which O2 sensor are you talking about?

you want the front O2 sensor to be directly in the exhaust stream so the PCM gets a good read on the exhaust gas. so don't space out the front O2.

do whatever you want to on the rear O2. i'd leave it alone and only change it if does throw a code. if it ain't broke don't fix it.

 

I used the Jegs 555-31020 y-pipe. But honestly I wasn't impressed with the design for the money. One thing I didn't like was the joint where the two sides come together instead of swelling one piece to fit over the other they reduced it to fit inside the other, I felt this created less flow. I'm thinking about cutting that out and redoing it. Also maybe it was the headers that I used, but it just didn't fit like it should have, for the money spent I'd been better off taking it to a muffer shop.

 

You want the pipe reduced like that in the direction of flow. It helps with leaking when just being clamped. And that little bit isn't restricting squat anyway.

 

that little restriction you speak of champion isnt anything compared to the restrictions for the stock y-pipe/cat