I'm not trying to make my PZEV into a rally car, but I want a smooth ride with good performance for the street. I live in CA and I was wondering if I would have problems later on with CA's smog checks if I change the exhaust system of my Focus. If I will, then what can I do to change my exhaust's look and sound? My knowledge of cars is slim to none, and I was wondering how muffler's work and if I can install one on my own and which mufflers are suggested. Thanks in advance for your replies.