MagnaFlow Series™ Stainless Steel Cat-Back Exhaust System with Single Rear Exit (16834) by MagnaFlow®. Exhaust System Type: Cat-Back. Exhaust Tubing Material: Stainless Steel. Main Tubing Diameter: 2.5". 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.