I'm not sure this is the best advice. Infact it sounds like something I would have said when I was 16.I have a 1994 ford bronco and I cut the cats oped and took them out then welded them back. The o2 sensor on mine was before the cats so it didn't throw a code and I got better gas miliege. Just my 2 cents. I also had a 1995 mustang gt with the 5.0l and bought an offroad H-pipe with no cats and it didn't throw a code either. My experience has been as long as the vehicle is OBDI then it's alright.