There was a discussion about late '60's Camaros and their spoiler options in Stock and Super Stock racing. Apparently the spoiler option included the front & rear together. Some were trying to run with only the front spoiler, which wasn't legal. The front spoiler was said to help aerodynamics by keeping some of the air from getting underneath while the rear ducktail spoiler was left off because it caused more drag and slowed the car a bit in a drag racing application.
Absolute fact. Remove the rear spoiler on a Camaro and mph goes up. Front spoiler blocks air from getting under the car and mph goes up. There are also small panels that block air from bypassing the radiator used only on a/c Camaros that also improve mph. I would even go so far as blocking off the back side of the grille completely with clear Plexiglas on a drag race only car and get even better airflow over the car and increase pressure in the area of the cowl induction inlet if I thought it would slip by the inspectors.
