The rear diffuser for our Trans Am was designed exclusively for the ’93-02 Trans Am, as the factory bumper cover to our Pontiac is exclusive for the T/A — base Firebirds and Firebird Formulas used a different bumper cover, so this particular piece won’t work for those vehicles. Rear diffusers are intended to improve the car’s aerodynamic properties by enhancing the transition between the high-velocity airflow underneath the car and the much slower “freestream” airflow of the ambient atmosphere.