[gumby79]

In Oregon wipers required glass to wipe optional.
For it to work some ducting would be needed or the interior voids would destroy any posability of smooth flow. At the dirt track closing off the interior was reserved for the uper street class , as a performance advantage .Problem the front hole is normally biger than the rear hole + driver blockage. Desine it as a converging diverging duct system.
Most cars would see better results from a trip to the guillotine to remove everything from the window sill up(windshield less convertible).