The Mishimoto Fiesta ST downpipe is 3" diameter from the turbine outlet flange all the way to the flex pipe. Maximizing flow and reducing backpressure is the key to unlocking potential in any turbocharged vehicle. The reduced backpressure speeds up turbo spool to drop the boost threshold lower in the rev range. Full 304 stainless steel construction prevents corrosion and eventual failure that plagues aluminized steel systems. The 3" turbine to downpipe flange is CNC-machined for a leak-free connection and easy installation. Next in line on this Fiesta ST downpipe is the high-flow catalytic converter, which frees up some airflow when compared to the beefy stock equipment. Just in case you wanted to keep your stock cat-back system, this Fiesta ST downpipe bolts effortlessly to the stock system or any aftermarket exhaust with a 2-1/2" mid-pipe!