Proheader PM120S - SBC Small Block Chevy Straight Plug Aluminum Cylinder Heads 64cc Small Block Straight Plug Aluminum Cylinder Heads, 64cc Chamber, 198cc Runner, 2.020 Intake/1.600 Exhaust Valve with Fully Machined Surfaces, Set of 2 are proud to introduce first aluminum alloy SBC cylinder heads. The process that heads are constructed is through a permanent mold casting. This casting process involves pouring the molten alloy by gravity into a steel mold. These SBC heads have a 198cc Runner with 64cc combustion chambers with heart shaped chambers. These heads feature a straight plug design. The valve guides are bronze and the valve seats are all hardened and will except up to a 2.050 intake valve (with machining). Inside the pocket of the intake has a ridge that produces a better swirl of air flow and a 1.600 exhaust valve with a smooth pocket to exit the gas quickly. The exhaust and intake surfaces are flat and have been fully machined and will except a both Vortech style and a conventional style SBC intake. The exhaust bolt patterns raised .100 thousand. head also features a deck thickness of .625?. Spring seats are cut to 1.550? diameter to allow almost any spring combination. rocker stud holes feature heli coils to prevent rocker stud to be pull though.