I have a 2011 2SS/RS L99. I had some FLOWMASTER 40 Series installed and it made a bit of a difference in sound. Decided I wanted a deeper/louder tone, so I had the resonator removed and had straight pipes from the cats to the 40 series. No crossover pipe. Night and day difference in sound. I recommend you keep anything you remove or change out on your car just in case you want yo go back to stock for whatever reason.