[decipral]

I eliminated the CAT but kept the Exup. So I can't really answer your questions with certainty. I chopped the exhaust and used the GSXR muffler tip, I kept the O2 sensor, exup and am running the Arrow tune and the bike soiunds and runs AWESOME!

 

[decipral]

From my understanding, if you removed the O2 Sensor you will more than likely get a check engine light. The CAT is easy to removed without issues and the Exup is prettty easy as well but need the right tune to go in. My arrow tune disables the EXup anyways so it is open as long as the bike is running.