I figured I'd put this request in its own thread, since my prior requests might have gotten buried in other discussions.

Who is this addressed to?
Any M56 or Q70 & Q70L V8 owner who has had primary catalyst issues and is planning to have them replaced.
I suspect a time is coming for Q70 owners to start having these issues as well. For now, it's the 2011-2012 owners, but the issue might be coming down the line. The same part is used throughout the generation.
Driver side: 14002-1CX0A
Pass side: 14002-1CX0B

If you are planning to get yours replaced due to those codes listed above, I would like to get in touch and get your used manifolds for research purposes.

Projected Outcome?
First, I want to figure out WHY the codes come up.
Secondly, I want to come up with a solution that hopefully does not require manifold removal from the engine.
Finally, depending on the issues at hand, I might redesign the exhaust manifold.

Core charges, etc
If your installer wants to charge you a fee for you to retain these manifolds, let us discuss what these charges are, and I will cover them.

Shipping & Handling
If you can retain the original packaging that comes with the new parts, that would be great.
Otherwise, just take them in to a FedEx/UPS store and I'll cover whatever they charge to pack & ship to me.
I am currently located in the St. Louis Metro area, but I'm very mobile. Let's discuss.

Payment
I have PayPal, CashApp, Venmo, Zelle, and can pay cash in person if it happens to be a local pickup.

Contact Info
The best way to reach me is by email. EdBwoy AT gmail.com

***
Please share in other circles whose members might be affected or be able to help.

You're a good man, no matter what anyone else says about you . I'm getting closer and closer to having to have to do this so if I can get my cats back for a small fee (or free), I will certainly send em your way.

I'm also going to post this thread on the two M groups on FB.

Haha, thanks Ilya, you're a standup guy.
See if I were closer, I'd even be up to helping you with the labor of removal & installation...if you guys still have the lift.

Yep, we still have it lol. Best money we ever spent as guys in my family lol.

I have been following the whole manifold replacement issue for quite some time. I've been sitting on the fence since my first P0420 at 95K miles. I'm at 112K now, and still running with intermittent P0420 codes. From what I've researched, a brand new cat is 99% efficient then drops to around 95% after 4000 miles or so. I know when I had my Acura MDX converter replaced (under warranty) years ago, the tech told me that most manufacturer's thresholds are around 92% which is the 3% drop that I had mentioned before the DTC code P0420 or P0430 is triggered. The LEV (Low Emissions Vehicle) requirement allows only 0.225 grams/mile of hydrocarbon which is squat in reality. PCV vacuum leaks can also contribute to the DTC. In my case, a slightly cracked drain valve in one of my catch cans was the culprit.

I read the post from Brandengonzo on how he changed the bank 1 manifold by unbolting and removing the steering column, unbolting sway bar and removing the driver's side motor mount, etc. by supporting the engine, as opposed to jacking the motor/lowering the fame. I crawled under the car and had a look at the job he described. I believe this would be the way to go IF you have a lift at your disposal. There's no way to do this in a garage laying on your back...so that DIY option is out in my case. I'm curious as to how much his shop charged to do the job in the way he described. He hasn't posted any updates since. I may talk to my service advisor about this and get their input.

So I am at a crossroad on this issue. Since my car is running great (other than the intermittent P0420 DTC) as long as I am passing NC emissions, I am reluctant to replace the manifolds at this point. Yes I am being a big weenie about this but I know that at some point I will have to do something. However, since I plan on keeping this car long term, I agree with Ed about finding a solution that does not require manifold replacement. The space is so tight that I believe using the OEM manifold headers would be the best option. First of all, I would do both banks if I decided to pursue this, since the existing manifolds would have to be removed anyway. I propose separating the catalytic converters from the headers after the AF sensor ports, and welding down pipes in place, cutting the flanges off of the cats and welding them to the exit ends of the down pipes, maintaining the factory flange orientation at the point where the secondary cat/mid pipe would bolt up...basically headers. Once those are reinstalled, either install the new cats in place where the secondary cats would normally be, or let the secondary cat/mid pipe become the primary cats if you're running stock exhaust. If you go this route, you'll have to install O2 ports behind your secondary's. Either way, only issue is the O2 sensor wires reaching the ports since they would be farther downstream. I don't think there's enough slack, so additional wiring may need to be spliced in. Once this initial work is done though, subsequent cat replacement would be easy.

If you don't want to reuse the old manifolds, buy new ones, use the old ones as templates and modify the new manifolds with downpipes, and use the new cats for the duration. They will have the O2 ports already welded in. Then going forward, you can buy aftermarket cats. Personally if I was going through the trouble of removing the old manifolds, I would go with new ones. Anyway, just my thoughts. Only other option is to go with custom headers. In my area, Kooks in Charlotte, NC will design and install headers to fit. Initial cost will be high, not sure if it would be worth it IMHO.

Ok so i have a 2012 Infiniti M56 that has a catalytic converter issue as well that didnt start having issues until about 155,000 miles and need to get it replaced BUT REALLY Pricey... so im saving money to replace that.. but the crazy thing is that the only major thing wrong with my car. Its been a amazing car..