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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Tony Mamo: The greatest weakness in the factory big-block Chevy cylinder head architecture is that there are two pairs of completely different intake ports in each head. Both the port length and the flow are notably different in both of these pairs as well as the architecture and overall layout of the port. The combustion chamber design of the original OEM heads leaves a lot to be desired as well, especially their closed chamber design, which really hampers flow and performance. Its greatest strength is the fact that it’s a large head with a lot of room to work on improving some of its inefficiencies when it comes to its port and chamber design. Also, with the ability to raise the height of the exhaust port in an aftermarket casting, another large shortcoming of the OEM design is greatly improved upon.

The latest crop of large, efficient 24-degree heads like our 385cc castings are certainly encroaching on the airflow and power capabilities of some of the over-the-counter, spread-port heads from 5 to 10 years ago despite the fact that the spread-port design has a huge advantage with a raised intake runner and a much better port layout. How did it happen? Like it always does in this industry: By constantly pushing the envelope on the R&D side of things, and, of course, a lot of sheer determination to produce a better product. The 24-degree conventional head market is still a really hot market, and the time invested in producing a new higher flowing product is very much warranted. Truthfully, it’s hard to believe some of the flow we are getting these days out of conventional, nonraised-runner port designs, and had you asked me just five years ago, I may have said it was impossible to get where we are today.

Tony McAfee: Achieving big airflow, while working around the limitations of the factory big-block Chevy cylinder head architecture, is very challenging. In order to keep costs down with a standard 26-/24-degree head, it must be compatible with the stock valvetrain. Consequently, the trick is to manipulate the port design and cross-section around the stock valve location. While high-end conventional big-block Chevy heads do have raised exhaust ports, the intake ports remain in the stock location. To work around this limitation, the short-turn radius on the intake port is raised tremendously and the plugs are relocated as well. Competition amongst manufacturers has pushed things to the next level, and racers are the beneficiaries. The result is conventional head castings with outstanding airflow that are compatible with off-the-shelf components.


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