Pondering E36 M3 Evo diff

Zitat von TallTony;72373

Both myself and Wayne (Blackwell) have, and in Wayne's case had, the 3.91 diff. Neither of us thought that 1st was too short, even at the extreme end of the ratio change. Pottering around town in lightfooted D mode is not much different to before since the gears simply change with the revs applied. However IF you want you can make the car more twitchy (another scientific term), and more importantly from a standing start the car flies away from standstill as the power band is reached much more quickly and sustained for longer during hard acceleration.

Whilst there are theories to dismiss the modification, I am talking solely from personal experience (as I have it actually fitted). If my life changed to involve a lot of cross country travelling, at high cruising speeds, then I would be the first to change back, BUT since 90% of my driving is on twisties or around town then I am more than happy to keep my faster version of the car. Not sure that a small change in ratio would be noticeable or even desireable due to the costs involved doing it, but looking at this thread and all the other ones regarding ratio changing, there is plenty of info for you to decide which side of the fence you would prefer to sit on

Since I now use a paddle shifter in S mode, the ratio change is even better. The revs are higher, and the power is on tap more. Seriously, my car even with a standard engine is no slouch now, and only supercars have a chance of embarrasing me

TT

you claim your car runs to 60 1.5 secs faster than stock, so say 0-60 in 6 secs for Instance, yet after spending £8k on a Supercharger mine would only reach 60 in 5.3 sec? I'd say you've got a good deal there.

As for the Super car bit& to prove a point,would you like to run yours along side my 'Non Supercar Alpina' Hhmmmmm

Top speeds in each gear for the 850CSi running stock tires (265/40ZR17). The given speeds are at the rev limiter so you'll usually shift a lot sooner to the next gear. That's also beyond the engine's power peak, so the car may not be able to reach those theoretic top speeds due to wind and rolling resistance. The 2.93:1 final drive ratio is stock for the 850CSi.

1st gear (6400 rpm, 4.254:1)
• 2.93:1 final drive: 62 km/h (39 mph)
• 3.15:1 final drive: 58 km/h (36 mph)
• 3.23:1 final drive: 57 km/h (35 mph)
• 3.45:1 final drive: 53 km/h (33 mph)
• 3.64:1 final drive: 50 km/h (31 mph)
• 3.91:1 final drive: 47 km/h (29 mph)

2nd gear (6400 rpm, 2.534:1)
• 2.93:1 final drive: 105 km/h (65 mph)
• 3.15:1 final drive: 97 km/h (61 mph)
• 3.23:1 final drive: 95 km/h (59 mph)
• 3.45:1 final drive: 89 km/h (56 mph)
• 3.64:1 final drive: 84 km/h (53 mph)
• 3.91:1 final drive: 78 km/h (49 mph)

3rd gear (6200 rpm, 1.682:1)
• 2.93:1 final drive: 153 km/h (95 mph)
• 3.15:1 final drive: 142 km/h (89 mph)
• 3.23:1 final drive: 138 km/h (87 mph)
• 3.45:1 final drive: 130 km/h (81 mph)
• 3.64:1 final drive: 123 km/h (77 mph)
• 3.91:1 final drive: 114 km/h (72 mph)

4th gear (6200 rpm, 1.235:1)
• 2.93:1 final drive: 208 km/h (130 mph)
• 3.15:1 final drive: 193 km/h (121 mph)
• 3.23:1 final drive: 189 km/h (118 mph)
• 3.45:1 final drive: 177 km/h (110 mph)
• 3.64:1 final drive: 167 km/h (105 mph)
• 3.91:1 final drive: 156 km/h (97 mph)

5th gear (6000 rpm, 1.000:1)
• 2.93:1 final drive: 249 km/h (155 mph)
• 3.15:1 final drive: 231 km/h (144 mph)
• 3.23:1 final drive: 225 km/h (141 mph)
• 3.45:1 final drive: 211 km/h (132 mph)
• 3.64:1 final drive: 200 km/h (125 mph)
• 3.91:1 final drive: 186 km/h (116 mph)

6th gear (6000 rpm, 0.831:1)
• 2.93:1 final drive: 299 km/h (187 mph)
• 3.15:1 final drive: 278 km/h (174 mph)
• 3.23:1 final drive: 271 km/h (170 mph)
• 3.45:1 final drive: 254 km/h (159 mph)
• 3.64:1 final drive: 241 km/h (150 mph)
• 3.91:1 final drive: 224 km/h (140 mph)

The 3.23:1 mattsimis proposes will not make much of a difference in daily driving but I don't think the "performance gains" will be very noticable. It should be quite obvious that a 3.91:1 kills the car. You need an extra shift for about everything. Whatever you gain in acceleration you lose in shifting. Is the 3.91:1 a bad final drive? Of course not, but it's not really an option for the gear ratios of the manual 6 speed gearbox.

