MagnaFlow Series™ Stainless Steel Cat-Back Exhaust System with Dual Side Exit (16523) by MagnaFlow®. Exhaust System Type: Cat-Back. Exhaust Tubing Material: Stainless Steel. Main Tubing Diameter: 3". Kit includes polished muffler. MagnaFlow systems give more horsepower and torque than factory exhaust systems by providing better exhaust scavenging and gas flow. They also provide the characteristic MagnaFlow looks and sound.