The Edelbrock E-Street Cylinder Heads for GM LS Cathedral Port 64cc Pair #77617 are designed for any high performance or stock replacement application and offers the best performance values for aftermarket GM LS Cathedral port heads. These bare cylinder heads are engineered with the same architecture as the factory head, and all stock components will fit without issue. Edelbrock E-Street LS Cathedral Port Cylinder Heads are manufactured with premium material and machined to the industry's tightest tolerances. They feature premium manganese bronze valve guides for long wear with particular emphasis placed on holding precision tolerances on valve seat concentricity. This allows the valves to seal securely to eliminate any leak down and increase cylinder pressures during engine operation. All Edelbrock cylinder heads feature patented Clean Cast Technology(TM) , a revolutionary process that eliminates casting flaws and promotes a smoother internal surface finish for greater air and coolant flow. These benefits provide more power and increased cooling ability right out of the box. A unique dual spark plug pocket design allows you to use both the factory style tapered seat spark plug or gasketed seat spark plugs that are available in wider heat ranges for maximum tunability.