Compared to the 392 Apache head, the Hellcat head looks very similar, but the Hellcat heads are cast at a specialty low volume using Hellcat specific tooling. The Apache head is a 319 alloy while the Hellcat head is a premium heat-treated 356-T6 alloy, giving it higher thermal conductivity and improved elongation (one of the measures of an alloy's strength). Of note are the differences in the valves. The Modern Muscle valves are a custom proprietary valve with a thicker cross section for higher horsepower applications.