In all fairness I'm not too sure. I am only using it to go through an MOT and it will stay in the car if ever needed.

With a traditional 2 box system they tend to be fairly free flowing. This reduces the output diameter to 2"

I will not be driving it hard with it fitted - I would make my own and modify it if I had to retain one so as to get more flow. This will make it louder but this thing has seriously quietened the car down as it is.

I have seen them on track days but not took too much notice.