Monster-cubic-inch stroker Big-Blocks need lots of air to maximize theirperformance potential and Chevrolet Performance Bowtie race cylinder headsare designed for that task. They are made of 356-T6 aluminum with huge,raised intake ports, larger valves, smaller combustion chambers and twoadditional head bolts for increased clamping force. The runners are purposelyleft smaller, so there is ample room for custom porting by the engine builder.