6 Speed Conversion vs. 3.91 Swap

[rjbaren]

I spoke with a Alex at Carma Motorsports in Georgia and he said the Diff swap was the biggest bang for the buck so I did it, and swapped in a 3.15 LSD. I still wanted more so I did the 6speed conversion. The 3.91 and 3.43 may be a little much for the 6 speed, so keep in mind what your next upgrade might be so what you do now will be in harmony with what you might want to do down the road.

[dragon850]

The largest I would go with a manual would be a 3:23 It drives very nice!

What is the donor for 3.23 gears? Thanks

[rjbaren]

Just for edification, with the 3.15 I was turning 3500 rpm at 80 mph and 3750 rpm at 90mph and about 4000 rpm at 100 mph last Wednesday afternoon. I was toying with the idea going up to 110 but backed off, there was a little too much traffic. But she would have done it no problem, that's for sure.

[JDP530]

Would someone please post some photos and identifying marks on a 3.91 LS diff so I can look around salvage yards for one? Thanks,

[8eights]

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What is the donor for 3.23 gears? Thanks

3.23 Euro, E-34-M5 or you can purchase them when I last checked. 2:10mm Diff reference stuff,

2.65... US 850 ONLY?
2.93. E32/E34 V8 4.0 and 850 CSI and E23 745
3.07. E28 M535 and E23 745
3.15 E32 750 and 850
3.23 E34 M5 3.8 6g and E36 Euro M3
3.45. Euro E34 535 and E32 735 and E23 735
3.64 Euro E34 535 E32 735 and US 850 (mabe also US 750 E32 and will be LSD simi rare)
3.73 Euro E32 735 and US E34 M5 and E28 M5
3.91 E34 M5 and Euro 735



@
JDP530

[Fatandre]

I have a 3.15 diff laying in my garage. Would that be ideal with the 6 speed or should I search for a 3.23?
I am running the 2.93 from the CSI now

[dragon850]

[QUOTE=8eights;29830164].

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3.23 Euro, E-34-M5 or you can purchase them when I last checked. 2:10mm Diff reference stuff,

2.65... US 850 ONLY?
2.93. E32/E34 V8 4.0 and 850 CSI and E23 745
3.07. E28 M535 and E23 745
3.15 E32 750 and 850
3.23 E34 M5 3.8 6g and E36 Euro M3
3.45. Euro E34 535 and E32 735 and E23 735
3.64 Euro E34 535 E32 735 and US 850 (mabe also US 750 E32 and will be LSD simi rare)
3.73 Euro E32 735 and US E34 M5 and E28 M5
3.91 E34 M5 and Euro 735

That's right, Nurenburging M5 I knew that... I guess my memory is getting short.

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Would someone please post some photos and identifying marks on a 3.91 LS diff so I can look around salvage yards for one? Thanks,

Chances of you finding one in a junk yard are practically 0. In US there was only one car that came with this diff, for only 1 year 1991. E34 M5, there is only so many of them that got parted and those diffs are long gone.

[Major Cheese]

I have a 3.15 diff laying in my garage. Would that be ideal with the 6 speed or should I search for a 3.23?
I am running the 2.93 from the CSI now

Gary Corcoran and I both run 3.15s in our CSi's. My diff went out on me on the way back to Vegas from a SolCal8 event a few years back. IMO it's a good fit between highway and stop and go. You still have a usable first gear with this setup. Gary had recommended it since I had to replace/rebuild mine. I don't believe that it is worth it ("feeling of" performance wise) to swap out your 2.93 if it's operable.

[rjbaren]

If you swap your 2.93 for a 3.15 LSD then you will be upgrading acceleration performance with the addition of the limited slip.

[Fatandre]

Well, The 2.93 already has a LSD

[rjbaren]

In my 840 the 2.93 or was it 2.91 was open.

[Fatandre]

Mine is from a CSI :P

[ppointer]

In my 840 the 2.93 or was it 2.91 was open.

Hey, wondering if you ever did a write-up on your MT conversion?

