The Invidia downpipe is 3" in diameter which is larger than stock and helps relieve back pressure from the exhaust system. This will help you achieve higher power levels and help the turbo spooling and flow characteristics in your FA20DIT powered Subaru WRX. This is a great addition to anyone seeking a simple increase in power or can be a great supporting modification to make more power from future performance parts as well. Full stainless steel construction is executed for strength and durability. Fitment is just like factory and will connect to the factory catback using any of the available adapters for stock catback to 3" downpipe.