piped-imo I like a muffler because a v-8 diesel motor sounds stupid straight piped. all of those with the exception of the 09, I ran 3 1/2 inch with a y pipe with 2 flomasters turned on there side with turn downs. they sounded great. on my 6.4 I have a full 4" with a resonator on it. It isn't that bad. nice deep sound to it.