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Thread: Catalytic Converter replacement

  1. #51
    Join Date
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    M3, 850i, E30T, E55T
    Quote Originally Posted by mojocoggo View Post
    I've never noticed a change in sound going from OE to Magnaflow cats. I also only want a quiet OEM exhaust sound so I've always paid attention to any changes. I can't say I have any long-term experience with Magnaflow cats, and I wouldn't use them on my own car personally.

    My 850i had no cats when I bought it. I ended up just getting a used set of cats from a 60k mile car that was wrecked. I verified the smog history of the donor car (you can do so for free here: http://www.bar.ca.gov/pubwebquery/ve...pubtstqry.aspx) and it had passed every time it was tested, so I figured it would be a good bet.

    I would go with OEM on a car you plan to keep for at least 2-3 more smog tests.

    It all fit in my E24 pretty well.

    Attachment 576099
    How was the noise level with no cats?


    Sent from my SM-G935W8 using Tapatalk

  2. #52
    Join Date
    Mar 2007
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    Bay Area, CA
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    Not a Ferrari
    https://www.youtube.com/watch?v=l15sdDlUKaM

    This was with straight pipes and no cats.

    1995 540i/6 // Dylan Leff - www.originalplate.com


  3. #53
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    Color me confused.... Lol. Was it droney at all? I've got no mufflers and it sounds good now but my cats are smelling pretty bad so not sure if I should replace them or just delete them.

    Sent from my SM-G935W8 using Tapatalk

  4. #54
    Join Date
    Dec 2009
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    Gardendale, AL USA
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    1995 840 Ci, 1959 Sprite
    Just delete them. I really haven't noticed any louder sound at all. Still have the rear resonators at the exhaust tips. No droning that I can tell.

  5. #55
    Join Date
    Mar 2010
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    Vancouver, BC
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    1990 BMW 850i, 1976 Nova
    as soon as the law was changed to delete the local smog testing, bye bye cats... been 2 years now... feel confident in the free-flowing emissions...
    "...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge

  6. #56
    Join Date
    Apr 2008
    Location
    Los Angeles, CA
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    114
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    95 BMW 840Ci; 97 Toyota 4Runner Ltd
    Hi folks,
    Just wanted to give everyone an update...
    The OEM cats were definitely "disintegrated." A local shop cut/removed them and I decided to replace them with new Walkers, part number 80811. The part number was per Walker's website and AutoZone's website. The goal... passing my smog test, which I did this afternoon. Hoping for these Walker cats to be just fine in 2 years for the next test.
    Cheers.

    My 1995 BMW 840Ci
    Authentic OEM 18" M Parallels, Staggered Michelin Super Sports,
    Airbag Sports Steering Wheel 2,
    ACS-style aluminum pedals and more to come...

    wanted an 8 since college back in 1991; came to fruition in May 2007

    click for more pics->
    http://forums.bimmerforums.com/forum...05&postcount=1


  7. #57
    Join Date
    Jan 2017
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    The Netherlands
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    850i
    Old post, I know.
    My question is: the suggested Walker cats look very different form the stock cats. For example the stock cats have eccentric twin inlet pipes (pointing to the centre of the car), not straight. Hard to believe that installing Walkers is a straight forward exhaust job. Anyone has a picture of these Walkers installed under the car?
    Thanks, Albert

  8. #58
    Join Date
    Sep 2008
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    Santa Barbara
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    91 Dinan860 & 91 850 6sp
    The Walkers listed above (with pics) are the easiest to install.
    Any semi competent exhaust shop can do it and it looks just fine. No, this isn't something you want to do yourself with a hacksaw, pliers, clamps, & duct tape
    reading back through this thread, it might be good to point out that the twin pipes are INLETS and the single the outlet...
    The magnaflows can be adapted to work too, but they are much more work and, in my experience, do not last as long.
    Last edited by cartoonz; 11-18-2018 at 07:09 AM.
    '91 Dinan 860 Stage III (new 6L engine)
    '91 Dinan 850 TT stage III (brand new engine) 21st Century Tech meets 18th Century Dinan...
    '91 850i 6sp (mint) (sold)
    '90 Dinan 750iL TT stage III (Guido - The Beast)
    '94 850 CSi The Detroit Auto Show car (restored to factory perfect) (sold)
    '96 850Ci, The George Carlin car
    ''73 3.0 csi, '08 535i, '03 X5 4.6is
    ...and a few other non BMW cars

  9. #59
    Join Date
    Jan 2017
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    The Netherlands
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    850i
    Thanks cartoonz.
    I'll probably go for a set of BM90730 (L) and BM90731 (R) requiring no cutting or welding, just a simple replacement including pipes to exhaust manifolds. Price around 450 USD together, not bad I guess.
    Anybody used these replacement cats?

