For Subaru WRX/STI Catback Exhaust System 3.5" Tip Muffler - GD GG Made of high quality T-304 stainless steel. TIG welded CNC machine flange for resistance against pressure and corrosion. Aggressive deep and smooth tone sound while ensures smooth exhaust gas flow. Increase engine output and efficiency. Dyno proven to instantly increases 15 to 25 horsepower or low end torque