2014 Cruze Diesel

Your vehicle is tuned to have a certain amount of back pressure. Hollowing out the cat, however, will have a minimal effect on engine power. If you decide to remove the catalytic converter's inner mesh, you will encounter a check engine light for a failed catalytic converter. You can fix this by buying a 90 degree O2 sensor spacer, and installing it along with the sensor on your downstream (after catalytic converter) O2 sensor socket.

Oh, and fun fact, engines don't need back pressure. That's a myth.