With the new horsepower adjustment for Stock and Super Stock that became effective June 16, the NHRA technical department has officially accepted the Edelbrock 390 cylinder head (part number 60057) and the Edelbrock 428 cylinder head (60058) for use in Stock and Super Stock competition.

Much speculation has swirled around the development and adjustments placed on the combinations that utilize these cylinder heads. The initial plans for the heads were to place a 15-horsepower increase in Stock and 10-horsepower addition in Super Stock above the factored horsepower. After further analysis, the numbers were reduced. Effective with this announcement, an eight-horsepower increase has been added to Stock combinations and five-horsepower increase to Super Stock. The only application not eligible for the use of the Edelbrock cylinder heads is the Shelby 428.

In the initial stages of acceptance, the Edelbrock heads were eligible for use in applications where the F5 (Stock) and the Canadian (Super Stock) versions were used. After further review, the Edelbrock cylinder heads are accepted replacements for use on all 390 and 428 Ford applications from 1961 to 1970.

These adjustments are reflected in the current Stock and Super Stock classification guides that are available here.