Chevy Big Block Crate 454 Engine - Import Killer, Part 2

The AFR head swap was simple, with the only major change being the need for two extra-long head bolts per side [inset] to fasten the outside row of bolts along the exhaust ports. These longer head bolts are required on many aftermarket big-block heads, and are available from AFR when you order the heads. Unlike earlier GM Gen V big-blocks, the 454 H.O.'s Gen VI block accepts all Mark IV, Gen V, and Gen VI cylinder heads without interchange issues.

For all the testing with the factory iron heads, we used the stock, nonadjustable stamped-steel 1.7:1 rocker arms. The AFR heads are set up for a conventional stud-mounted adjustable valvetrain, so we enlisted a set of Crane's Widebody Gold series aluminum rocker arms. With this combination, we were able to reuse the same stock-length pushrods with the hydraulic roller camshaft. When we swapped in the Crane solid-roller cam, we needed to substitute 0.100-inch longer pushrods to maintain proper rocker-arm geometry.

AFR's Tony Mamo, the chief designer of the company's line of big-block Chevy heads, brought a few sets of AFR intake manifold gaskets with him. We tested the AFR 305 heads with two intakes: an Edelbrock Performer RPM dual-plane, and a Victor Jr. single-plane (see Dyno Results chart). As expected, the single-plane gained high-rpm power but sacrificed low-end grunt.