With the larger cells and fast exhaust flow rate, it is smooth, durable and do not have refractory wool burn-out problems. The higher the number of the cells, the smaller and denser the hole is. The higher the back pressure, the more it can enhance torque performance, while the opposite is true for increasing horsepower. Converting your stock catalyst converter (400~800 CPSI) into the Fi Exhaust metallic catalyst converters will result in significant enhancements in airflow discharge that circumvents the limitations and parameters set by car manufacturers.