Should I get retuned?
make sure those are in-line with what was set dyno wise (you will need a wideband)
Likely the only thing that changed will be your Fuel Trims. I would have someone log it and see what the tune looks like
Yes, you have to retune it - it will be lean at midrange and WOT.
Customer swapped catback from Flowmaster to Hooker, both were full catbacks, tested on the same dyno and same day. The Hooker catback picked up right at 19.5rwhp over the Flowmaster exhaust. Crazy. The car was a 400rwhp M6 car.