Just to add my twopennorth: I exchanged my stock (2.93:1 ?) diff on my M73 850 for a 3.15:1 fitted to a Quaife ATB - IMHO and I know that's not a particularly scientific appraisal, the car is noticeably faster off the line than before. I find that the 3.15 really suits the power coming from my engine - it's an M73 with a few re-programming mods (Firebird in the USA) and puts out a conservatively estimated 350hp at the flywheel. I haven't dyno tested the car nor have I made a comparison to a stock M73, as I said, it's only my opinion but my car does seem faster.

BTW, if anyone is looking for an LSD unit for an 8 I have one sitting in the shed in Norfolk, I also have my stock CWP set that could be fitted to it or any other suitable CWP could be fitted. Offers from any direction?

As far as I know there's absolutely nothing wrong with the LSD, I didn't use it because I decided to go for the Quaife unit instead.


PS, I shied away from going for anything "taller" than 3.15 as I do a considerable amount of cross-continent style long distance and wanted quicker bottom end without sacrificing too much top end speed - those German autobahns are really rather good you know

Zitat von mattsimis;72379

Argonaut, sounds good, how is your cruise RPM (70-90mph) RPM affected?

Hi, hardly affected, cruising RPM is up maybe around 400 to 500 rpm only, crusing at 80mph is around 2500

Ironically I need that diff now Jason, It's nearly perfect for my 6spd swap to change from the 2.65, but I'd love to find a 3.23. Believe me folks I can vouch that it's an extremely clean and flawless unit.

Zitat von rcrad6653;72387

Ironically I need that diff now Jason, It's nearly perfect for my 6spd swap to change from the 2.65, but I'd love to find a 3.23. Believe me folks I can vouch that it's an extremely clean and flawless unit.

Oh my, and how much was the P&P last time Randy? Talk to me off-line, if you need it we can sort something out.
Cheers

Alan, Gents
I'm following this thread with some interest, as I'm considering a somewhat similar swap - but want to keep my original casing (and cooling). Most likely I will go to 3.45 -- and maybe Quaife internals.
If you followed "martinw"s postings here, he points out you'll need to change the both the input flange, and both output flanges (as they are larger on the CSi) if you swap casings.

http://www.8er.org/forum/showthread.php?t=7647

Good luck, and post pics when you're done
Cheers Keith

Ok All

You have wet my appetite. What is the cost of swapping a diff? What would I need to do to my 4.4ci to shave about a second off its 0-60?

What about weight reduction? stainless exhausts and decat? lightened flywheels, removing various bits?

This might be a dumbass question but why would BMW spend millions developing a car and then put the wrong diff in it?

Radron: If you are seriously interested in making your car (a lot) faster, consider a supercharger kit. There is a huge selection of these for your M62 engine, giving you from 400 hp to almost 600 hp.. that should do it. And on the plus side: You could keep your diff!

As far as weight reduction goes: Not a chance. Unless you throw out the seats, doors, trunk and so on you can - at most - shave of a few kgs which will not make a noticable difference. Actually, I consider removing weight "blindly" quite a big danger to the car balance.

Nifty: BMW has put in the right diff - of course! The truth of the matter is, that many people love their car so much that they want to "make it their own" by "improving it". Usually, this results in a worse car. But this doesn't matter as one's perception will deceive oneself in making one believe that it is now better because of one's changes.

It's all just playing around

When I do the manual transmission swap this spring I am quite confident this will result in a completely different feel with the car. Literally of course it's different, but the fact the engine isn't spinning up that big 'ol torque converter will change things and a different well matched 'shorter' differential ratio (higher numerically) from the stock 2.65 will transfer power faster and to me, better. As Fuzz said 'better' is subjective to the individual and this is not to say it's better than BMW originally built, but it was designed as a fast GT cruiser and I want it a little quicker because that's the type of driving this car will primarily see. Weight reduction is a good thing but it's been shown many times that anything even marginally significant results is insulting the true character of the car, and it's certainly not better. I'll confine my weight reductions to things like lighter calipers and wheels.... areas of unsprung weight and rotating mass that will be an improvement and things I can see and feel.

Zitat von Nifty50;72428

This might be a dumbass question but why would BMW spend millions developing a car and then put the wrong diff in it?

Definitely not a daft question, what has to be remembered though is that as in all cases of motor and car production, compromises are met along the way between drawing board and finished product. I am sure that BMW fitted the best diff for the purpose for which the car was originally conceived (by BMW), the "problem" if you can call it that is that many other peoples expectations are different so whilst one will think the BMW OEM set-up is perfect, the next can see room for improvement. At the end of the day we shouldn't lose sight of the fact that our hobby revolves around a hunk of metal, no matter what we do to it it will remain a hunk of metal, albeit a nice shiny one with an interesting shape. Some will love it and others will show the true opposite of love, not hated but total indifference. Some people are just not interested in cars.

