Identifying Double Hump Chevy heads can be tricky, especially for those new to engine work. These iconic cylinder heads, known for their distinctive "double hump" design on the intake ports, were used on small-block Chevrolet V8 engines from the late 1950s through the early 1970s. This guide will equip you with the knowledge to accurately identify these heads, covering key features and common variations.
Understanding the "Double Hump" Design
The name "double hump" comes from the shape of the intake ports. Unlike the more rounded ports found on later heads, these ports feature two distinct peaks or humps, contributing to their unique flow characteristics. This design, while visually striking, is only one piece of the identification puzzle.
Key Identification Features: More Than Just the Humps
While the double hump is a strong indicator, other features are crucial for definitive identification. Don't rely solely on visual inspection of the ports; several other markings and characteristics will help you confirm the head's identity:
1. Casting Numbers: The Definitive Identifier
The most reliable way to identify Double Hump Chevy heads is by checking the casting number. This number is usually stamped on the head's side, often near the spark plug holes or the valve cover rail. Different casting numbers correspond to different variations of the head, indicating features like chamber volume, bolt patterns, and valve sizes. You can find comprehensive lists of casting numbers and their corresponding specifications online through various automotive enthusiast forums and resources dedicated to classic Chevy engines.
2. Bolt Patterns: Matching the Block
The bolt pattern on the head's mating surface must align precisely with the engine block. Double hump heads have specific bolt patterns that differentiate them from other generations of small-block Chevy heads. Incorrect bolt patterns will prevent the heads from fitting properly, potentially causing significant engine damage.
3. Valve Sizes: A Subtle Clue
While not always consistent across all casting numbers, the valve sizes can provide additional clues. Measuring the valve diameter can help narrow down the possibilities. However, remember that valve sizes can be altered through modifications, so this should be used as supporting evidence, not the primary identifier.
4. Combustion Chamber Shape and Volume: For the Experienced Eye
The combustion chamber shape itself, beyond the intake port, exhibits characteristics specific to the double hump design. Experienced engine builders can often identify heads based on subtle differences in chamber shape and volume. However, this requires a keen eye and significant experience, making casting numbers the preferred identification method.
Common Variations and Their Significance
Several variations of Double Hump heads exist, each with slightly different characteristics that affect performance and compatibility. These variations are primarily defined by their casting numbers. Researching the specific casting number found on your heads will reveal important details about their design and capabilities.
Tools and Resources for Identification
Accurate identification requires careful examination and access to reliable resources. Here are some tools and resources that can assist in the process:
- Caliper: For measuring valve sizes.
- Casting Number Cross-Reference Charts: These are readily available online through numerous sources, providing details on specific casting numbers.
- Automotive Forums and Communities: Connecting with other classic Chevy enthusiasts can provide valuable insights and assistance in identification.
Conclusion: Accurate Identification is Crucial
Correctly identifying Double Hump Chevy heads is critical for engine rebuilding and performance modifications. By understanding the key identification features and utilizing available resources, you can ensure compatibility and avoid potential problems. Remember that using the casting number is the most reliable way to identify these heads precisely. Don’t rely on visual inspection alone; always cross-reference the casting number with available databases for confirmation.
