Air fuel ratio

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It depends on your current tune and A/F it is currently at. Every car is different. The mods in my sig, the a/f was okay until the headers and the o/r h pipe I needed to add 2% rich at wot. When I first install the headers and drove the car. The a/f was 13.2 at wot, which is a bit aggresive. then after added more fuel the a/f was 12.8 at wot. if that is all you r adding I would say that you wouldn't need to add more fuel. But like I said it depends on the current tune and where the a/f is currently at. Have you ever had the car dynoed? I would say that you are okay adding the x-pipe without adding fuel.

with the sct xcal2