High Flow Dual Cat w/SSIs and 2 in 1 out?

[RSBob]

Have an 82SC which I want to backdate the exhaust to SSIs going into a two in one out with two high flow cats in between. Why? Because if it's possible that would make me happy and isn't that what it's all about? (If you want to tell me otherwise, please feel free to put a sock in it.)

Any one done this? I have seen something similar with 2 in 2 out Monty but instead want to use a Dansk Sport.

Now fess-up y'all.

[Iciclehead]

Haven't done it as I have not gotten that far in my project yet, but have the new SSI's all ready to cut up.

I was planning on taking out the "S" shaped collector on the SSI's and either modifying a 2 in 1 out muffler to take the exhaust a little outboard of the stock location or fabricating an exhaust a la the picture below...



Only issue I have is finding a pair of cats that are small enough to fit the space....shouldnt be the end of the world as each bank is only equivalent to 1.7 litres, so there should be a lot of 4 cylinder small cars with a cat with enough capacity.

Dennis

[Arne2]

I see no reason that wouldn't work well, Rick. I've also seen pictures where someone welded cats in place of the SSI stingers. Once done, you should be able to use ANY 2-in muffler.

[tirwin]

Craig_D has done it.

Here's his thread where he explains it:
Craig_D's Dual Cat SC Exhaust

[RSBob]

Arnie, that makes me feel much better. Appreciate it

Looks like Craig thought it out really well with great execution. It appears that the size of the cats relative to the heat exchangers force them a bit outboard, can the pipes be successfully routed back to mate to the 2-in since I have a SS Dansk Sport (2 in one out) sitting in the garage? can Craig's modifications be made to work with it, or would the Sport need to be modified to for the two in part? Hard to tell how much room there is.

AND the million dollar question: I have read that adding SSIs and a free-er flowing exhaust can add about 15 hp. Will the free flow cats rob it down to 10? That would be a chunk-o-change for a gain of 10.

[Arne2]

After looking over Craig's thread, it looks like it would be difficult—if not impossible—to get the outlets back into the correct location and spacing to connect to a normal 2-in exhaust.

[tirwin]

I agree with Arne2. I think you'd have to do something like the Magnaflow he used to have room to route the outlets from the cats.

Regardless of how much extra hp the SSIs provide adding the cats will reduce it some. How much is hard to say short of comparing dyno results.

Adding SSIs may not be cheap, but it is probably the cheapest hp improvement you can do on an SC. Well, short of lightening the car.

Speaking of lightening... Craig's setup could be lighter than the stock setup. Hard to say just by looking at pictures but it sure seems like that might be the case. Just something else to consider .

[rfuerst911sc]

Thinking outside the box can the cats be fitted in the muffler ? Would be very stealth.

[Craig_D]

Hey thanks guys, I did do a lot of thinking and mocks before making my system. The dual Cats are very high flow Magna Flows and were the biggest ones I could fit in there. My guy, Hank Padilla, talked me out of the smaller ones, saying that they wouldn't last, and wouldn't flow as well as the bigger Magna Flows.

Although I haven't tried the setup without the Cats (with track intermediate pipes in place of the Cats), I can say that it flows very well and my 911 came to life with this muffler/Cat combo.

The system is also much lighter than the two in/one out muffler.

In my thread, you'll notice that I created two versions. The second muffler version was two Hush Power mufflers stacked and criss-crossed. This system had absolutely no drone, sounded great, but it looked like regular twin exhaust, so I went back to my Magna Flow muffler with it's drone at around 2k rpm and it's rally look exhaust outlets. I have an end cap in the mail from Hank as we speak, to solve that for commuting. I do have that custom Hushpower dual muffler, if anyone wants to take it off my hands and put some Cats onto SSIs.

Anyway, the Dual cat system IS possible, does pass emissions, does flow very well, is light and sounds ridiculously good.

If you want to ask me any questions, I'd be happy to help.

Cheers,

- Craig_D