a full exhaust system is always better (long tube headers, no cats, straight pipes). You can pass emissions with no cats if you get ur car tuned. I have an '05 Mustang with 2 cats (both removed) and I can pass emissions (i dont need them cus i live out in the middle of nowhere). When you get ur vehicle tuned you will get MANY things. You will have more power than just bolting shit onto the car, you'll get better mpg (usually) and the tuner will basically tell the computer: "hey...there are no cats...dont worry about them" so u wont have a CEL.

ah...so many ways to beat the EPD. lol


ORRR what I am going to do. Put headers on ur car, 2.5" or 3" cutouts before the cats and keep ur stock exhaust system.