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Thread: Euro 3.91 diff install question

  1. #26
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    Quote Originally Posted by Budget M3 View Post
    How much? L/100km or mpg is fine. I can do the math ;-)
    My combined consuption increased about 1.5-2L/100km. I don't have that car anymore. I got so bored with it, that i sold it.

  2. #27
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    Quote Originally Posted by mikae31 View Post
    My combined consuption increased about 1.5-2L/100km. I don't have that car anymore. I got so bored with it, that i sold it.
    So about 1 mpg. That’s not too significant for a car that most of us drive sparingly. Probably decreases overall range by less than 20 miles on a long road trip which should be no big deal.

    - - - Updated - - -

    Quote Originally Posted by JDP530 View Post
    I joined forum several years ago when I first bought the E31 but haven't really been active on here until several months ago when I started working on my car. My son lives in Denver so I try to go up there a few times a year. We have both attended events at Pikes Peak Raceway and High Plains. I would like to drive my car up there this year but I am still working on it and having some issues to resolve.
    Thanks,
    John Patterson
    Hi John
    Hope you get the car sorted and that our paths cross soon!

  3. #28
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    Diff is in and my initial impressions are very positive. I'll have to wait and see about the mpg situation, but at least I can now drive the car in non-sport mode and not feel like a Geo Metro pulling away from stoplights

    I have sourced a second one--also 3.91 LSD. Actual mileage unknown but it feels tight and appears to be in very good shape...and comes with NEW properly sized bolts for swapping your output flanges! Not interested in shipping it though--these suckers are HEAVY!!! If anyone is interested in picking up in SoCal shoot me a PM. For an extra fee I could be persuaded to drop it off on the road between LA and Colorado this summer when I make that drive.
    Last edited by Budget M3; 03-23-2018 at 07:22 PM.
    "Asphalt is evil, it must be punished!"
    '89 Z1 Dream Black/Alcantara/Camo, Racing Dynamics, the coolest doors known to man -- Sunny days & Sundays
    '90 Z1 Red w/custom red/black French leather, Ground Control coil overs, BBS RV-F --Mais Oui!
    '91 850i Mauritius Blue/Black --1 of 179

    '85 M635CSi Alpine -- "Explosive!!!"
    '03 M3 Conv, Imola w/ SMG -- her daily driver
    '17 “30 Jahre” M3, Macao Blue -- 1/500 made


    Previously owned: 74 2002 (x2), 85 325e, 80 323i Baur, 94 325iC, 03 325CiC, 80 633CSi, 90 325iC, 98 318ti (Budget M3), 01 X5, 02 X5 4.6is (x2), 94 M3, 98 M3/4, 16 340i

  4. #29
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    Follow-up: According to the trip computer, I am getting ~12 mpg around town and ~18 mpg highway--both in economy mode. Realize that the trip computer is often a little optimistic, so these are not real world measurements. I am, however, pleased with the mpg performance of this upgrade. At 80mph in economy mode I am still turning less than 3000 rpm, so for me this is very comfortable (my exhaust is still louder than the engine at this engine speed ) In sport mode, the car now comes alive! As expected, mpg is affected more in sport mode--about 10.5mpg city versus 12mpg city in economy.

    The extra 3.91 LSD that I bought is now up and for sale in the classified ads. Shoot me a PM is you are interested...

    https://www.bimmerforums.com/forum/s...lent-condition
    Last edited by Budget M3; 04-08-2018 at 01:04 PM.
    "Asphalt is evil, it must be punished!"
    '89 Z1 Dream Black/Alcantara/Camo, Racing Dynamics, the coolest doors known to man -- Sunny days & Sundays
    '90 Z1 Red w/custom red/black French leather, Ground Control coil overs, BBS RV-F --Mais Oui!
    '91 850i Mauritius Blue/Black --1 of 179

    '85 M635CSi Alpine -- "Explosive!!!"
    '03 M3 Conv, Imola w/ SMG -- her daily driver
    '17 “30 Jahre” M3, Macao Blue -- 1/500 made


