Chevrolet Performance cast iron Vortec cylinder heads will fit 1958 and later small block Chevy engines, and offer a 20 to 40 hp increase over earlier cast iron small block heads. Features include fast burn combustion chambers, and a high-velocity port design. They require the use of a Vortec-style intake and self-aligning rocker arms, and come complete with valves, springs, and retainers. Cast Iron L31 Vortec Small Block Chevrolet Assembled Cylinder Head
