I have a 04.5 Cummins that I bought with a 5 inch exhaust system on it. Several attempts were made before I bought it to quiet it down. The truck is LOUD period. In an earlier post I asked Chris if he had ever had done a dyno test with/without a 5 inch cat. He told me that he had not. I got to thinking about a 5 inch system on a 360 cubic inch engine. The WHY question kept coming up in my mind. I noticed that there is a real lag from the time the smoke exits the pipe after a nudge on the accelerator. This just means that the pipe is huge for the amount of exhaust gas coming out of the turbo. It is basically open to the atmosphere.
At any rate, after I installed a Suncoast torque converter, the drone really got bad. The new converter hooks up way earlier, and with more of a bite. So I decided to install a 5 inch Magnaflo cat ahead of a 5 x 50 inch Donaldson muffler. It is VERY nice. It is not stock quiet. It has a nice little growl to it and NO drone. and last but not least, if I go to a State that looks for cats n stuff, I will be ready for the emissions guy.