3" is the way to go when talking downpipes. The Mishimoto 2014-2017 Fiesta ST downpipe is 3" from the turbine outlet flange all the way to the 2-bolt exhaust flange. Maximizing flow and reducing backpressure is the key to unlocking power in any turbocharged vehicle. The reduced backpressure speeds up turbo spool to drop the boost threshold lower in the rev range. To boost the size of your entire exhaust system, pick up the Mishimoto 2014-2017 Fiesta ST Cat-Back Exhaust for most impressive results. 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 2014-2017 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 2014-2017 Fiesta ST downpipe bolts effortlessly to the stock system or any aftermarket exhaust with a 2.5" mid-pipe!