[carsonmx114]

by breaking the insides of the cat the rest of the way out you will be knocking the pieces that are rattling around out, so you will have a hollow pipe left. if your car is exempt from emision you could have a muffler shop install a piece of straight pipe in place of your cat. the only advantage to hollowing out the cat is you have the apearance of having a cat on the car, since your exempt it would be less trouble and less expense to just remove it altogether.