You find a TGV assembly on most modern Subaru models. TGV stands for Tumble Generator Valve, referring to a flapper valve in the TGV assembly that is designed to create a “tumble” effect to the air entering your engine. That valve is only there for cold start emission standards, which is why TGV valves were not used by Subaru in other countries, such as Japan. For even when the valve is fully open it blocks a good percentage of overall air flow. On a totally stock car it has little impact, but when you upgrade to bigger turbochargers, intercoolers, or exhaust systems they all need greater air flow. The design of the standard TGV assembly can also make it difficult to install some larger turbochargers to your Subaru. It can cause a TGV error code to come up, but that is easily removed with all ECU tuning solutions. There is two different types of TGV Deletes for Subaru models, side-feed or top-feed injected. So make sure you order the right part! We consider this an essential part when building your big-power engine! The AVOTurboworld prepared TGV's do not have the valves in the unit plus are powdercoated in STI red wrinkle.