1974 NASCAR International Stock Car Racing Rule Book Modified Division Section 20C-20 -- Safety Spoilers

a. An approved spoiler must be a solid non-adjustable part of the body which controls the flow of air over one surface only. In the interest of safety and handling characteristics, a non-adjustable spoiler not exceeding 7 inches in height may be attached to rear deck lid. An approved spoiler may be mounted to the front underside of cars. The optional non-adjustable front spoiler must be installed a minimum of 3" behind the lower trailing edge of the front bumper and the leading edge of the spoiler cannot extend forward beyond the lower trailing edge of the bumper and cannot extend over 2" below the lowest point of frontal area. Spoiler cannot extend beyond center line of front frame rails. Spoilers must have a minimum ground clearance of 2". All support brackets must be mounted to rear of spoiler -- only NASCAR approved spoilers permitted.