The TurboXS WRX & STI uppipe is manufactured to exacting standards. Removing the restrictive factory catalytic converter uppipe, you will increase exhaust flow to the turbocharger, increased HP, reduced turbo lag, and eliminate the chances of a damaged catalytic converter destroying your turbocharger. The TurboXS uppipe offers a flex section to help with fitment and a stainless steel finish to improve durability. The TurboXS uppipe has an inner diameter of 45mm; this is the exact same size as a stock Subaru turbocharger inlet. This promotes the best possible performance throughout the entire RPM range by maintaining exhaust velocity. Oversizing the inner diameter of the uppipe slows exhaust velocity and creates turbulence as it enters the smaller inlet of the turbocharger, potentially even hurting turbocharger spool up. 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.