Mac 2005-07 Mustang GT 2.5" Pro Chamber w/cats for stock headers. MAC has done it again with the release of the all new ProChamber for the 2005-07 Mustang GT. This particular pipe works with the factory headers. This is a 100% simple bolt on for your 2005-07 Mustang GT. Most cars have seen gains up to 20rwhp with this simple bolt on. This pipe not only makes great power, but also sounds amazing! You owe it to your 2005 Mustang to bolt on a MAC Prochamber and make it sound as good as it looks. ** Please note this pipe DOES include catalytic converters. It is NOT an offroad pipe like what is pictured. We just dont have pictures of the pipe with cats on it.