Here is the thing, I want to remove my cat and replace it with a strait pipe. I tryed to gut the cat but the bolts are seized and the only way the cat is coming off is with a hack-saw. I have already disconnected my AIR going to my header I haven't got around to removing the whole pump yet. Emmisions is not a problem so don't worry about that. The question I have is, What size pipe do I need to slip right over the exaust tubing? I think it's 2 1/2in. but not sure. Second: Will I throw an engine code or stay in closed loop mode because I am getting no reading from my cat? Third: What kind of headers do I get since I have no AIR running to them? Any info will help and thanks to all that reply.

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88 Firebird Formula
350 T.P.I. (Stock unfortunately)

 

You could have an exhaust shop enlarge the same size pipe for your y to slip over and weld it to the old cat to i pipe connection.

There are no sensors in your cat, so you couldn't possibly get any engine codes or have any drivability issues, the cat has absolutely nothing to do with how your car runs.

Just buy any headers without air provisions, most major brands makes them. You may want to get some with an o2 bung though, or have one tapped. They are much cheaper than smog legal headers.