Did a quick search and could not find any info. My question is can I install ( without major mods) the later style dual cat system on my 1988 TransAm GTA. Is it worth the effort? Issue is that I would like to improve the exhaust system but I have to maintain a reasonable apearance of stock for the emissions testing. Engine is a 350 ci, vortec heads with an LT4 hotcam. Intake manifold is a Scoggins-Dickey TPI base with SLP intake runners.

 

HELLO.....
I did a similar upgrade.
The hanger for the rear of the dual cat system is different. Also you will need the 063 & 064 casting numbers exhaust manifolds. And lastly, the heat shield for the dual cat system is larger.When I smoged my T/A after I changed mine, it was not an issue. The smog tech didn't say anything and neither did I. Hope this helps
By the way, I am assuming that your dual cat system is a factory unit.
Bill

 

I put a duel cat Y-pipe on my 88 and didnt change or modify anything. if you get lucky and find an old G92 optioned car you'll have everything you'll need. I have an extra Y-pipe but no cats for it and Summit and Jegs sell after market ones that should bolt right up but again.....no cats. And like the other person said, unless you have the "Big" exhaust manifolds you'd be wasting your time. I really didnt see a hugh differance when I did it except the car did rev a lot quicker Good luck with your swap!

 

Thanks for the info guys. Looks like the Y pipe, with cats and the intermediate pipe are readily available ( Summit, Walker, etc.). I think I already have the better manifolds, car was originally an "F" motor, hi-output 305 TPI engine. Is this a correct assumption? Could not find a heat shield, so that will have to be a search item. Now I have to decide if it is worth the effort and money for about 15 hp. Car runs flat right now ( revs slowly), I believe that I have a trashed cat ( had a bad set of injectors and really bad valve guides), so I have to do something, just not sure which way to go with this.

 

What are you doing for the EGR on those vortec heads? You might need it for emissions but its possible to pass without it.

If you're going to change the exhaust, get a set of Dyno Don headers. the Exhaust forum and read all about it.

 

The intake has the provisions for the EGR valve and I have a valve installed. The design is supposed to use the external Corvette style EGR pipe from the exhaust manifold to the intake. Since the EGR valve is in place, it passed the visual and they dont do the sniffer test up here ( yet). When I had the chip retuned, I had them remove the EGR info. No check engine light or error codes. I will review the info on the headers. Thanks.

 

Are you running Dyno Don's headers? If so did you go with the single 3" cat vs. 2 cats?...not sure if Z28s had dual cats....my 87 IROC only had 1 cat.

 

Right now it is stock manifolds and a single cat.The more research I do, the more I am leaning towards forgetting the dual cat system and go with a pair of Dyno Dons headers and stay with the single 3 inch cat. Does anyone know if those headers will work with the stock 3 inch Y pipe?

 

Dyno Don is my father, of course I'm running his headers. My car came with dual cats, so yes I kept them. They're 2.5" Magnaflows. Dual cats came on all '89-'92 TPI cars with the G92 package.

No, no headers that I know of will bolt up to the stock y-pipe. Headers and y-pipes are a complete matched system and are made to fit with each other. You cannot mix and match them. Its my opinion that dual cats are worth it. You have 4 cylinders flowing into one cat each, instead of all 8 cylinders flowing into one cat. Yes its more expensive but I feel its worth it.