The Victor CNC DR-17 Oval-Port Cylinder Heads for Big-Block Chevrolet engines (PN 615467) have a larger 120cc combustion chamber designed for large displacement, high-horsepower, naturally aspirated engines running on pump gas. This design allows for a true flat-top piston configuration, promoting greater efficiency and power output. Offered "bare," these heads feature a 425cc port volume, 2.450" intake valves, 1.850" exhaust valves, raised intake and exhaust ports, and a relocated spark plug position. The raised intake and exhaust ports are particularly beneficial in maximizing cylinder fill during the valve opening cycle, while the revised spark plug location ensures a more complete combustion. Combined with optimized valve placement, these improvements result in better airflow, more power, and higher overall engine efficiency.Each Victor CNC DR-17 cylinder head is cast at Edelbrock's state-of-the-art foundry using premium aluminum alloy and machined in the Edelbrock Race Center in Mooresville, North Carolina. This material undergoes hot isostatic pressing (H.I.P.) to ensure a more stable and dense grain structure, which increases durability and performance. The heads feature large CNC oval ports explicitly designed to maintain high airspeed, contributing to a high torque curve throughout the engine's operating range.Manufactured to the industry's tightest tolerances, these heads come fully CNC-machined, including their ports and combustion chambers. A 17° valve angle is incorporated to improve flow capability, while ductile-iron interlocking valve seats and premium manganese-bronze valve guides ensure long-lasting performance. The valve seat concentricity precision allows a perfect seal, eliminating leak-down and increasing cylinder pressure during operation. These heads are designed to be used with a shaft rocker system and can bolt directly onto standard deck blocks with a tall-deck manifold, but tall deck blocks require intake runner spacers.