Related Photo Galleries
When the dust settled, the new iron head from GM Performance Parts outperformed the stock--though admittedly smaller-volume--aluminum cylinder heads of the ZZ4, as well as the aluminum Fast Burn head. With the small-port Vortec Bow-Tie, the Hot cam, 1.6 rockers, a single-plane intake, and a 2-inch spacer, the ZZ4 generated a best average of 391 hp. A similarly configured setup with the large-port heads made 386 hp, on average. Both figures are a staggering jump over the stock ZZ4's 328.5hp average.