WTB: M5 catalytic converter

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Fanclutchnut
Posts: 14
Joined: Jan 05, 2021 8:32 PM
Location: Westchester Co NY

WTB: M5 catalytic converter

Post by Fanclutchnut »

Hi,

Our recently acquired M5 needs a cat section. I know the DEC version is available new but thought I’d check in here as well.
Open to oem and aftermarket functioning preferably.

Thanks,
bigwave
Posts: 170
Joined: Apr 03, 2013 10:43 PM
Location: Buffalo

Re: WTB: M5 catalytic converter

Post by bigwave »

Not sure what the "DEC" version is, though this one is extremely well made. I installed one on my car a couple years back since the OEM one was NLA and I couldn't be more pleased. Was a direct bolt up and it fit perfectly. http://www.vsr1.com/e28e24-m5m6-page/
Fanclutchnut
Posts: 14
Joined: Jan 05, 2021 8:32 PM
Location: Westchester Co NY

Re: WTB: M5 catalytic converter

Post by Fanclutchnut »

Hi Bigwave thanks for the reply and suggestion of the VSR1 part. The rest of the exhaust is not stainless so I didn’t think pairing that with it would make sense but it’s a good option to know about.

The DEC is the one that’s available though rockauto.
bigwave wrote: Apr 05, 2021 10:25 PM Not sure what the "DEC" version is, though this one is extremely well made. I installed one on my car a couple years back since the OEM one was NLA and I couldn't be more pleased. Was a direct bolt up and it fit perfectly. http://www.vsr1.com/e28e24-m5m6-page/
jhh925
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Joined: Jul 11, 2015 12:23 AM
Location: San Francisco Bay Area

Re: WTB: M5 catalytic converter

Post by jhh925 »

Fanclutchnut: I notice that you're not in CA, so short term, you may not care, but the VSR1 unit will not pass the CA visual inspection, and most "hi-flow" cats won't be enough to scrub the exhaust even if the smog station doesn't poke around under the car.
Fanclutchnut
Posts: 14
Joined: Jan 05, 2021 8:32 PM
Location: Westchester Co NY

Re: WTB: M5 catalytic converter

Post by Fanclutchnut »

Thanks for the heads up! Yes, we’re in NY. Im trying to get familiar with the NYS rules. It looks like the DEC unit isn’t high flow and is NYS compliant because of the age of the car.

PS LOVING your build. Very inspirational. We’ve referred to some of your great photos a few times already.
jhh925 wrote: Apr 07, 2021 5:15 PM Fanclutchnut: I notice that you're not in CA, so short term, you may not care, but the VSR1 unit will not pass the CA visual inspection, and most "hi-flow" cats won't be enough to scrub the exhaust even if the smog station doesn't poke around under the car.
jhh925
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Joined: Jul 11, 2015 12:23 AM
Location: San Francisco Bay Area

Re: WTB: M5 catalytic converter

Post by jhh925 »

Fanclutchnut wrote: Apr 07, 2021 5:22 PM Thanks for the heads up! Yes, we’re in NY. Im trying to get familiar with the NYS rules. It looks like the DEC unit isn’t high flow and is NYS compliant because of the age of the car.

PS LOVING your build. Very inspirational. We’ve referred to some of your great photos a few times already.
jhh925 wrote: Apr 07, 2021 5:15 PM Fanclutchnut: I notice that you're not in CA, so short term, you may not care, but the VSR1 unit will not pass the CA visual inspection, and most "hi-flow" cats won't be enough to scrub the exhaust even if the smog station doesn't poke around under the car.
Thanks!
wkohler
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Re: WTB: M5 catalytic converter

Post by wkohler »

DEC unit works fine and fits fine, but there were some discussions a few years back about making sure you get the proper E28 fitment cat vs the E34 one, which does still work, but is slightly different. Last year I worked on (and sold on BaT) an M5 with a DEC cat. While I had it off to do guibo, trans mounts, etc, I found that the cats used in the assembly are in fact CARB-approved, but those numbers are on the top, so I photographed them while the cat was out just in case it was an issue for smog for the then-current owner and also provided the photo to the new owner who is also in CA.
Fanclutchnut
Posts: 14
Joined: Jan 05, 2021 8:32 PM
Location: Westchester Co NY

Re: WTB: M5 catalytic converter

Post by Fanclutchnut »

That’s great to hear Chris! I did read that thread where DEC sent 3 e34 cats before correctly sending the e28 part. Hopefully I’ll have a differing experience! Looks like I’m placing my order today.

wkohler wrote: Apr 09, 2021 11:46 PM DEC unit works fine and fits fine, but there were some discussions a few years back about making sure you get the proper E28 fitment cat vs the E34 one, which does still work, but is slightly different. Last year I worked on (and sold on BaT) an M5 with a DEC cat. While I had it off to do guibo, trans mounts, etc, I found that the cats used in the assembly are in fact CARB-approved, but those numbers are on the top, so I photographed them while the cat was out just in case it was an issue for smog for the then-current owner and also provided the photo to the new owner who is also in CA.
jhh925
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Joined: Jul 11, 2015 12:23 AM
Location: San Francisco Bay Area

Re: WTB: M5 catalytic converter

Post by jhh925 »

Sorry, since you're not in CA, this is likely off-topic again, but here's my (lengthy) experience with the DEC unit for the M30-B35 that is officially "CARB Approved."

TL;DR: That DEC unit came with a stainless steel basketweave flex section in one of the downpipes. It turned out that there was no accordion section or any other actual piping inside that basketweave section. The likely result was that the flow of hot exhaust gasses was pulling in fresh air, causing the mix to be lean, causing the O2 sensor readings to be way off. The car wouldn't pass CA smog until we cut the basketweave out and replaced it with straight pipe. If you're not in CA and don't care, but the DEC unit (or whatever unit) you put in there has an open-air basketweave section, then the actual intake mix is likely to be always rich.
wkohler
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Re: WTB: M5 catalytic converter

Post by wkohler »

The M5 cat doesn’t have any of that.
Fanclutchnut
Posts: 14
Joined: Jan 05, 2021 8:32 PM
Location: Westchester Co NY

Re: WTB: M5 catalytic converter

Post by Fanclutchnut »

I was thinking the same. The flex section is part of the header on the m5.

wkohler wrote: Apr 10, 2021 3:49 PM The M5 cat doesn’t have any of that.
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