Big-Block Chevrolet Heads - CHP How It Works

Conventional 24-Degree Big-Block Chevy Heads are Giving Spread-Port Castings a Run for their Money

Stephen Kim Apr 1, 2011 0 Comment(s)
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Rick Roberts: Development work on our Victor 24-degree big-block Chevy heads started roughly 10 years ago. At the time, we were working with Billy Glidden on our small-block Ford heads, and he suggested integrating similar design elements into our Victor big-block Chevy heads. Cylinder heads are cylinder heads, and regardless of engine make, the same rules of airflow apply. As such, we moved the intake valve away from the cylinder wall and toward the center of the bore by 1/16 inch to assist in high-lift flow. We also moved the exhaust valve up against the cylinder bore, but in the opposite direction. A factory big-block Chevy head has 26-degree intake valves canted 4 degrees, and 17-degree exhaust valves canted 4 degrees. With the Victor heads, we changed the intake valve angle to 24 degrees with a 5.5-degree cant, and exhaust valve angle was flattened to 14 degrees. As a result, when the valves are opened 0.800 inch or more, the heads of the valves are very far away from the cylinder wall. The exhaust ports were raised as well. These changes, along with relocating the spark plug, yield more efficient combustion chambers. Changing valve angles messes up rocker arm geometry, so we had to redo the stud angles and rocker positioning. Our heads also require guideplates specific to our heads, but they’re inexpensive and readily available. Once racers started using our Victor heads, they gave us input on where they were hitting water during porting, and how we could improve the design. The result is a head that doesn’t require knocking guides out and welding up the seats, which are common practices with many conventional 24-degree castings. With 2.400 intake valves, ported Victor castings can flow 500 cfm, right on par with many spread-port heads.

Pro Stock Roots

Tony McAfee: The original port model of the spread-port big-block Chevy heads was designed by Lee Shepherd back in the mid ’80s. He was driving for Reher-Morrison’s NHRA Pro Stock program at the time, and came up with the concept of a raised-runner, spread-port head that addressed the inherent drawbacks of the factory big-block Chevy heads. Unfortunately, he died before he could do anything significant with them. The design was submitted to GM, who then sent it off to Dart for evaluation. Once the prototypes were at Dart, Richard Maskin tapped into his extensive experience in cylinder head design and manufacturing to address the problems that existed with the spread-port architecture. Since the spread-port design radically changed the configuration of the ports and the castings themselves, nothing normal would work and there were lots of valvetrain issues to fix. Lots of people had attempted to perfect the spread-port design up to that point, but Maskin is the person who really got them to work. Spread-port heads are now the standard in Pro Stock, and are used in many amateur racing classes as well.


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