Just got my Aero Turbine installed on my '01 5.4L. It's a 3030 which is 3" in and 3" out. It has a Y pipe going from 3" to two 2 1/2" tail pipes out the back. The sound is great. Nice deep sound when your in the gas, then it's really drops at cruise. The truck to me has a better sound with this one over the glass packs that were on the truck. We'll see if the mpg changes. To me the sound is better than the flowmaster or magna.