Anyway, back OT, I swapped my diff not because it was the wrong one but because I wanted slightly more lower end grunt, I'm pleased with the result and wouldn't necessarily agree that I made the car worse by doing this. In any event, none of the alterations I make to my car are irreversible and if desired, it could be returned to as-it-left the factory condition.

I agree with the reduction of unsprung weight. I would focus on rotating parts, especially (not sooo much the calipers, but them, too, of course). That is: drilled standard size discs and 17" CSi rims (at the most 18" rims - anything bigger will be noticably slower )

Also, what many people forget: They install giganormeous brake systems which introduce a LOT of weight. Actually, it's like installing the moon to your front wheels.
Then they are forced to buy huge rims (which, again, weigh a ton) and the gross result is significantly slower 0-60 time and noticably worse handling..

Don't we just love making our car worse just to pretend it's better, afterwards

Oh, and back to topic on the diff: Yes, the speed range is fully up to personal taste and it will not make the car worse to drive (as far as handling is concerned). However, the additional fuel consumption would bother me, personally. Not that I couldn't deal with the expense.. I just deem it unnecessary. But: It's all personal taste.

Lol.....I like the term giganormeous....:) I only need to locate the E31 Throwing Stars and I'm there Fuzz. In my case I have the aftermarket big Brembo calipers and 332mm drilled front rotors, Wilwood 4 piston rear calipers and 328mm vented/drilled. While true the rotors are heavier than what I had originally, the calipers are lighter than OEM CSI. I can even go to the front 2pc. 345mm CSI front rotors. All this will be in spec with what BMW originally offered but better, the balance isn't affected and should give a noticable improvement on my US-spec brakes. After all, if I'm getting there quicker with the diff change I might as well stop her a little better too in the bargain, at least as good as the euro CSI....:) Of note is that I would never have gone out and purchased these components new, just that a deal I couldn't pass by crossed my path.

Rad,

I, personally, think that the standard M70 brakes are somewhat too weak. I also argue that they wouldn't pass a modern car's brake specs. So the big brake kit is not such a bad thing..

And here's a question for you: Do 17" rims (let's say the throwing stars) fit on the big brake kit?

(I probably wouldn't spend the money on the kit unless a bargain crossed my way, too.. but it would be good to know as I do not in the world want to mount 18" rims.. I would miss the comfort.. and again: it's personal preference )

Well fuzz, I'll have to get back to you on that. I currently have 17" MK Motorsport MK1 wheels on the car (8.5-ET13/10-ET20-74.1 bore) I went with these because I too like the extra sidewall cushion and the design. I will know within the next two weeks whether they'll fit over those big front Brembos and 332mm rotors. We're in a deep freeze like Britain right now so I'm waiting for a warm window of opportunity. My logic was that the CSI used 345mm rotors with their caliper design behind the 17" Throwing Stars, but the Brembos are bigger than those. I have 10mm hubcentric spacers for the 17s that will help in that regard if they won't fit without. If all else fails I have another set of E31-specific MK1 18" wheels. I guess it will be a fair tradeoff if I have to use the 18s, and I would never go larger unless, as may be the case, I had to.

Thanks for the response.

I think my preference would be to keep the 8 as it is as it is a wonderful car. I might see how the wife feels about me borrowing some school fees for a track toy as well!

Well its nice to pretend isn't it?

Sorry for the random interuption to a very interesting thread!

We get this polarisation everytime someone does a modification to the apparently hallowed 8er. It is just an old car guys

Looking through this thread again there is developing theme of dont mod your car because God (BMW) presented you with a perfect design to begin with.....

It's pretty obvious which side of the fence I sit when it comes to changing things from stock. I'm perfectly happy to sit here and defend the extreme 3.91 diff I have fitted, on several grounds, especially as I still have the old one which could be refitted at any stage in the last 3 years, but hasnt been. There is a reason for this. I like it. It improved the car for me because it makes it behave in a way I like. I certainly do not 'pretend' that my car is better just because I have changed something. That is a bit of broadside that I cannot ignore or let go without comment. But I'll leave it there.

I have a lot of respect for those who fastidiously maintain their car in showroom condition. It takes a lot of effort to do so. I just cant live my life like that. Have you ever decorated your house ? Or bought a better telly even though the one you owned was cutting edge at the time of purchase ? I guess not. That's my real point here despite me rambling on somewhat again. It's not that I know better than BMW, it's just I know what I like and BMW didnt provide me with everything at point of sale (to the original owner :))

I'm of to do some work. Cheers