On a dual cat set-up, do you need to find cats that are specifically made for a dual cat set-up or just get 2 normal cats?? I searched around the boards and found the subject mentioned in a place or two, but the question never got really answered. I would think that you could just rig up the system with 2 normal aftermarket cats, but I don't want to make a bad assumption and find out the hard way that they won't fit. I'm doing a lot of research and gearing up for an entirely new exhaust system ... headers, cats, and cat-back. But my 89 formula 350 has a factory dual cat set-up, which I have been told is more of a rare feature, and because of that I want to keep it as close to stock as possible with my upgrades. Plus the factory said it was good for 10 more HP, so I pretty much just want to keep it. But the dual cats make life a bit more complicated. The only header/y-pipe combo I have found that are built for dual cats is the Hedman #68491 package. The cat-back will be the Flowmaster Force II kit #17150. But that still leaves the cats themselves to figure out. Any ideas???

Catco 4153 is a high flow dual cat setup for the dual cat 3rd gens. Comes with the stock style routing system with Y-pipe. It's $375 from Summit.....On the other hand, a Catco 9118 (single cat, what I have) is only $148 from Summit.

Dyno Don makes single and dual cat Y-pipes for his header systems.

I appreciate modifying while retaining the stock type system layout. But honestly, nobody is going to be able to see the difference in your cats unless the system is up on a hoist. I like the keep it simple aspect of the single cat system.

Thanks, I will look that Catco set-up to see what I can find out about it. But what it is exactly ... like a cat-back kit that comes with the cats??

I already spoke with Dyno Don. His stuff looks great, but it doesn't come with an installation kit or step-by-step instructions and this is my first header install attempt, so I really need it to be idiot-proofed.

And I hear you on the idea that no one will see my exhaust set-up unless it is on a hoist ... but hey, I will know. Plus that could spark up a debat on whether or not the dual cats is really good for more power or not.

Any 2 1/4" aftermarket cats with the air tubes on the driver's side will work. There is not a "dual-cat" specific catalytic converter you have to use. Some companies make y-pipe assemblies that come with dual-cats, but they only work with the stock manifolds, and will not work with any headers.

Yeah, the Catco setups look they fit right onto the stock manifolds. Looks like a good deal and all, but I really want headers. So unless anyone can tell me that the Hedman package is crap, I think I am going to go with that.

But now I have another issue ... now that I can stop looking for cats specifically made for a dual cat setup, what should I be looking for in cats. I know the cat-back kit from Flowmaster has 3" piping ... so does that mean that I need to find cats that have a 3" outlet?? And I know that the headers have 2.5" collectors, so I am assuming that the y-pipe that comes with it is also 2.5" ... so does that mean I need cats that have 2.5" inlets??

Anything else I should be worrying about??

I'm not familiar with the Hedman setup, but if its y-pipe is 2.5", then yes you will want 2.5" cats. After the two cats, two more 2.5" pipes should join together into a Y that will exit as 3". That goes into your 3" Flowmaster.

Well, from the look of the diagram of the Flowmaster setup, it looks like it already has the y-pipe included that comes out the back of each cat and then comes together. I'm not sure if that section of pipe is 2.5" or the full 3" ... or anything else for that matter. But I was looking around different threads and saw something that made a lot of sense ... using adaptors. Wow, its always the simple solutions that are the best. For the life of me that never occurred to me. Its a good thing too because I wasn't finding any cats on Summit or Jegs that had a 2.5" inlet and a 3" outlet.

Here is a system made by Magnaflow.

"Burnout91" has one of these on his car, I modded the ends to fit my headers.

It is two 2 1/2" pipes into a Y but the y cones down to fit the stock I pipe.

I cut it back to where it is 3" and connected it to the 3" I pipe.

It works well on his car.

Does anybody know the part number on that Magnaflow system?? Does it fit right up a dual cat setup?? I would love to do something custom, but I just don't have the tools or the know-how to do it. My plan is to install headers and buy aftermarket cats and a cat-back system that I can bolt up myself and then drive to a muffler shop to have them weld it up.

Plus budget is a big concern ... that is why I'm thinking Flowmaster ... a little bit cheaper and hopefully I will get the sound I am looking for. But those polished Magnaflow kits look really nice too. Do they outperform Flowmaster or sound better ... enough to justify the extra cost????

Sorry, I thought the # was there ...#23479

Their cat back is way better than Flowmaster.

I should have looked at the thumbnail a bit closer before my last message ... so I assume this is designed to fit onto the stock manifolds and take the place of the stock y-piping and cats. From there I guess you would fit on magnaflow cat-back ... anybody know the part number of the kit that would fit on from here??

Will this fit onto headers or will it require a lot of modification??