My 2002 7.3 did not have a cat so I removed the muffler and went with a piece of stright pipe and I regret it horribly. I have actually ordered a muffler because it is so bad. When idling it sounds awesome. Sounds just like the big block sound. When accelerating you hear a ton of turbo whistle
. Bad part is when accelerating it has this horrible sound like it has dropped a valve or something. The sound could also be desibed as a V8 only running on like 6 cylinders. It is horrible. The sound is not so loud. Actually inside the truck I do not even hear a difference. I actually noticed a decrease in fuel economy believe it or not. I was getting 15.5 mpg on the interstate at 80 before removing the muffler. After removing it I only got 15 mpg at 70. Now that part really sucked. I am not sure if not having backpressure will affect the diesel in the same way it will affect a fuel injection gas motor but it sure seems like it did. Oh and the power seems like it has more low end and pulls hard through the rpm range but it doesn't seem to climb rpm's near as fast as it did. Now maybe there is an underlying problem with my truck that is causing it to be this way but it ran perfect before taking off the muffler. Just keep your stock muffler incase you want to put it back.