Chevy BBC 454 320cc 119cc Hydraulic Flat Assembled Cylinder Heads

Assembly Specifications Max Lift: .550 Coil Bind: .740 Intake Install: 130lbs @ 1.8 Exhaust Install: 130lbs @ 1.8 Closed Sear Pressure: 110lbs Open Seat Pressure: 300lbs As with all Speedmaster cylinder heads, our Big Block Chevrolet heads are Gravity Die Cast . This casting process creates a much more uniform and robust cylinder head. With the increasingly large displacements becoming common, the need for more airflow is necessary. If you are looking to build a 400-500+hp engine, give our PCE281.1489 heads a try. They offer a smaller cross - section to increase the incoming air s velocity, resulting in great driveability, power and economy. On engines over 500hp, use the rectangle port PCE281.1488 heads. The mid-size cross section works well on engines under 540cu.in and under 7000RPM. If you are working on a larger, or higher RPM engine, step up to the CNC ported PCE281.1511 heads. The added volume of the PCE281.