Chevrolet double hump, or camel hump, cylinder heads are named after the casting mark found on the front of each cylinder head. These heads are highly sought by restorers and engine builders for their high performance capabilities, due to large intake ports. There are two types of double hump heads -- large hump and small hump -- differentiating early and later versions. These heads were used from 1968 to 1970, and they were nicknamed the "fuelie." You can identify double hump heads by locating the casting number and the casting mark.
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Identify the casting mark. According to the Fastnuf website, the casting marks are found at the front of each cylinder head, facing towards the radiator. The mark is a rectangle with two humps, one at each end of the rectangle. On small hump heads, the rectangle is significantly smaller. An illustration of both casting marks is found on the Fastnuf website (see References). An image showing the large hump casting mark is found on the Circle Track website (see Resources).
Remove one of the valve covers to locate the casting number. The seven-digit casting number is located centrally on the top of the cylinder head, between two valves. An image of the casting number location is found on the One Dirt website (see References).
Decode the casting number. Fastnuf identifies double hump heads by the last three digits of the seven-digit casting number. The older large hump heads, manufactured in 1968, end with the numbers 291, 461, 461X and 462. The small hump heads, manufactured in 1969 and 1970, end with the numbers 186 and 492. Fastnuf also identifies each number further, giving engine specifics.
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