OK, I have an 89 Iroc with an L98. Single cat.

I'm planning on bolting up headers soon, and I was wondering if I should bother switching to dual cats.

I know that I will lose some power by not switching, but is it really worth it? I'd much rather put the money somewhere else. I'd think a single cat with a 3" out is pretty good, but whaddya'll think? Most of you guys are running single cats right? Isn't there some law about if it wasn't offered from the factory with duals, you can't put'em on? I mean, alot more f-bods were made without that option, yet tons of you obviously run headers, right?

...something like that I think.



Thanks for the insight!

 

i wouldnt bother with dual cats. run a 3" mandrel bent y-pipe into a 3' cat and you will be fine. a cutout before the cat would be a great option to pick up alittle more power.

 

The bad thing about the single cat design is the y-pipe, its more like a t-pipe. Since you're replacing that with the header install, it'll be a lot better.

I wouldnt run a 3" y-pipe. I think you meant a 2.25" or 2.5" y-pipe to a 3" exit, right?

 

exactly.

 

For what its worth when the factory switched from single to dual cats (1990 ?) it added between 10 and 15 hp.

RP.

 

yeah the dual cats helped alot, i plan on buying high flow ones when i redo the entire exhaust some day

 

how do you switch from single cat to dual?
what would i need to get?

 

i was thinking about that too. i plan on doing full exhaust (headers thru tips) in the fall. i was thinking if i'm redoing everything, will it really make a difference if i have two 3" cats instead of one? i have 2 cats right now, but they're stock...

anybody know for sure?

 

Yeah, see, you guys are asking the wondering the same thing I was. Sure GM said 10 HP, but come on....did it really?

Don't get me wrong, I'm sure it'll help, but first you have to buy a second cat.....and since you're they're you might as well replace the stock one with 2 HI-flow cats. That's money...even if you get'em cheap. Then you have to mess with the "cat-back" to go 2 cats into 1 intermediate, which at the moment, I wouldn't have to do. I would rather put the money into a cam or something like that.

For a mildly modded TPI, I would imagine that it isn't required. That isn't to say it doesn't help. Of course this idea could be wrong....that's why I posted.

 

Oh, and NJITIROC....

First, I'm petty sure that if 2 cats were not an option on your car(G92), then you can't legally put them on. I'm not sure which years it was an option.....(anyone)....?


If it was an option, then you need 2 cats of course....and the 2 pipes that go from each manifold/header to each cat. Then you need a 2 into 1 pipe from the cats to your intermediate pipe. It 's a lot of crap/labor to pay for if you don't weld. Hence the point of this topic. I'm hoping to buy headers and leave the "cat-back" alone.

 

I have a 305 that makes 230hp from the factory ('91 Formula). The exhaust is dual cat and 3 inch tube to hi-flow muffler. According to my last dyno run I am now making 260hp with a few simple bolt-ons pullies and Jacobs Ultra-Team (who needs a 350 eh ?).

I am convinced the dual cats and hi-flow exhaust are a significant contributor to my car's dyno numbers. I had an '88 with single cat that I upgraded to 3 inch but I'd rather have my dual cats -- later I can upgrade these to dual 3 inch that ought to prove interesting.

Converting from single to dual won't be that straight forward though -- you will need to build a splitter for the A.I.R. system to run to both cats. The two into one piece from the cats to connector tube can be picked up at any OEM source. If I had the choice I'd go with dual cats.

adious,
RP.

 

Couldn't you just use 1 cat with A.I.R.? ...and leave the other alone?

Does that make sense?

 

Good question. Not sure if you need to feed both cats with air ? I'll bet you do just because it would be too easy otherwise (some variation of Murhpy's Law). You know how these things work...

RP.