Diff upgraded

    Today I picked my car up after it has had rear diff upgraded.


    Here are my first impressions:-


    1) It certainly makes the car faster accelerating 0 - 60mph and makes the car seem much more positive and responsive.


    2) The approximate revs are now as follows in top gear :-


    80mph 2400rpm
    90mph 2800rpm
    100mph 3100rpm


    Tested on Motorway using Cruise Control in Drive Mode.


    For anyone who is interested here's what I did :-


    My car is an Euro 1997 840Ci Automatic Sport.


    It was originally fitted with standard 2.81:1 rear diff.


    I bought a 3.15:1 Limited slip diff from a 1990 BMW 750il from a UK BMW breaker for £300. This diff had 60k miles on it - but apparently these thing are bullet proof and mileage is not usually a consideration.


    In theory this should give me 12% more torque at the rear wheels.


    It was fitted by local mechanic in about 4 hours at cost of another £150.


    It was filled with standard BMW recommended LSD oil and they had to utilse the original diff casing.


    All in all I am delighted.


    For those more technically minded - the LSD is apparently preset at 25% locking - which will actually come into play before the standard 8 series traction control so if anything stabilise the rear end even further.

    Hi Nick,


    Don't worry - I'm not that technical either.


    Basically - our cars are produced to be Autobahn cruisers with the engines geared to cruise at 155 all day.


    Changing the rear diff is a very simple upgrade which "unlocks" some of the car horespower at lower speeds making it more responsive at lower speeds.


    If you imagine a racing bike with gear cogs front and back - I have changed the rear cogs- that's all.


    The trade off is that my car will probably top out at about 140mph - bummer :) - but will do 0-100 about 12% faster than previously.


    The Limited slip part also helps as it prevents the wheels spinning and distributes power evenly to the 2 rear wheels.


    The whole upgrade cost me £600ish.

    Re: Diff


    Zitat von nickcropper

    Thanks for the explanation..


    A top end of just 140mph - how you gonna cope with that? :wink:


    Have a great weekend!


    the low down power is worth it i would imagine! :lol:

    Differential upgrade


    Hi Guys. (that is Nick and Ian)


    You don't think I am going to let you have this "juicy" discussion without hopping in do you??? 8):P


    First congratulation on your upgrade Ian. You are going to love it. Your car now accelerate like a plane, and you feel your body pushing into the back seat.... wow. I was a bit surprised you upgraded to a 3.15. I thougt those with automatic trans upgrade to 3.64. You do have an automatic trans right? Also I wouldn't be surprised your top speed be 167MPH or so. If you check that out let me know.


    I mention this because this is what it is with mine. I upgraded from a 2.65 ratio to a 3.15. It shaves off some 35-40 Km/hre. That reduce the car speed from 303km -38km = 265Km or 165.6 MPH.


    I haven't checked that out personally yet but I will this spring since I will take the BMW course at a race track and plan to test that a little bit. Now I don't know if I have the gots to bring my car that fast yet. My personal top speed is a modest 200km/hre. Mind you I only have owned the car 6 weeks before storing it for winter. Not bad for doing it on a Max speed autoroute of 100Km/hre. I found that even the stuff that travels in the same direction than me comes fast.


    Now when you are ready for multiplying this acceleration effect "chip" the car. You will need a bigger tooth brush.


    That is it for now my friends from UK. Hope we meet one day.
    Would you guys plan to come for the International 8Fest in the US by any chances????

    Hi Le Transporteur,


    Yep, I'd be up for the 8Fest depending on work.


    I find the power of my 850 more than sufficient even though it is completely standard. My previous toy was a 1988 Ferrari Mondial which was a 3.2 V8 (same engine that's in the 328 GTS/B). There's much more torque with the 850 and I am quite sure if it was de-restricted, the top end would be higher also. Just the handling where the Ferrari wins - you know the expression "it felt like the car was on rails"..............completely unreliable tho, so it was expensive to maintain. But as I say to Sam, my wife, you can't put a price on enjoyment - right guys! :lol:


    I think if I upgrade my 850, I may firstly change the springs and drop the car slightly. If anyone has any recommendations/suggestions on this subject they would be more than welcome........I'm quite non-technical so be gentle with me - :oops:


    Nick


    PS Just got to say that it's so cool being part of such a friendly community!

