My 91 gta has the stock exhaust on it and I've been looking around for an aftermarket exhaust and everyone I find is for a single cat back exhaust. Mine has two cats. Does anyone know where I can get an aftermarket exhaust for my dual cats? And what headers would fit my car (it still has the smog pump on it)? (should I delete the smog pump?)

 

Best bet would be to just scrap the two cats in favor of a single cat system. I think SLP used to sell a two-cat system but not sure if it is still in production.

As far as headers go, it's up to you to decide which ones you want because you have a lot to choose from. Most people here recommend Edelbrock, Hedman and Hooker headers (Hooker's 2055s seem to be a board favorite, and for good reason). Flowtechs are generally frowned upon because they suck; SLP has the only 1 3/4 shorties for our cars but they are expensive. I'm not sure who else sells headers but those are the five main choices you have.

 

The cat-back portion is virtually the same. No problem there. It would be no problem for a competent shop to fab one up or make one out of a single cat system using your existing for a model. You will loose potential power going to a single cat.

 

Edelbrock and Hedman make headers with downpipes for dual cats (isn't really a y-pipe with dual cats).

 

I always hear about power increases from going to a dual cat setup from a single cat system, but I have yet to see any legitimate dyno graphs that prove it. On the other hand, I've yet to see proof that it doesn't increase power either.

The catalytic convertors of the 80s were far inferior to what is being produced today. I believe GM incorporated dual cats to improve power with the technology they had at the time, but it may not be necessary anymore considering all the high performance parts available in this day in age.

 

Maybe, but seems to me two current technology cats would contribute less of a restriction/power loss than one current tech cat would....

 

Well I'm going to knock out the cats anyway but I just really wanted to know if there was anyone out there who sells a cat-back sys for a car with 2 cats. I'd heard that flowmaster is a good one for the money. Should I get that or maybe put electric dump offs on my car? would they give me more power (dump offs) or work against me because of back pressure?

 

By "knock out the cats", do you mean you're going to remove them, gut them, or what?

If you're going to replace the cat-back and do something to defeat the cats while you're at it, you might as well get Hooker 2055's, get a cat-back for '86-'90 TPI single cat application, and put a piece of 3" straight pipe between the y-pipe and cat-back. Whether dual- or single-cat, the 3" cat-back is going to be the limiting factor, anyway, and if you aren't running cat(s) for emissions reduction purposes, do it the smart way and get what I suggested above.

Whether Flowmaster is good depends upon to whom you are talking. I know mine is louder than I'd like, and I can believe it when people say their mufflers are more restrictive than others that are available. Cross flow mufflers are probably in general less efficient than straight flow designs. So, I'd say do more research before you conclude that Flowmaster is the way to go - especially since the discussion started off with dual cats to begin with.

Having said all that, the Flowmaster 17150 is a dual-cat, single 3" outlet system. $240 from summitracing.com (flo-17150). The 17151 is a single 3" inlet (at cat outlet), single 3" outlet system same price.