An automobile diffuser is the upwardly-ramped surface at the rear of the vehicle's underbody. Aerodynamic downforce and drag are generated as airflow travels underneath and along the ramped surface of the diffuser. However, with a moderate drag penalty, the downforce-producing effect of the diffuser can be further enhanced by an arrangement of aerodynamic devices along the ramp surface and within the diverging flow channel of the vehicle's diffuser.