    WOW Ferrari.....


    Yep, I'd be up for the 8Fest depending on work.
    I am thinking to invite a small bunch of people at my house in Canada for the 2005 8Fest just prior or after the celebrations.
    If such is the case would you like to be invited?


    I find the power of my 850 more than sufficient even though it is completely standard. My previous toy was a 1988 Ferrari Mondial which was a 3.2 V8 (same engine that's in the 328 GTS/B). There's much more torque with the 850
    I am pleasantly surprised the 8 can be compared to Ferrari. I am like you in a way. Not technically inclined, but also almost completely ignorant about cars. Until last October I had no inkling about cars. They were just to move me from point A to point B. In fact I didn't know what an 8 was, and had never come aboard a performance car. Nor ever went abord a BMW. Now I play catching up and read all I can. It doesn't sink in easy at 50+ years old, but I do my best. It is a new enjoyment. Now I don't mean that you are like me in any of those points, just the technically one :oops::P8):P


    and I am quite sure if it was de-restricted, the top end would be higher also.
    I am sure you are right. At least you are for here in Canada. My 8 was restricted to 250Km/hre. But having chip it removed that lock.


    But as I say to Sam, my wife, you can't put a price on enjoyment
    Tell your wife I said you are right. 8):twisted: You can bribe me later.... :D:wink:


    I think if I upgrade my 850, I may firstly change the springs and drop the car slightly.
    Mine has a racing suspension. K&N air, and Rhemus exhaust. Immoveable on the road. But I find it quite rough in town. I couldn't begin to explain how this is done though. The previous and 1st owner of the vehicle did a whole bunch of mods on it including 2 sets of Mags and crossed drilled ventilated brakes. I even had to ask him to explain what they were. :oops: Talk about ignorance. Bottom line for me is I am glad I got a car with all this already into it, because I couldn't have had them done myself.
    My strategy was.... I got my wife into letting me do a wallop of expenditure in one shot..... :):D:twisted: ...it worked.


    I'm quite non-technical so be gentle with me -
    my prefered sentence. :wink:


    If you do not frequent Roadfly, you may want to consider that. There is always mods, and repair talk going around. As great a community as this one.

    What a priviledge to be able to belong to them. (that is both community.


    Don't forget my idea about 8Fest.

    Hi,


    Yep, 8Fest sounds good and I'd love an invite to the pre Fest celebrtations!! :D Thanks!


    I'm slowly learing about the technical stuff. It's so refreshing to speak to people who are enthusiastic about sharing their knowledge!


    I'll spend some time on Roadfly this week. I tried to log on earlier but forgot my password ( :oops: ) and the e-mail I registered with is for my computer at work. I'll have to wait until tomorrow before I can get on.


    Have a nice evening!


    Nick

    Congratulations to you switch!


    Sounds impressive! I would love to time the car to see what you came up with. I would also love to be at the 8-fest, but this year I am organizing a big event myself and won´t find the time to do so! But anyways, enjoy your trips!


    Greetings from Hamburg,
    Marc
    aka Tranceshark

    Liebe Grüsse aus Braunschweig, Marc

    Zitat von nickcropper

    I think if I upgrade my 850, I may firstly change the springs and drop the car slightly. If anyone has any recommendations/suggestions on this subject they would be more than welcome........I'm quite non-technical so be gentle with me - :oops:


    Nick


    PS Just got to say that it's so cool being part of such a friendly community!


    Hi Nick,


    There is a lot of discussion on shock/springs upgrades on the roadfly board, if you search the archives there.


    In summary, most seem to endorse the H&R Sport Springs with the Bilstein Sport Shocks combination, in terms of aftermarket.


    If you want to stay with BMW equipment and don't have a CSI, upgrading to CSI shocks/springs should give you a more aggressive suspension, while staying factory.


    Please confirm this with other board members here or the archives at roadfly as I am going from my memory of what I've read, but I believe the CSI setup with lower your car an inch, and the H&R/Bilstein combo will lower it ANOTHER 1 to 1.5 inches.


