Hooker comes with 1 bung you can have 3 more welded in(its really not that big of a deal) and its a crapshoot if you will throw a code or not so me do some dont. You can get O2 sims though and then it wont throw codes. This is if you want to get rid of your cats. If you want to keep them you will have to have to get a collector pipe and weld the exhaust back together.