I Just picked up my Ford Racing 3" cat back (M-5230- M55) yesterday and put it on last night-- and took it back off today !! It was so loud I could not believe it was a Ford part. I know they say it may be "objectionable" in some applications well let me tell you they ane not kidding. I can honestly say I have not heard a cat back on a mustang that was louder than this one and yes I still have the stock H pipe on the car. It did seem to add power to the top end of the rpm range. I also noticed that although the mufflers are the oval type and look just like the stock ones you can see straight through them !!