    I've also read that it is important to confirm brand name compatability when mixing shocks and springs, as even when the two are physically compatable, within that compatability there are brands that perform together very differently. I.E. the Bilstein/H&R combo are reputed to work extremely well together.


    For what it's worth, I also remember reading an online poll on preferred upgrade path, weighing cost/benefit. Top three upgrades in that poll were:


    1. engine/transmission chip
    2. diff upgrade
    3. suspension upgrades (shocks/springs/sway bars/camber plates, etc.)


    Lots of folks also seem to like the 18" M-Parallel rims, though I'm partial to the throwing stars, myself.


    Hope this helps.


    - Rey

    I had the H&R's and Bilstein sports, worked great, I have pics of the car with the springs and 18" hand polished M-parallel wheels. Would post them if I knew how.
    AAARIMS sells 18x8 / 18x9.5" M-Parallel rims for $800. a set of 4. They are the machined face / lip. For $1200 us, they are available in chrome. Mine are the machined ones and came with 245/40/18 and 275/35/18 Kuhmo Estra Supre 712's for a grand total of $1400. mounted and ballanced with BMW emblems and chrome lug nuts included. These prices do not include shipping.

    Comments on thread...


    Thought I'd throw a few comments in--I've had a few phone calls from people reading this post who were confused about optimal differential ratios and suspension settings/issues.


    (1) The 840Ci with 5spd 2.81 does nicely with the 3.15LS upgrade mentioned above. A 3.64LS is also an option, but cruising rpm gets a bit high for comfortable highway cruising (3095rpm @80mph w/ the 5th gears .79 ratio). With tthe 3.15LS its mathematically 2678 rpm @80mph, so nice and smooth, and you get a nice gain in acceleration. 3.64 is a nice option if you don't travel on the highway much and would like to autocross, or track the car.
    (2) Upgrading to CSi suspension is an option but is expensive and will still leave the car with inadequate handling. Stock CSi suspension uses stiffer springs and shocks, however, fails to balance the car's "attitude" going through a turn. It's flaw is strong understeer or plowing when enterring or pushing the car hard through a turn. This is clearly seen in front tire wear when running the car hard through repeated turns on twisty roads or on the race track or autocross courses. The front tires wear very badly on the outside edge. The solution is to add a stiffer rear roll bar of approximately 19mm (K-Bars) and/or add about -2.0 degrees of camber to the front suspension settings using a camber "kit" such as K-Mac. Doing so balances the car and makes it capable of some pretty amazing performance (ever run through racing corners with a Supercharged Mini Cooper S?). Also removes the front tire wear issue from hard cornering.
    (3) Lowering heights are not additive--the CSi springs will lower the car about 1/2 inch OR the H&R Springs will lower the car approximately 1.25 inch. The H&R springs will not lower the car 1.75 inches, only 1.25 inches.


    Hope this helps clarify. Keep up the good work Phillipe.


    Greg K
    BMWe31.com

    94 840i or Ci tranny


    Hi!


    I am totally interested in the tranny swap but I'm a bit confused if my car is an 840i or Ci. Since mine is an early 94 I believe that the transmissions and engine are different, 4.0L opposed to 96+ 4.4L. Can any one confirm how I can identify my car? Would I still be able to do this mod regardless of my model?


    I would also like to chip my car. I have a K&N filter and MagnaFlow exhaust (mufflers only) What is the best set-up for this? How do the other chip manufacturer's compare by personal experience?


    As for suspension, I would like to lower the front a bit just to even out the gap. I have Bilstein shock with stock springs, would it be wise to just swap out the front springs with H&Rs?


    Has anybody drop in an M5 engine w/ 6-speed manual transmission in their 840? Is it possible, or not worth it? Is it better to just go with a Supercharger set-up like the one from Dinan?


    Lastly, does any one know where I can get these parts at a fair price or if they are still available:


    Dinan Supercharger
    Erubuni Front lip
    M5 style trunk lip (the small accent)


    I'm located in Southrn California. Any help is appreciated. I have also posted on other forums.


    Thanks,


    John

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