1975 NASCAR International Stock Car Racing Rule Book NASCAR Grand National ® Championship Division Section 20-5 -- Air Cleaner and Air Intake

a. Only NASCAR approved round air cleaner minimum 12 inches -- maximum 20 inches diameter will be permitted. A NASCAR approved complete dry type element -- minimum 1 1/2 inches -- maximum 5 inches high, must be used in the air cleaner at all times. All air shall be filtered through element. Top of air cleaner must be solid -- no holes. No heat shields permitted. Air cleaners cannot be removed.

b. Cowls

(1) No cowl air induction permitted.

(2) All cowl openings, previously used, must be completely closed off. Absolutely no ducts or baffles permitted on or leading to the air cleaner or element.

(3) The front of cowl must seal to the back of the hood when the hood closes. This will be done by putting flat sheet metal on the front of the cowl with weather stripping across the top of the sheet metal. The center of the sheet metal may be altered as follows only: A rectangular opening, maximum 20 inches long by 2 1/2 inches wide may be removed from the sheet metal at the center of the cowl. The 2 1/2 inches shall be measured at the point that the hood seals to the cowl. Slanted or angle cowls not permitted. Roll bar padding not permitted for sealing.