I am running lt's no cats, custom y( by myself, dad), into a single 4 inch pipe. As far as hp, like said a 3 inch set up(single) will support a good bit of hp..

 

Nice set up !!I would like to tap my headers like that but iam using my 02s'...iI dont see any 02's i guess youre using SD tune ...looks good !!

 

again this is all procharger related...just got off the phone with Aerochamber and they say that aerochamber mufflers flow around 450CFM ...I dont know how much free flowing cfm is needed to not cause too much back pressure on the Pro...I will call them when they open at 900 am

 

Any additional info found through your research or trial and error?