I ordered these cats because my passenger side cat needed to be replaced. An OEM cat was going to cost an eye-watering $1623. I figured that I could save some money and simultaneously get a performance upgrade. I have an Invidia Gemini cat-back exhaust and stock headers. I don't know if any additional power was made, however, my exhaust is a little louder than stock. Installation was about as easy as it could be, build quality is great, and no CEL.