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 an early 2004 Dodge Cummins 5.9L Diesel you must check the engine tag (A Red or Silver Tag) located on the driver's side of your engine. The tag should show a horsepower rating of 305. If it does not you most likely have a 2004.5 Dodge Cummins 5.9L Diesel.