    Previously owned: 74 2002 (x2), 85 325e, 80 323i Baur, 94 325iC, 03 325CiC, 80 633CSi, 90 325iC, 98 318ti (Budget M3), 01 X5, 02 X5 4.6is (x2), 94 M3, 98 M3/4, 16 340i

  5. #30
    Join Date
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    Quote Originally Posted by Budget M3 View Post
    Follow-up: According to the trip computer, I am getting ~12 mpg around town and ~18 mpg highway--both in economy mode. Realize that the trip computer is often a little optimistic, so these are not real world measurements. I am, however, pleased with the mpg performance of this upgrade. At 80mph in economy mode I am still turning less than 3000 rpm, so for me this is very comfortable (my exhaust is still louder than the engine at this engine speed ) In sport mode, the car now comes alive! As expected, mpg is affected more in sport mode--about 10.5mpg city versus 12mpg city in economy.
    How was the install for you? Did you do it yourself or use a local shop?

    I have a 3.91 LSD sitting on garage floor, just waiting to accumulate rear bushings and other parts needed to overhaul the rear suspension before I install the diff. I also have the oversize antisway bar that will require a bit of welding to install mounts. I am getting about 14mpg around town and on local roads but I have a hard time staying out of the throttle!

  6. #31
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    Quote Originally Posted by mikae31 View Post
    ...Way overpraised mod.
    Car forums tend towards quick, retail, bolt-on solutions rather than strategic engineering.
    The specs being offered here today would make most people cringe.
    Ideally an equivalent effort and budget would be put into fixing the root cause rather than masking it.

  7. #32
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    Quote Originally Posted by Hyper View Post
    Car forums tend towards quick, retail, bolt-on solutions rather than strategic engineering.
    The specs being offered here today would make most people cringe.
    Ideally an equivalent effort and budget would be put into fixing the root cause rather than masking it.
    Ideally, you would just buy a faster/quicker car that was more economical to purchase, maintain and modify! But what's the fun in that! I agree on the strategy approach for most things, but not sure it's reasonably practical in the world of 8 series cars.
    Last edited by Chamberlin; 04-08-2018 at 04:56 PM.
    2006 R53 JCW (British Racing Green) - 1994 E31 840Ci 6spd (AVUS Blue)
    2021 F56 JCW (Rebel Green) - 2000 E38 740i Sport (Titanium Silver)
    2017 F26 X4 M40i (Carbon Black) - 2007 E91 328iT (Deep Green)
    2012 E82 135i M Sport (Marrakesh Brown) - 2015 E84 X1 (Cashmere Silver)
    2005 E53 X5 3.0i Sport (Kalahari Beige) - 2000 E36/7 M Roadster (Oxford Green)
    2000 E38 740i Sport (Oxford Green) - 1999 E36 M3 Coupe (Fern Green)
    1995 E31 840Ci Canadian (Oxford Green) - 2000 E36/8 M Coupe (Oxford Green)
    2004 E46 330Ci (Oxford Green) - 2001 E36/8 Z3 3.0i Coupe (Oxford Green)
    2002 E39 525i Sport (Oxford Green) - 2002 E36/7 M Roadster (Oxford Green)
    2001 E53 X5 3.0i Sport (Oxford Green) - 2007 E63 M6 (Silver Grey)
    1995 E31 840Ci (Oxford Green) - 2006 E86 M Coupe (Sepang Bronze)
    2001 E39 530i Sport (Aspen Silver) - 2009 E92 M3 (Space Grey)
    2001 E38 740i Sport (Sahara Beige) - 2008 E92 M3 (Melbourne Red)
    2000 E38 740i Sport Canadian (Sahara Beige) - 1997 E31 850Ci (Jet Black)

