Performance exhaust systems are available in multiple sizes. The most common is a four-inch, these are designed for vehicles creating less then 450 horsepower. Larger diameter exhaust systems such as five-inch, are typically recommended for vehicles creating greater then 450 horsepower. Performance exhaust systems increase exhaust flow by eliminating the restrictive stock muffler, replacing factory crimped bends with smooth mandrel bent tubing, and increasing the overall pipe diameter. The benefits of increased exhaust-flow are reduced EGT's(exhaust gas temperature), increased horsepower/torque, fuel mileage gains, and a deep throaty sound.
Attention 2004 Model Year Owners: to ensure that you have a 2004.5 Dodge Cummins "600" 5.9L Diesel you must check the engine tag or build date. The engine tag will be located on the front engine cover or valve cover. It will display a rating of 325 HP. Otherwise; you can check the build date which is located in the driver's side door jamb. If the truck was built in 04 it will be a 2004.5 "600" Series. If it does not you most likely have a 2004 Dodge Cummins 5.9L Diesel.