What are the advantages of deleting the cat. conv.? I ordered a 4" exhaust turbo back, but it uses the factory cat. which is a 3" i believe. So if i'm putting a new 4" pipe,:dunno: it has to taper down to 3" factory cat. seems like i'm defeating the purpose of a 4" exhaust. need to get a cat delete pipe right? what about inspections ? put her back on? for that. am i thinking right?