I am currently building a very stout small block motor for my camaro. I need to know what size pipe will not restrict it. I currently have dual 2.5's into one 3in. I know the 3in is probably not enough, but is the dual 2.5 enough? Also, does anyone sell just the 4in intermediate pipe, not the whole catback? I contacted mufflex and they said they would not sell just the intermediate pipe. Thanks