Pondering E36 M3 Evo diff

Tony its funny I also have a 3.91:1 M5 dif in mine which I fitted having read some glowing reports about the benefit etc. (M70 engine auto box) and like you to date I am very happy with it. I too also have the old dif if required but for now its all good

Sorry mates, I think I said it all wrong!

I do not mean that costumizing one's car is a bad thing! No way! It is a great thing.
It is my hobby, too! And putting in a different diff (or radio or rims of brake discs or supermodel in the passengers seat) is a great thing!

It's a hobby - and the joy of working on the 8 doing whatever - was not on the options-list when the car was delivered from BMW.

It's what we do (me too!)

Here's what I wanted to say:
I simply disagree with broad statements like "a different part here will improve the car". I, personally, argue that "I do things to the car because it's my hobby and I want to do them". Neither one of those things can be a sensible thing - simply because the whole car is not sensible (which is why I like it).

So, when someone asks "does this or that improve the car?" - the answer has to be a straight "NO" (imho). However, if the same person were to ask "Do I get a sense of accomplishment and joy of doing this or that to the car?". Then, the answer can be YES!

That's all that I meant.

Lloyd:
I purchased the 3.91:1 M5 diff from "DickB" in Holland and as yet have not got around to fitting it. "TallTony" kindly gave me his impressions of the Pro's/Con's and I would be interested in your experiences. At the moment I get 22mpg as an all round fuel return, that includes "exciting" driving around the local roads and longer-distance motorway cruising. How serious is the 3.91:1 diff impact on consumption? I know this is subjective and is based on driving style etc etc but I wondered if we are talking about dropping to 12/15 mpg?

I have to say that this thread has been thoroughly enjoyable and interesting, in fact, one of the better ones I have followed. The debates are mature and informative and for whatever reasons you guys choose to tinker I think you should be commended. I often wish I was a bit less technically and mechanically challenged. Unless a degree of 'experimentation' goes on, none of us would ever learn anything, I for one have learned an awful lot from this forum and some of what you guys achieve is truly amazing. The most important thing that has been stated a couple of times is that nothing is irreversible. Keep up the good work and may the debates continue

I agree, I have learned alot from this thread also. Thanks

For those of us not lucky enough to own a CSi, fitting a LSD is a definite improvement over stock. The only reason BMW fit an open diff is cost. There's a reason why all M-cars, plus a few select older non-M BMWs (850 CSi, E36 328i Sport, E34 535i Sport, etc) are fitted with an LSD from the factory.

Some will say that ASC+T does the job of an LSD, but quite frankly it can only be considered to be doing a very poor job of it. I always switch ASC off when I drive my 840, as it's nothing more than a nuisance. I'm then faced with the classic "one wheel drive" that all powerful open-diff cars suffer on anything other than perfect surfaces. I'm aware of the "secret" mode of the ASC+T, but it's not really that helpful in my experience.

My E36 3-series daily driver is fitted with an LSD (aftermarket upgrade by myself to improve traction on the limit), and it's been a godsend in the snow. At my work just about every BMW was getting stuck in the car park, thanks to RWD and the one-wheel drive effect of an open diff. Mine didn't get stuck or need pushed once. My 840 hasn't turned a wheel since we've had snow, as I know it'll be hopeless with the wide tyres and open diff.

Don't think for a second that what BMW sends out the factory gate can't be improved upon. I'm an advocate for mostly-original cars, with no silly aftermarket wheels and other bling mods. But as stated by other posters, there are always compromises (especially when it comes to cost, even on a £64,000+ car) meaning there are definite improvements to be had.

Thanks for the great thread, extremely interesting and well-informed.

You have all convinced me to change my '97 840ci's diff to a 3.15 ratio as this will give 2500 RPM at a indicated 80MPH (real speed 76.5MPH) which sounds just perfect and almost identical to the 740i Sport!

Do your research on a swap into that year 840 Timm. IIRC it seems I remember a difference in flanges than what were on the earlier models, or the axles were different....something. Not that the proper case won't bolt in or anything, just a headsup.

