Car is a 91 z28, l98 auto, dual cat car, SLP TOTL cat back. 228k miles

It all started when one day I started her up after work and the exhaust sounded like rocks bouncing around in it. I called an exhaust shop and they said cats are probably clogged. So I limped her home. All the way she was weak and I could hear the exhaust coming out at the cats. I get home and pull into the driveway. A good size leak has popped up at the front of one cat and to my surprise I look down behind my car and notice a weird looking rock. Turns out its a piece of the inside of my cat (I have no idea how it got out)

So my plan this weekend is to cut the cats (they're welded in) and replace with test pipes.

My questions are:
1. How long are my stock cats??

2. The owner of a local muffler shop looked under my car and said its 2.25in piping before the cats. But after searching on here I hear that 350tpi dual cat cars got 2.5in cats. Which is true??

3. What do I do with the a.I.r piping that is in the existing cats? Can I just let it pump air open??

Thanks guys!

 

1. take a tape measure and find out.

2. cut the cats off and measure the pipe (assuming this isn't your only car?) or get a section of 2.5" and 2.25" pipe and then just return whichever you don't use.

3. pretty sure you'll have to bypass all your smog and emissions junk once you take the cats off.

you could just replace the catalytic converters though.

 

not sure what state you live in, if you live in a state that has motor vehicle inspections, I would just replace the converters, if you don't cut them out and measure the pipe buy pipe and have new pipe welded in or make sure you clamp it good so you don't get exhaust fumes in the car

 

The question you should be asking yourself is what condition caused the cats to get clogged? It is usually due to the car running extremely rich. For you to notice a difference in such a short period of time it probably started running poorly recently.

 

I do have yearly inspections but they never look under the hood or under the car. Hell, I just passed with no high beams lol.

The car had an issue when I bought it where it would choke out and stall at random times. Turned out to be tps related. So it ran rich for a while but now I have no issues other than the cats. Plus the car has 228k miles..

And the only reason I hadn't measured the cats myself is its been raining for 3 days. The ground is to soft around my house to put the car up on ramps. I thought somebody may know the length off top of their head.