These cylinder heads feature an extra thick deck and extra material in the spring pockets for a heavy-duty casting that can be used with high-lift cam and heavy spring combinations. Edelbrock equips the complete heads with your choice of spring packages to suit hydraulic or mechanical roller cams. Choose a hydraulic spring package for flat tappet or hydraulic roller cams up to . 700 lift. Mechanical roller cam spec include Manley dual-spring valve springs and titanium retainers good for up to . 880 lift. The 300cc rectangle ports produce impressive flow and great power on competition big-blocks up to 510 c. i. d. with 4. 310 or larger bore. Exhaust port exits are raised . 534 to greatly improve exhaust flow and power.