The -11X is the best flowing 23° head out of the box that BRODIX offers. BRODIX recommends this head be installed on a 400 cu in or larger engine. The -11X requires a special stud girdle and longer pushrods. Piston valve notches must be checked for clearance. a valve length of . 150 longer than stock is required. The BRODIX deck surface is the strongest in the industry allowing use of nitrous and blowers. Hardened valve seats are standard allowing use with unleaded fuels. Phosphorous bronze valve guides assure proper valve guide wear. When thinking of small block Chevy heads - think BRODIX. The -11X may not have the spring pockets cut any larger or deeper than 1. 550.