i'm puttin a 2.5" exhaust on my cobalt probably next month and wanted to replace my dp too w/ one w/ a highflow cat but my buddy tells me that i should just go catless for better sound and hp. my question is my car is registered in IL but i live in KY(long story), and in IL you have to have emissions tests so i need a cat to pass, dont i? they dont do emissions tests here in ky but they'll give u a ticket if they pull u over for anything and realize u dont hav a cat but the loudness of the exhaust

 

ok major misconception! removing back pressure adds HP... not always... unless you have boost your motor needs some back pressure to help the head do what it's designed to do which is scavange air. If anything you should buy a DP that was designed to run on your car with your mods, otherwise don't do it. Your car without a tune will run slower, and make less horsepower with an aftermarket setup if you don't have a tune. Just get the LSJ downpipe and run that! it's a good size difference from the stocker and has a better flowing cat. If you just want the noise then buy a resonator, cut the cat out completely and run straight pipe. GOOD LUCK! don't suck a valve!