3 diameter into 2.25 reverse Y - pipe. Adding this Mid - Pipe with Y - Pipe to an Axle - Back system will give you all the elements of a Cat - Back system. These Mid - Pipes are NOT intended for use with OE factory mufflers. Built from premium T - 304 stainless steel, superior to T - 400 series (such as 409), to give you the absolute best in performance and durability. Ultra - smooth mandrel bends ensure maximum flow power, and precision computer numerical control (CNC) manufacturing ensures an accurate fit. Best of all, BORLA stands behind every Mid - Pipe with a Y - Pipe with a Million - Mile Warranty. Just what you'd expect from the world's most experienced (and most winning) exhaust brand.