  8. #33
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    Quote Originally Posted by JDP530 View Post
    How was the install for you? Did you do it yourself or use a local shop?
    Install is fairly easy and straightforward. I took it to a local shop only because lying on my back underneath the car with a 100lb (exaggerated for effect ) diff balanced above my head was not desirable. The shop only charged me 3 hours labor which included all new seals on the rear cover and output flanges.
    Last edited by Budget M3; 04-08-2018 at 05:46 PM.
    "Asphalt is evil, it must be punished!"
    '89 Z1 Dream Black/Alcantara/Camo, Racing Dynamics, the coolest doors known to man -- Sunny days & Sundays
    '90 Z1 Red w/custom red/black French leather, Ground Control coil overs, BBS RV-F --Mais Oui!
    '91 850i Mauritius Blue/Black --1 of 179

    '85 M635CSi Alpine -- "Explosive!!!"
    '03 M3 Conv, Imola w/ SMG -- her daily driver
    '17 “30 Jahre” M3, Macao Blue -- 1/500 made


    Previously owned: 74 2002 (x2), 85 325e, 80 323i Baur, 94 325iC, 03 325CiC, 80 633CSi, 90 325iC, 98 318ti (Budget M3), 01 X5, 02 X5 4.6is (x2), 94 M3, 98 M3/4, 16 340i

  9. #34
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    Quote Originally Posted by Hyper View Post
    Car forums tend towards quick, retail, bolt-on solutions rather than strategic engineering.
    The specs being offered here today would make most people cringe.
    Ideally an equivalent effort and budget would be put into fixing the root cause rather than masking it.
    People get so hung up on mpg as a big cost issue. A difference of 2mpg city on a car that is driven 10k city miles per year costs about $500 at $3 per US gallon--big whoop. The cost is less when highway miles are factored in or when gas is cheaper. It is much, much less on a car that is driven less than 10k which most of our 8-series are (I only put about 3-4k per year on mine).

    So where would you put your $1500, Hyper?
    Last edited by Budget M3; 04-08-2018 at 07:58 PM.
    "Asphalt is evil, it must be punished!"
    '89 Z1 Dream Black/Alcantara/Camo, Racing Dynamics, the coolest doors known to man -- Sunny days & Sundays
    '90 Z1 Red w/custom red/black French leather, Ground Control coil overs, BBS RV-F --Mais Oui!
    '91 850i Mauritius Blue/Black --1 of 179

    '85 M635CSi Alpine -- "Explosive!!!"
    '03 M3 Conv, Imola w/ SMG -- her daily driver
    '17 “30 Jahre” M3, Macao Blue -- 1/500 made


    Previously owned: 74 2002 (x2), 85 325e, 80 323i Baur, 94 325iC, 03 325CiC, 80 633CSi, 90 325iC, 98 318ti (Budget M3), 01 X5, 02 X5 4.6is (x2), 94 M3, 98 M3/4, 16 340i

  10. #35
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    Too many ;-)
    Quote Originally Posted by Chamberlin View Post
    Ideally, you would just buy a faster/quicker car that was more economical to purchase, maintain and modify! But what's the fun in that! I agree on the strategy approach for most things, but not sure it's reasonably practical in the world of 8 series cars.
    ^^ +1 The 8-series has never been and will never be a fast car. It has always been and will always be an experience. Even in car crazy and jaded SoCal where on any given weekend you can find a C&C with rare Ferraris, Lambos, Corvettes, Porsches, Jags and other assorted unobtainium, the 850i still draws crowds for its rarity and design.
    "Asphalt is evil, it must be punished!"
    '89 Z1 Dream Black/Alcantara/Camo, Racing Dynamics, the coolest doors known to man -- Sunny days & Sundays
    '90 Z1 Red w/custom red/black French leather, Ground Control coil overs, BBS RV-F --Mais Oui!
    '91 850i Mauritius Blue/Black --1 of 179

    '85 M635CSi Alpine -- "Explosive!!!"
    '03 M3 Conv, Imola w/ SMG -- her daily driver
    '17 “30 Jahre” M3, Macao Blue -- 1/500 made


