Can I connect a 3" magnaflow catback to a stock cat, or do I need a 3" cat?

Reason being my catback is badly rusted and as I need an emissions sticker, it's going to have to be replaced. I just want to know how many parts I need to replace.

 

You could, but you'd most likely need a reducer between them. Not ideal, but it would get you by until you got a 3" cat. But even then, you'd just be moving the reducer farther forward.

Or instead of a reducer, you could cut short slices in the 3" pipe, then squeeze it down to fit & weld it in place.

 

I understand that it's not ideal...but we're talking about a relatively stock LO3. Eventually I'll get headers, y-pipe, and a full 3" cat, but until then I frankly just need a completely solid pipe from cat to bumper.

 

You can with one of these:



Should be around $10 at your local exhaust shop.