Chevy double-hump heads are stock cylinder heads that are very popular for use in Street Stock and Pure Stock racing classes because they can be race ready with minimal modifications. These heads feature small chambers for high octane fuel, smaller intake ports and larger valves for better flow. The ports, while small for a big street motor, are perfect for racing classes that require a 500 CFM two barrel carburetor..
Chevy's double-hump heads got their nickname because of the raised identification shape on each end. It has two half ovals connected by a straight bar, hence why it's described as "two humps". Some variations are also nicknamed "Fuelie" heads because a version appeared on the fuel injected 327 powered Corvette. In addition, not all double-hump heads perform equally. Chevy made small variations to the design over the course of its production, each branding a different part number. Although some models come with a smaller valve, they can easily be modified to the larger valve size by cutting the larger seats on the smaller valve, and opening up the heads' bowl area by a valve seat and guide machine. This operation should be well within the rules that most race classes require.