The Edelbrock 615469 Big Block Chevy DR-17 Pro-Port Cylinder head is designed specifically for the professional cylinder head porter and engine builder. Like the other Edelbrock Cylinder head, The Pro-Port cylinder head is also cast in the USA at the state-of-the-art Edelbrock Foundry with extra-thick walls to allow for custom CNC porting. In most cases, seats and manganese-bronze valve guides are included, but not installed. Please note: This head can not be used without professional head preparation. Pro-Port RAW Features Include: - Unported versions of Edelbrock race-winning Victor Series CNC head for the professional cylinder head porter and engine builder - The Pro-Port cylinder head is cast in the USA at the state-of-the-art Edelbrock Foundry with extra-thick walls to allow for custom CNC porting - The only head designed specifically to accommodate almost any CNC port shape, size or location - Offers enough wall thickness for CNC machining to various port dimensions - In most cases seats and manganese-bronze valve guides are included - Some of the Edelbrock Pro-Port Raw Head Feature Our Special Hot Isostatic Pressing or HIP Process.