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. Large diameter exhaust systems such as five-inch, are typically recommended for vehicles 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 in exhaust-flow are reduced EGT’s (exhaust gas temperature), increased horsepower/torque, fuel mileage gains and a deep throaty sound.