[rjbaren]

No, I never did a write up. I used the write up by Terminator on 8er.org. His post or thread is, "From automatic to manual conversion 840" going back to 2012. That should give you everything you need to complete the job. I took my car out yesterday, first run of the year, and got fed up with a soccer mom doing the 45 mph speed limit on a two lane in her Honda Oddesy. I passed her and then hit 95 before I realized, I am a menace to society. Six speed and a 3.15 LSD work very well together.

[TedBobo]

Here's a thread from a forum member:

https://www.bimmerforums.com/forum/s...highlight=olin

[BMWM5LOVER]

My 2 cents.

My 93 J Spec (Euro) with Wokke chips and recently swapped 3.64LSD (from 3:15 Open) is Auto with a 4 speed. I SHOULD have gone for the 3.91. A 3.64 just happened to pop up locally and for a good price. Having it put in turned out to be a nightmare and more costly then the "straight swap" I was told it would be, but that is another story.

My other 8s are a 94 NA Spec CSi and I've briefly driven my Canadan spec 91 6 Speed Manual.

Let me tell you... My 93 is my favourite! These cars were meant to be auto. Yes, the CSi is a blast and an entirely different animal than the regular 8s (manual or auto irrelevant) but I simply would do the 3.91 diff, get the Wokke Chips and blast the autobahn with my 8.
(All mine are V12 variants btw)

[bdiefAZ]

I have the 3.91 in my 93 auto with the Wokke Chips and Dinan Transmission chip. The car is great to drive and the 3.91 offers better acceleration from 0 to 60 over the 3.64. That being said, the car will be converted to 6 speed / 3.15 LSD. I may have been dropped as a child...

[clockwork]

Wow. Have you guys seen the prices for a 3.91 LSD large diff's costs lately? It'd be cheaper to buy a parts vehicle than just the diff. I have a 4 sod auto with 3.64 open diff and am curious if it's worth going to the 3.91 LSD but at todays prices ... My curiosity can wait.

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[TedBobo]

Wow. Have you guys seen the prices for a 3.91 LSD large diff's costs lately? It'd be cheaper to buy a parts vehicle than just the diff. I have a 4 sod auto with 3.64 open diff and am curious if it's worth going to the 3.91 LSD but at todays prices ... My curiosity can wait.

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I noticed that too. It's been about 10yrs since I did the conversion but I believe I paid $600 for the dif.

[clockwork]

TeBobo, was going to the 3.91 LSD from the open 3.64 worth it? Or is it a lot of hassle for little gain?

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[whiteghost1]

TeBobo, was going to the 3.91 LSD from the open 3.64 worth it? Or is it a lot of hassle for little gain?

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Is it worth it? The answer for me was really dependant on your expectations. I really didn’t notice a significant performance increase, so on that note it wasn’t a game changer. But let’s be honest, there isn’t really any options on the V12’s that noticeably increase performance (other than a 3x chipset) that can be done, other than forced/chemical induction unfortunately.

What I did expect was now having an LSD at the end of my right foot, as the primary benefit. The swap itself isn’t complicated and can be done in an afternoon, the only caveat is that these large case LSD’s are as heavy as &@$!, and in that way it can be challenging, especially if you’re doing the job on jack stands.

[clockwork]

Ok that's exactly what I was hoping to hear.
Thanks.

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[JDP530]

I also installed a 3.91 LSD in my '91 4-spd auto last year when I rebuilt the rear suspension. But I also installed the three Wokke chips at the same time. Since the '91 USA model already had a 3.64 gears there wasn't a big difference in gearing. The chips and the 3.91 made a decent improvement in performance, especially with acceleration. There's only 200-250 RPM difference at 80 mph between the two different rear gear sets. I should have done some acceleration measurements from 0 to 60 and 60 to 100 to get a better idea of performance.

[8eights]

The swap itself isn’t complicated and can be done in an afternoon, the only caveat is that these large case LSD’s are as heavy as &@$!, and in that way it can be challenging, especially if you’re doing the job on jack stands.

Did 4 of them that way, The rear carrier doesn't need to come out, Just lossened and tilted, Wiggle the diff on to a floor jack and get it close as possible, Once you get one bolt to grab it's pretty much in.

[TedBobo]

TeBobo, was going to the 3.91 LSD from the open 3.64 worth it? Or is it a lot of hassle for little gain?

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For me, it was worth it. Yes, I do have those famous chips too.