Hey, I have a decat pipe fitted and was wondering where the best place to mount the o2 sensor is? The car only has 1 pre cat o2 sensor and the pipe has room for a 2nd further down. Would it be better further down? Also is it crucial to have it mapped in? I'v jus started tweeking it but don't wanna remap till I have some other parts ready. What other bits can I install that don't require a map straight away.