Diff ratios

Post Thu Jan 05, 2012 11:54 pm

which diff ratios are people running on the m42 box?

im going to get an lsd and have been offered a 3.73. should i go for that or hold out for a 3.64 or a 3.46?

whats everyone else got and how does it go?

cheers

Post Fri Jan 06, 2012 12:02 am

I guess a 3.73 might be the right compromise for a quick car off the line, and a useable car!

I'm on 3:91, and it's always buzzing

Post Sat Jan 07, 2012 4:55 pm

whats the 3.64 saying boys? anyone got a 3.46?

Post Sat Jan 07, 2012 5:01 pm

Im using a 3:64 and it's spot on as an all rounder,
But I wished id used a 3:91

Post Sat Jan 07, 2012 5:17 pm

craigieeb wrote:Im using a 3:64 and it's spot on as an all rounder,
But I wished id used a 3:91

I'll swap you then

Post Sun Jan 08, 2012 8:10 pm

i got a 3:91 but rev's silly

Post Sun Jan 08, 2012 9:03 pm

Im running a 3:91 on my m52 with m42 box and I find it way to short. Need something a bit longer for a daily car. Fun off the lights though!

Post Mon Jan 09, 2012 5:30 pm

I'm using a 3.64 on my m52 with m42 box...... Imo a 3.91 would make take off quite fun but way to buzzy on duals or motorways!

That said a 3.46 would be to long, with the 3.64 I feel its the best all rounder. Not exactly shy off the line either, and 73-75mph @ 3000rpm. Win win

Post Mon Jan 09, 2012 5:36 pm

Really depends on your driving style/comfort etc.

3.91 if your not too many motorway miles and lower ratio if your around town or like to give it the beans on the strip/track.

Post Fri Jan 13, 2012 8:25 am

My e21 runs an e12 LSD with a 3:07 and standard 323i box. I plan to fit a C/R gearbox eventually but the longer gears haven't made my car any less fun to drive and it has enough grunt to pull hard through each gear. I quite like not having to snatch a gearchange quite so quickly too!

Post Sat Jan 28, 2012 10:38 am

I've got a 320i gearbox on mine not sure what diff i got but at 70mph its around 3400rpm i looking for somthing longer 3.64?

Post Sat Jan 28, 2012 1:25 pm

i have m50 with e36 box and a 4.1 diff ive only test drove down the road and its mental going to try 3.64

Post Sat Jan 28, 2012 1:42 pm

BATTS91 wrote:i have m50 with e36 box and a 4.1 diff ive only test drove down the road and its mental going to try 3.64

I thought that if you use the e36 box you need something closer to a 3.0?

Post Sat Jan 28, 2012 8:39 pm

What was the 3.91 lsd originally be fitted to?

Post Sat Jan 28, 2012 9:47 pm

325i facelift sport

Post Sat Jan 28, 2012 10:08 pm

http://www.realoem.com/bmw/partxref.do? ... &details=1

Post Sun Jan 29, 2012 8:32 pm

Just been playing around with gear ratios here http://www.endtuning.com/gearratios.html

It claims there's 350rpm difference between a 4.10 and 3.64 based on an M42 gearbox @ 70mph, I thought it'd be more than that.
Building a 4.27 LSD seems a bit more realistic now as it looks as though it'll do 3300rpm @ 70mph.

Post Wed Feb 01, 2012 10:48 am

I'm running a 4:1 and was expecting to feel the difference a little more than I do. It does feel better on initial launch but that may simply be that this diff is working better than my old one did?

Post Thu Feb 02, 2012 11:15 pm

BATTS91 wrote:i have m50 with e36 box and a 4.1 diff ive only test drove down the road and its mental going to try 3.64

batts i had that symptom. i had a 4.10 that had no 1st or 2nd. i bought a 3.64 but it was still way ott and had 2nd but no 1st. then i got a 3.08 of danthe and its virtually spot on. its a tad light which makes for good acceleration and still has a decent top end. if you want a factory drive i would recommend a 2.93. i wouldnt bother with a 3.64 for a road car on an e36 box, better on a track really.