I have a 97 cx with an LS swap and a stock exhaust, with no cat. I just bought a new 5zigen exhaust to replace everything with, and I want to plug in my o2 sensor because my check engire light has been on for a while. So what should I tell the guys at the muffler shop to do when they weld it all together? Should I put the new o2 bung on the last part of the 4-2-1 header? Should I have them weld the flex pipe into the new exhaust or have them put some flanges on the flex pipe and attach it?

 

have them put flangs on the cat: makes it easier to take off and keeps its it simple:

also, put the bung on the cat: if your sensor reaches, it should: just in case your cat dies or fries: its simple replacment: and doesnt mess up the catback