    Previously owned: 74 2002 (x2), 85 325e, 80 323i Baur, 94 325iC, 03 325CiC, 80 633CSi, 90 325iC, 98 318ti (Budget M3), 01 X5, 02 X5 4.6is (x2), 94 M3, 98 M3/4, 16 340i

  11. #36
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    997tt,850,02m5,w140 s500
    Quote Originally Posted by Budget M3 View Post
    Diff is in and my initial impressions are very positive. I'll have to wait and see about the mpg situation, but at least I can now drive the car in non-sport mode and not feel like a Geo Metro pulling away from stoplights

    I have sourced a second one--also 3.91 LSD. Actual mileage unknown but it feels tight and appears to be in very good shape...and comes with NEW properly sized bolts for swapping your output flanges! Not interested in shipping it though--these suckers are HEAVY!!! If anyone is interested in picking up in SoCal shoot me a PM. For an extra fee I could be persuaded to drop it off on the road between LA and Colorado this summer when I make that drive.

    wait, i thought all i had to do was change the output flanges and rear cover... whats this about the bolts now?

  12. #37
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    Quote Originally Posted by btnh View Post
    wait, i thought all i had to do was change the output flanges and rear cover... whats this about the bolts now?
    Don't have to, just a good idea.... to get away from the hex heads and over to the later spec E-TORX bolts.
    2006 R53 JCW (British Racing Green) - 1994 E31 840Ci 6spd (AVUS Blue)
    2021 F56 JCW (Rebel Green) - 2000 E38 740i Sport (Titanium Silver)
    2017 F26 X4 M40i (Carbon Black) - 2007 E91 328iT (Deep Green)
    2012 E82 135i M Sport (Marrakesh Brown) - 2015 E84 X1 (Cashmere Silver)
    2005 E53 X5 3.0i Sport (Kalahari Beige) - 2000 E36/7 M Roadster (Oxford Green)
    2000 E38 740i Sport (Oxford Green) - 1999 E36 M3 Coupe (Fern Green)
    1995 E31 840Ci Canadian (Oxford Green) - 2000 E36/8 M Coupe (Oxford Green)
    2004 E46 330Ci (Oxford Green) - 2001 E36/8 Z3 3.0i Coupe (Oxford Green)
    2002 E39 525i Sport (Oxford Green) - 2002 E36/7 M Roadster (Oxford Green)
    2001 E53 X5 3.0i Sport (Oxford Green) - 2007 E63 M6 (Silver Grey)
    1995 E31 840Ci (Oxford Green) - 2006 E86 M Coupe (Sepang Bronze)
    2001 E39 530i Sport (Aspen Silver) - 2009 E92 M3 (Space Grey)
    2001 E38 740i Sport (Sahara Beige) - 2008 E92 M3 (Melbourne Red)
    2000 E38 740i Sport Canadian (Sahara Beige) - 1997 E31 850Ci (Jet Black)

  13. #38
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    Quote Originally Posted by Budget M3 View Post
    Even in car crazy and jaded SoCal where on any given weekend you can find a C&C with rare Ferraris, Lambos, Corvettes, Porsches, Jags and other assorted unobtainium, the 850i still draws crowds for its rarity and design.
    Ain't that the truth...just try attending the local Cars & Coffee!
    1993 850Ci.....18 years & 165,000 miles and counting!

  14. #39
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    Quote Originally Posted by Chamberlin View Post
    Don't have to, just a good idea.... to get away from the hex heads and over to the later spec E-TORX bolts.
    Correct that you don’t have to change the bolts but it’s never a bad idea to replace 25+ year old high stress metals with newer, stronger parts. In my case the bolts were a grade of steel above the original and cost less than $1 per bolt.
    "Asphalt is evil, it must be punished!"
    '89 Z1 Dream Black/Alcantara/Camo, Racing Dynamics, the coolest doors known to man -- Sunny days & Sundays
    '90 Z1 Red w/custom red/black French leather, Ground Control coil overs, BBS RV-F --Mais Oui!
    '91 850i Mauritius Blue/Black --1 of 179

