I have a jdm crx sir with b16, with rs*r header and 2.5" exhaust. The exhaust is terrible so i want to replace it and I'm wondering if i can go with a stock exhaust (mid-pipe/muffler) for crx si or if the pipe size would be too small for the b16 or cause a problem by down sizing after the b-series header?

Also on my exhaust there is a bung on the cat (on the mid-pipe side) with a wire that goes into the floor. What is this? both o2 sensors are in the header and hooked up.