Well the "cat" is really a test pipe and since your car is OBDII you have an O2 sensor after the cat. Since that "cat" isn't actually doing anything you will foul up O2 sensors like mad. It's really hard to say how efficient the filter on that CAI is. At least it's a K&N knock off so it might be alright. But if you put that on all in all you'd probably gain a whole 3hp. :hs: