I just got my 94 Z-28 automatic up on a lift cause I heard a rattling noise from underneath the car. Turns out something in the cat is broken and rattling around, probably some of the catalyst wafers inside. The cat is connected to the Y pip making a stock new one too expensive to buy. so emmissions problems aside, should I hollow out my existing cat? Should I dump out whatever is broken and keep any good wafers inside the cat? Or should I buy an aftermarket one and weld it in place of the old one ? Has anyone ever tried any of these options? What are some problems with too little back pressure or too much? Any suggestions would be great.

 

Gut the cat. The catalyst is not a series of "wafers". The catalyst is a honeycomb brick. It is quite tuff and hard to get out. No problems with lack of back pressure without a brick ,the stock gutted y-pipe provides way too much.

 

If that happened to me and I had your car I would rip the GUTS out the cat and if Emissions is an issue....at time of Emissions I would just get a highflow random tech cat and have them weld it in and after that your all good. Save money now...pay later kinda thing.

 

I just pulled my manifolds and cat off, and my cat was already gutted - meaning it self gutted after all these years. Funny thing is, I never failed emissions! So I put in a 3 in pipe to replace said cat. Haven't tried to pass the new setup yet.

 

Yes, your cat is bad. That same thing happened on both my Zs. I would recommend replacing it with a carsound unit. (ebay ~$35-$40)
Gutting it will make your car louder, but it doesn't sound good in my opinion. So if you don't want to replace it, at least replace it with a pipe.

 

Thanks for the advice, I guess I'll just pull off the y pipe and rip the guts out of the cat. I wonder where the rumor that ripping off the cat could screw up your engine came from. Maybe other less restrictive cars get ****ed up by pulling off the cat.

 

I heard some where that all converters are warrantied up to 88k miles due to federal law, might check in to that.

 

really where did you hear that, my converter only has 85,000 on it.

 

A little humble advice: completely gutting your cat will make a "hollow" sound to your exhaust note. I tried something that worked pretty good. Rather than gutting it completely, just make a hole through the catalyst the same diameter as the in-pipe to the cat. Basically you're making a straight-through muffler and it doesn't have a hollow sound at all.... at least on my car with the MACs and Hooker cat-back it doesn't. It made the note deeper and it pulsates harder. Sounds very clean with no rasp.

I also thought about just putting in a good stock cat(or high-flow cat) and dumping it before the axle like a single-shot design (getting rid of the cat-back). A buddy of mine did this with his 97 Z71 and it sounds awsome. No popping and one of the deepest/cleanest SBC exhaust tones i've ever heard. Saves a little weight too.