So I have a 2004 Cummins 325 HO and everything is stock on it right now. I am getting a new CAI tomorrow and looking to order a new exhaust system. There is a local truck shop here that I'm getting an exhaust through and I was looking at MBRP 4" turbo back exhausts. The only questions I have though is that the system with the muffler delete pipe is about $275 and the system with the muffler is $500. Which is better, turbo back exhaust with or without the muffler? Do you lose back pressure without the muffler? I'm looking to purchase tomorrow. Or does anyone have any input on a better exhaust system than MBRP 4" turbo back? Thanks everyone