  10. #60
    Join Date
    Apr 2002
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    San Diego
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    1997 840ci
    Quote Originally Posted by cartoonz View Post
    The Walkers listed above (with pics) are the easiest to install.
    Any semi competent exhaust shop can do it and it looks just fine. No, this isn't something you want to do yourself with a hacksaw, pliers, clamps, & duct tape
    reading back through this thread, it might be good to point out that the twin pipes are INLETS and the single the outlet...
    The magnaflows can be adapted to work too, but they are much more work and, in my experience, do not last as long.
    Cartoonz, is your advice on the twin inlet Walkers limited to V12s or do you know if they will work on an 840ci M62 as well? Thanks.

  11. #61
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    Quote Originally Posted by DanB View Post
    Cartoonz, is your advice on the twin inlet Walkers limited to V12s or do you know if they will work on an 840ci M62 as well? Thanks.
    My experience is with the V12's, but there's no reason these wouldn't work with am M62...
    but, if memory serves me, the M62's have after-cat O2 sensors as well as the pre-cat pair... so be sure to weld in bungs for those. Simple job.
    Last edited by cartoonz; 11-29-2018 at 04:10 AM.

  12. #62
    Join Date
    Apr 2002
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    San Diego
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    1997 840ci
    Quote Originally Posted by cartoonz View Post
    My experience is with the V12's, but there's no reason these wouldn't work with am M62...
    but, if memory serves me, the M62's have after-cat O2 sensors as well as the pre-cat pair... so be sure to weld in bungs for those. Simple job.
    Much appreciated, will give those a shot.

  13. #63
    Join Date
    Jul 2013
    Location
    Oakland CA
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    My Cars
    10/91 850i, 1989 325is
    Reviving an ancient thread again. Great stuff mentioned.

    Times have definitely changed. I'm restoring my 850i and after getting all the engine bits done and its first start, it runs like a champ! However, I'm getting the burning plastic smell and smoke from the left bank exhausts only once they get hot.

    Car only has 70k on it, and it passed its last smog however, the guy I purchased it from drove it around 30 miles on 6 cylinders (epic facepalm). My theory is that the cats are soaked in fuel and as a result, started to melt. Excess fuel was also present on the plugs on that bank (CPS sorted it all out!)

    Point is, I'm certain I won't be able to do much about that cat. Not even sure how to clean it up without removing them. So I'm looking at getting some Walker 80832 cats incase they are screwed, but they don't exist anywhere! They're either completely out of stock or discontinued, but they're proving impossible to get hold of.

    Anyone got other suggestions here? I'm tempted to change just the one side if that's even possible, but based on all that's been said, I would like to avoid the Magnaflows too. Also i'm in CA, so got that whole mes

    Thanks all!

  14. #64
    Join Date
    Sep 2008
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    Santa Barbara
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    My Cars
    91 Dinan860 & 91 850 6sp
    Walker 81132 is the new version... and newer price @$311 each
    '91 Dinan 860 Stage III (new 6L engine)
    '91 Dinan 850 TT stage III (brand new engine) 21st Century Tech meets 18th Century Dinan...
    '91 850i 6sp (mint) (sold)
    '90 Dinan 750iL TT stage III (Guido - The Beast)
    '94 850 CSi The Detroit Auto Show car (restored to factory perfect) (sold)
    '96 850Ci, The George Carlin car
    ''73 3.0 csi, '08 535i, '03 X5 4.6is
    ...and a few other non BMW cars

  15. #65
    Join Date
    Jan 2008
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    Indianapolis, IN
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    93 850Ci, 09 Caddy SRX
    I frequently heard that some of the aftermarket converters failed within the CA 2yr test cycle. So, they had to be replaced and prorated for the remaining life expectancy. The smog test is already a PITA. I sourced a pair of “cats” from a fellow 8er who was parting a low mileage totaled vehicle. I found an exhaust shop willing to do the work (supposedly it’s illegal to install used cats???). The shop inspected the cats & said they appeared to indeed be from a low mileage vehicle. That was 6yrs ago & 3 successful test cycles…all passed with flying colors.

