up as the old sport on this ratio alex

most tourings got a 3.73 which is a very nice all round diff

[Alex]

are 3.73 open diffs easy to get hold of forgot about them

[magpie]

you have 3 months to find one

[Jhonno]

Where's the M50 option..?

[bss325i]

most tourings got a 3.73 which is a very nice all round diff

The standard ratio for a 325i touring is 3.91 auto or manual.

3.73 is the ratio for post sept '87 non sport 325i saloons and cabrios with an auto box.

They are rarer than 3.64 and 3.91 in LSD form.

[bss325i]

Obviously my car runs a 3.91 and driven back to back with 325i's with a 3.64 the acceleration difference is noticable but then so is the fuel economy!

[B7]

What are you going to use the car for mainly. If it's an everydayer then a 3:64. If it's a "hooning about loons tool" then a 3:91.

[Simon13]

a 3.91 is a sh!t diff. 1st is non existant and they're revving their nuts off on the m-way. If you want 22mpg everywhere you go even on a run then fit one.

3.64 no brainer! The difference in acceleration is nothing to write home about, Barry is being picky over 0.3 of a second. The car will drive so much nicer with this ratio plus you'll get some economy when on a run not on a charge

Infact with 3.64 you'll hit 60 in 2nd i expect!

[Andyboy]

325i manual Tourings use a 3.91. Not a bad diff but too revvy for the motorway. I put a 3.64 in mine which made it a lot nicer to drive.

[Dezzy]

my 325i se had a 3.64 when i bought it.

It was the best of both worlds imo.

[Simon13]

auto 325i tourings also use a 3.91

[E30BeemerLad]

3.91 LSD in my chrome turd Alex and it's too revvy on motorways and even driving around town you are doing a lot of cog swapping. I'm usually in 4th gear by 40mph

[B7]

My 2.7 runs a 3:64 LSD and even as an auto, it's still good.

Personally, I think a 3:73 is a good alrounder but theres naff all difference really between the two.

[Ajsingh]

Lol alot of hate against the 3.91

I quite like mine. 3000rpm at 70mph, not quite very revvy as mentioned

What does a 3.64 do at 3000rpm?

[e301988325i]

currently on 3.64, quite tempted to swap for 3.46 TBH

[Alex]

Decision made 3.73 it is

[Sanchez]

Lol alot of hate against the 3.91

I quite like mine. 3000rpm at 70mph, not quite very revvy as mentioned

What does a 3.64 do at 3000rpm?

76.25mph

[Sanchez]

and 3.73 will give 74.41 all with 2.5 sport engine and gearbox in 5th gear.

[Simon13]

Lol alot of hate against the 3.91

I quite like mine. 3000rpm at 70mph, not quite very revvy as mentioned

What does a 3.64 do at 3000rpm?

2500rpm, much nicer how does 3500 at 90 sound? bit better than 4000rpm!

[Dezzy]

I found first gear too short with the 3.64 fitted, whats first like with a 3.91?

[Ajsingh]

Its ok ish i suppose.. I get to about 20mph then gotta change up (anything is better than a 4.10 and 4.27 i used to have)

I redlined once when getting of the line quick and i glanced down and saw 30mph

[Ajsingh]

Lol alot of hate against the 3.91

I quite like mine. 3000rpm at 70mph, not quite very revvy as mentioned

What does a 3.64 do at 3000rpm?

2500rpm, much nicer how does 3500 at 90 sound? bit better than 4000rpm!

Oh wow!

Heres me thinking 3k at 70 is good

[Andyboy]

I restored an early 320i a couple of years ago and that had the original 3.45. It went remarkably well and would do 60 in second just short of the rev limiter.

[e301988325i]

I found first gear too short with the 3.64 fitted, whats first like with a 3.91?

I had the same feeling with 3.64 (open) fitted, fitting a sport c/r gearbox ratios cured first being completely useless, but even now once rolling first is not required, I'd like to swap for an open 3.46.

[pegase747]

3.73 LSD FTW, I just love mine, with 325i Gbox and the C2 engine...

Pierre