Cast from prime A356 T6 aluminum, these 'Z' heads from Ford Racing were designed using solid modeling technology. They feature high - flow ports and steel alloy intake and exhaust valve seats installed (they do require a competition valve job and bowl blending). The manganese - bronze valve guides are installed with a semi - finished I.D. and the combustion chambers are CNC - machined. Laser - cut guideplates are included, and they accept both tapered seat and gasket - style 14mm spark plugs.