BigDaddy

what buttercup said about the cats is correct for an ideal system, where the catalysts are 100% efficient. However, we know based on past emissions tests, that there are in fact Nx, HC, and CO emissions that are measured out the tailpipe. This indicates that the catalysts aren't removing all of the emissions. A second catalytic converter inline should help further reduce, and oxidize remaining emissions. It should be noted that the second converter would actually be removing fewer emissions than the first, so two converters would be better than one, but not twice as good.

Buttercup

Find out if they are all 2-stage cats or not though. I'm interested to see if both cats oxidize and reduce the exhaust gasses. If they have the front set of cats reducing and the last set of cats oxidizing than it supports what I was saying (thinking out loud ), if not than running two-stage cats in series might help clean up the tailpipe!

I believe that some C5 Corvettes also used multiple sets of cats, btw. Again, I don't know the specifics on the cats themselves though

Dr.Mudge

Cobras had 6 cats, at least when I had one.

Good point about the light off, with running the car hot I think it would work, but you could always hack up your exaust closer, and put some flanges there.

or just bite the bullet and swap cams.

speedmiser

I've yet to have a tech crawl up under my car and check for cat placement. 4th gens are little low slung - most of the inspection people dont want to crawl on there bellys to inspect your exhaust piping. As long as it passes the sniffer, most any arrangment you have will be fine.

Z95m6

I don't know if anyone on the mustang site will know if the cats are two stage ones. I am sure almost nobody on this site knows what kind of cats are on our camaros, they probably just think a cats a cat.

Z95m6

I figured i would bump this back up and see if anyone else has any ideas.

Dr.Mudge

I've seen the info somewhere, I am pretty sure we are 2 stage cats not 3, but again I unfortunately dont recall for sure. The info might be on Christian's site.

Z95m6

can i ask dr. mudge who christian is?

Buttercup

Christian Millard, Crutchfield employee, and LT1_Edit extraordinaire

We have 2 stage cats, but I was more interested in what type of cats are used on the multiple cat H/Y Pipes.

Z95m6

do 2 stage cats work better than a single stage? Would it be more efficient to put a dual stage cat in place of the stock one and put the other dual stage cat right at the front of the cat back.

Buttercup

Go back and read my first couple of posts for a better description of the stages.

The stock one IS dual stage, federal law mandates it. One stage eliminates NOx emissions (reduction) and the other eliminates hydrocarbon and CO emissions (oxidation)... hence they are 2 stage. It's basically two different cats in each catalytic converter.

What we (I) don't know is IF you can use two stage cats in series. That's why I was asking about the mustang setup with multiple cats. If they have two stage cats one after another than it must work. I didn't think you'd want to put a reduction catalyst after an oxidizer catalyst but I could easily be wrong and the Mustang could prove it.

Z95m6

well i may find out the answer in the future because i have done decided i am going with the 230/236 on a 112 and if emissions hits which it is doing in so many other states i will be forced to find something that works.

nateh

Our cars have 3-way catalysts. The 3-way notation means that the brick can catalyze HC's, CO, and NOx. A 2-way catalyst is an oxidation catalyst, effective against HC's and CO only.

The precious metal loading (Platinum, Palladium, Rhodium) is the same along the entire length of the brick. There aren't any "stages," though there has been some activity in that area of research. So, to answer Buttercup's question, the oxidation and reduction do happen in the same catalyst. They happen in response to whether the exhaust stream is oxygen-rich (lean) or oxygen-poor (rich) in that instant. To oxidize HC's and CO, you need a leaner condition, and to reduce the NOx, you need a richer condition. Since both happen in the same space, the mixture is constantly adjusted via the O2's to change the amount of oxygen present in the exhaust stream. This is why the O2 sensor voltage varies rapidly within a set band.

Given the above, you can see why an AIR pump works. At startup, an engine likes to be run a little rich, which enables the formation of HC's and CO. To oxidize these, the catalyst needs to see a leaner condition, so if you pump a little air into the exhaust stream, it gives the catalyst what it needs to oxidize the HC's and CO. With the AIR pump, the engine can run a little rich on startup, and still meet the emissions requirements.

The reason that Fox bodies have more cats is simply because they put out more pollutants. Kind of like a second filter (If the first one isn't enough, let's add another.). This isn't unique to the Fox platform (SN). Most of the passenger cars Ford made at the time, from the CD car (Contour/Mystique), to the D car (Taurus/Sable), to the Explorer, had extra catalysts to meet emissions requirements. Most of the time, the cats were in a small light-off/large underbody configuration. The first cat was small and as far forward as possible to minimize thermal inertia and heat as rapidly as possible. The large underbody cat did the "heavy lifting," so to speak.

I'm not a programming expert, but considering how a 3-way catalyst works, I've wondered if the program can't be altered to change the mixture enough to make cars with more aggresive cams pass the sniffer. Just thinking out loud on that. I'm sure it would take some testing to find out.