Specially designed Lid,Filter, and Base. These help reduce Venturi effect across the carburetor to give more consistent air into the butterfly. Less trouble jetting. Smoother acceleration off the center of corner. Straighter, Cleaner air to the carburetor. No stumble due to air pressure differentials. The lid and base have a female cavity that help align the filter with the male cavity to help gasket between them. Any wedge nose cars like Modifieds and Late Models need to reduce the air coming across the top of the carburetor at yaw. This is the solution.