    I anticipate the next time I’ll need to worry about cats I’ll be too old to drive! That or in 25yrs….whichever comes first!
    1993 850Ci.....18 years & 165,000 miles and counting!

  16. #66
    Join Date
    Apr 2015
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    NJ
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    1995 BMW 850ci
    Please check out my work: (replacing a new cat was part of fixing the car, the thread is long, about 6 years, with lot of tears)

    https://www.bimmerforums.com/forum/s...4#post30679484

  17. #67
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    Jul 2013
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    Oakland CA
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    10/91 850i, 1989 325is
    Quote Originally Posted by cartoonz View Post
    Walker 81132 is the new version... and newer price @$311 each
    Bingo, thanks for shedding light on this.

    Going to take the cats off this weekend and inspect it properly. Not sure how serious the damage is but i'll order a cat anyway and get it put in there if my one is shot.

    Quote Originally Posted by TedBobo View Post
    I frequently heard that some of the aftermarket converters failed within the CA 2yr test cycle. So, they had to be replaced and prorated for the remaining life expectancy. The smog test is already a PITA. I sourced a pair of “cats” from a fellow 8er who was parting a low mileage totaled vehicle. I found an exhaust shop willing to do the work (supposedly it’s illegal to install used cats???). The shop inspected the cats & said they appeared to indeed be from a low mileage vehicle. That was 6yrs ago & 3 successful test cycles…all passed with flying colors.

    I anticipate the next time I’ll need to worry about cats I’ll be too old to drive! That or in 25yrs….whichever comes first!
    I've been looking but can't find any low mileage ones near me. I'll keep checking it out as i'd rather keep everything as OEM as possible, but i'm also not going to break the bank to achieve that. Already spent heaps on the restoration and i'd say i'm at the halfway mark haha! Still loads more to do!

  18. #68
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    Jun 2008
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    SF Bay Area
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    Quote Originally Posted by Moomar55 View Post
    Bingo, thanks for shedding light on this.

    Going to take the cats off this weekend and inspect it properly. Not sure how serious the damage is but i'll order a cat anyway and get it put in there if my one is shot.



    I've been looking but can't find any low mileage ones near me. I'll keep checking it out as i'd rather keep everything as OEM as possible, but i'm also not going to break the bank to achieve that. Already spent heaps on the restoration and i'd say i'm at the halfway mark haha! Still loads more to do!
    No licensed exhaust shop will install a used cat in California.
    I see you are in Oakland, PM me I think I can help.

  19. #69
    Join Date
    Apr 2015
    Location
    NJ
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    373
    My Cars
    1995 BMW 850ci
    NJ got rid of exhaust/smog test for cars older than 1996 - they were doing it with the sensor in the tail pipe. Actually, cars before 1996 are completely exempt from state inspections.

    The cat i installed was (on ebay) around $60 :

    2.25" Thunderbolt Universal Catalytic Converter - 410225 - NEW - Made In USA

    The 2.25" pipes work correctly.

    Now, only OBD2 ports are supported.

    The new cat gives excellent output, checked the O2 sensors and very stable. Its specs can definitely handle the car's 6 cylinders, and I don't see why it can't work forever.
    Of course, if its garbage, we will know when the check engine light comes up. But at this point, we are experts already lol.

    There doesn't appear to be a huge technical difference between OEM at $3000 and this generic cat at $60.

  20. #70
    Join Date
    Jan 2017
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    The Netherlands
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    850i
    Quote Originally Posted by wokke View Post
    I recently had a customer with an extremly nice '99 840Ci with broken (yes, phyically broken) ceramic internals in the cat converters.
    He didn't want any after market stuff welded in as he wants his car to look original. So I opened the original cats and emptied them entirely.
    Then I took two Magnaflow cats, cut them open, removed the monoliths and inserted them into the original cat housings.
    Has been a bit of work but now it looks original again and will pass smog tests even easier than before because of newer cat technology.
    I'm doing exactly that, using monolith's removed from universal JMJ 2-55 Polish cats (@ 65 Euro). Dimensions of a monolith are 8 x 12 cm and fit nicely in the original housing. Actually 3 would fit in each housing, but I guess cats have become so much more efficient in 3 decades. Original converters are 1800 Euro each from the dealer if at all available.

  21. #71
    Join Date
    Aug 2007
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    San Ramon, CA
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    1,421
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    850Ci, M5, Model-S P85D
    Anybody have any insight on the difference between the 750-M73 and 850-M73 BMW OE cat sections (down pipe flange to center-resonator slip joint)?
    I anticipate the cats are the same.

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