They do not work right with the 01+ cars, you have a chance of the car going into a cycle of just dumping fuel. Cheepest way to fix your problem is remove cat and have a strait pipe welded in and run the spark plug non fouler. For more info just read this thread http://www.grandprixforums.net/showthread.php?t=7092
On a side note you can get a cat for >$80 from some of the vendors. http://shop.zzperformance.com/store/...onverters.aspx