Vortex generators are mounted on the roof of cars. They are designed to break up the airflow and reduce aerodynamic stalling. Many high performance models such as the Evo and the Impreza are being fitted with these. We are seeing a growing range of aftermarket carbon fibre and carbon fibre look vortex generators fitted to cars. The merits of an aerodynamic modification like this is questionable on a road car but in a competitive track environment every little bit helps.