6014 - S350 - 29cc ARC Billet Cylinder Heads for the Briggs Flathead is made from 6061 T-6 Aluminum. These heads were designed for maximum heat retention, which is a desirable trait for Junior Dragsters. The "S" pre-fix denotes the depth of the combustion chamber. (S350 = 0.350") These heads have a valve diameter of 1.25" for the intake and 1.125" for the exhaust.