The GrimmSpeed catless uppipe is made of 304 SS (all of it; the flanges, flex section and tubing) and has super thick, 14-gauge pipe-wall thickness, which is the most heavy-duty pipe you will find for this kind of application. Other pipes use cheaper, thinner steel and are marketed as "super light weight," not GrimmSpeed's. Also, their one-of-a-kind, Triple Layer Flex Joint is not located in the bend, which increases the life expectancy of the flex section. The inlet size is 1.92" and the pipe tapers down to 1.72", which acts as a funnel as it moves into the turbo allowing for increased air velocity. The GrimmSpeed Uppipe outlet size is a perfect match to the most common stock location turbos allowing for a smooth transition into the turbo. Because GrimmSpeed is a porting company they make sure to have the smoothest transitions possible between pipes to allow for maximum flow and quickest spool up (they call this "quality airflow"). 02-05 WRX models have a pre-turbo catalyst, making this uppipe a major performance improvement. Though the 06-07 WRX and 04-07 STI do not have a cat in the factory uppipe, this product will still improve throttle response and drivability. This product does not include the stock EGT bung.