Improves Performance. Increase the airflow into your Mustang's two valve 4.6L V8 engine to improve horsepower, torque, and overall performance with a Mustang Upper Intake Plenum.A Must For Larger Throttle Bodies. Installing a larger throttle body on the factory intake plenum still restricts incoming airflow, but now you get the most out of your Mustangs bigger throttle body by installing an upper intake plenum for improved air flow. Precision Crafted. This Intake Plenum is made from a permanent mold casting of 356 aluminum to produce a higher quality casting than conventional sand molds, which reduces porosity for an improved finish.Application. The Upper Intake Plenum is a direct bolt-in replacement for all 1996 to 2004 4.6L 2V Mustangs using a Stock, 70mm, or 75mm Throttle Body.