Thanks, that's exactly the type of warning I need, I almost bought a '93 850i diff on a whim!

Zitat von Paul_M;72457

For those of us not lucky enough to own a CSi, fitting a LSD is a definite improvement over stock. The only reason BMW fit an open diff is cost.

AFIAK, the EURO-Spec CSi has an LSD (25% lock). It was the US-version (and maybe others?) that didn't. If I had the chance (and a CSi) I would def. go for the LSD.

Zitat von fuzzifikation;72467

AFIAK, the EURO-Spec CSi has an LSD (25% lock). It was the US-version (and maybe others?) that didn't. If I had the chance (and a CSi) I would def. go for the LSD.

All 850CSi have a limited slip differential (LSD) with 25% lock - even the USA version. The latter did not get the final drive cooler, though (amongst other goodies that were omitted). Paul just meant that an LSD is a good upgrade if you don't have a CSi.

an interesting thought - especially just before installation!. The common LSD swap (from the US based guys) to 3.15 uses the big case diff from the E32 7-series, especially the 750iL, this was normally available from the early 1990's onwards. The Evo from which your diff is sourced is also an early 1990's model (I assume). Do you think BMW would have "dumbed down" the diff for the E36, or just stuck it in as a bit of engineering overkill. I would think the latter, as there would be no additional cost.

Anyone think this logic is OK?

It's a large case diff, so probably much the same internals as the standard CSi diff. The M3 Evo was the only E36 to get this diff (even the 3.0 E36 M3 had the medium case diff). I doubt it'll have any problems handling the torque of the CSi.

Interesting aside - the 6-speed box used in the 840Ci (and 850CSi) has been shown to handle over 500 lb ft torque over a prolonged period. Bearing in mind that the 840 produces what 300 lb/ft? So it shows that, at least in this era, many components were very over-engineered.

Paul, if your post was meant to say that both getrag 6spd transmissions used in the E31 have the torque figures you stated ( I will assume you were talking about your 840 since that's what you have, and I'm not familiar with the CSI figures) then fine. However the way it's worded implies that both the 840 and CSI used the same transmission. They in fact do not, although I'm quite certain the smaller V8 S6S 420G tranny could handle the S70 power just fine.

Zitat von anguswolfendale;72452

Lloyd:
I purchased the 3.91:1 M5 diff from "DickB" in Holland and as yet have not got around to fitting it. "TallTony" kindly gave me his impressions of the Pro's/Con's and I would be interested in your experiences. At the moment I get 22mpg as an all round fuel return, that includes "exciting" driving around the local roads and longer-distance motorway cruising. How serious is the 3.91:1 diff impact on consumption? I know this is subjective and is based on driving style etc etc but I wondered if we are talking about dropping to 12/15 mpg?

Angus to be honest I dont ever worry about the mpg however it seems to return the same figuares for the journeys I do as before. I guess it should be less but I dont worry either way. No sure how helpful that is

Zitat von Paul_M;72508

Interesting aside - the 6-speed box used in the 840Ci (and 850CSi) has been shown to handle over 500 lb ft torque over a prolonged period. Bearing in mind that the 840 produces what 300 lb/ft? So it shows that, at least in this era, many components were very over-engineered.

Not only in that era.. also today ..

Here's why:
Manual transmissions (and only those) are specified to handle human error. That means that the transmission must not brake if some idiot changes to second gear when going 150mph (mind you that destroying the engine doing that has nothing to do with the tranny specs ).. Or he wants to take off spinning his wheels and just lets his foot slip off the clutch doing 5000 RPM in first gear (BANG :-))

So, really, a manual transmission is designed for the weight of the driveline and the mistreatment from 18 year old kids that want to show off their driving expertise to the girls at the cafe.

On the other hand:
An automatic tranny (or any electronically controlled transmission) does not have to handle such mistreatments as the electronic part does not allow them. So generally, they can handle much less torque albeit being used with the same engine/driveline.

Cheers,
D.

P.S.: the above is the reason why the big engine variants of the M70 (the 6 liter tuned things that produce 400+hp) require you to have the manual transmission (as those can actually handle the torque).