    '85 M635CSi Alpine -- "Explosive!!!"
    '03 M3 Conv, Imola w/ SMG -- her daily driver
    '17 “30 Jahre” M3, Macao Blue -- 1/500 made


    Previously owned: 74 2002 (x2), 85 325e, 80 323i Baur, 94 325iC, 03 325CiC, 80 633CSi, 90 325iC, 98 318ti (Budget M3), 01 X5, 02 X5 4.6is (x2), 94 M3, 98 M3/4, 16 340i

  15. #40
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    Quote Originally Posted by Budget M3 View Post
    ...So where would you put your $1500, Hyper?
    I'm a big fan of high compression and its efficiency.
    For instance, I've completed both a diff mod AND also tried out a compression boost.
    Seems they both delivered the same feel-good factor.
    My B46 project notes had me at 25 mpg highway, with both the diff mod and high CR swap combined.
    If I were saddled with an M70 and a $1500 budget I would park the dollars in pistons, to lift the entire torque curve.
    We are then forced into premium gas but we do recover our Grand Tour range.
    ******
    My latest trip to SoCal had me disappointed, because SoCal has definitely changed and the "car crazy" theme no longer applies.
    Twenty->thirty years ago, unique rides got acknowledged.
    Not so now. Instead its a mass SUV culture, mile after mile.
    Shocking compared to what it use to be.

  16. #41
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    Quote Originally Posted by Hyper View Post
    I'm a big fan of high compression and its efficiency.
    For instance, I've completed both a diff mod AND also tried out a compression boost.
    Seems they both delivered the same feel-good factor.
    My B46 project notes had me at 25 mpg highway, with both the diff mod and high CR swap combined.
    If I were saddled with an M70 and a $1500 budget I would park the dollars in pistons, to lift the entire torque curve.
    We are then forced into premium gas but we do recover our Grand Tour range.
    ******
    My latest trip to SoCal had me disappointed, because SoCal has definitely changed and the "car crazy" theme no longer applies.
    Twenty->thirty years ago, unique rides got acknowledged.
    Not so now. Instead its a mass SUV culture, mile after mile.
    Shocking compared to what it use to be.
    So I have to tear open my engine to do a piston swap in order to achieve better results? Assuming my labor is free, maybe that’s a good solution but my time is certainly not free. Doubt that I could pay someone to do the job including parts and labor for less than double that price.

    Not sure where you call home, but get off the freeway next time you come to SoCal. The car culture is alive and well on any given Saturday or Sunday C&C. You’re missing out.

  17. #42
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    Quote Originally Posted by Budget M3 View Post
    So I have to tear open my engine...
    And the problem is???

    *****
    I'm currently NoCal silicon valley, but I spent 4+1 years pulling an engineering degree out of UCLA which is/was (google-google) across the road from my family home in BelAir.
    Yep, I've known SoCal for 5 decades, and my eyes work just fine. And so does my memory.

  18. #43
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    Quote Originally Posted by Hyper View Post
    And the problem is???

    *****
    I'm currently NoCal silicon valley, but I spent 4+1 years pulling an engineering degree out of UCLA which is/was (google-google) across the road from my family home in BelAir.
    Yep, I've known SoCal for 5 decades, and my eyes work just fine. And so does my memory.
    The problem is time (or lack thereof). Everyone has skills, but not all of us have the same level of expertise or experience. What may take one person 3-4 hours because they’ve done it before (or have training that assists them in learning more quickly), may take another person 3-4 days to do the same job as they learn it OJT—it’s called a learning curve.

    I’m sure your memories growing up in SoCal were different and the culture has changed. That doesn’t make it any less of a car culture, albeit perhaps different than what you’ve previously experienced. It’s not better or worse, it’s just different. ...and I still get thumbs’ up for everything from my 850i to my Z1. Even my 318ti used to get compliments from those that knew what it was.

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