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: The basic premise behind a spread-port head is to significantly raise the intake ports off the deck, and spread them apart for a more efficient flow path. Combined with a smaller 18-degree valve angle, the result is a significant increase in airflow over a conventional big-block Chevy cylinder head. Back in the early ’80s, several NHRA Pro Stock teams were testing out the spread-port head design. John Callies was the director of motorsports for Pontiac at the time, and he was able to get a head casting legalized for Pro Stock competition. The heads were for big-block Chevy engines, not Pontiacs, but they had a Pontiac part number and logo since they were intended for use in Pontiac-bodied race cars. GM submitted the heads to Richard (Dick) Maskin for his help in sorting out the design. From there, several manufacturers started offering their own spread-port castings, and most these days feature an 11-14 degree valve angle. Edelbrock was one of the last companies to join the spread-port party, but this enabled us to address many of the valvetrain geometry issues associated with this style of cylinder head. We have just about the best 18-degree head you can hope to have. Cylinder heads are almost like women’s fashion, and small valve angles are fashionable these days. It’s not that 18 degrees aren’t capable, they’re just out of fashion.

Conventional vs. Spread-Port Heads

Jason Neugent: Several factors distinguish a spread-portstyle cylinder head from a conventional big-block Chevy casting. Spread-portstyle Big Duke cylinder heads are much taller than your conventional 24-degree big-block Chevy castings. The primary benefit of a spread-port design is that it provides a straighter direction for the air to flow. Likewise, it also allows for equal volume and airflow from port to port, whereas a conventional-style head will have long and short ports. The result is different port volumes and airflow from one intake port to the next. That’s why people often refer to good ports and bad ports when describing big-block Chevy heads. Airflow potential for a max effort Big Duke head is tremendous. We have a new CNC-ported 12-degree Big Duke head that will flow 578 cfm at 0.900-inch lift. Brodix offers spread-port heads in a variety of options, which results in a big range of prices. The Big Duke sets start at a retail price of $3,750, topping out at $8,800. Big Dukes also require special pistons, big-bore blocks, shaft-mount rocker arms, longer valves and specific gaskets, valve covers, and intake manifolds.


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