Small Block Ford - Higher Learning

CHI Mops Up
While everyone is going cuckoo over the wild valve angles and flow numbers exhibited by GM's Gen III and IV small-blocks, their performance is just now matching what Ford accomplished with the 351 Cleveland nearly 40 years ago. Its 9.5-degree valves with a 4-degree cant were unheard of for a production motor back then, and still unheard of today. One shortcoming of the Cleveland heads, however, is that they were often better suited for high-rpm race motors than street applications. Likewise, with an extremely short production run of less than a decade, they are becoming increasingly difficult to find. And, with street motors displacing more cubes by the day, demand for them is going way up. That's where Australia-based CHI comes in, which offers a line of top-notch aftermarket Cleveland castings.

CHI offers heads with port volumes ranging from 190 to 258ccs, but its 225-cc units were the hot ticket at this year's EMC. Dubbed 3V, since its port volume falls right in between Ford's 4V and 2V heads, the CHIs offer several key improvements over the factory castings. "From a standpoint of architecture and airflow, Cleveland heads are the ultimate small-block heads from the factory, but that doesn't mean they can't be improved," explains John Konstandinou of CHI. "The biggest improvement we made is in the port sizing. Our 3V heads are like factory 4V heads but with smaller, and better-flowing ports. What a lot of people do is epoxy factory 4V heads, because the ports are way too big for street applications, so we eliminated the need to do that."

The concept of moving a large volume of air through the least amount of cross-sectional area as possible works quite well at the EMC, where low-end output is critical. CHI's 225-cc heads flow 340 cfm, despite a modest 2.4-inch cross section. "If you have a motor with small ports that flow enough air but then increase port size, you'll pick some more horsepower up top but give up a lot down low," says John. "Too often people get cylinder heads and grind on them, but very few street motors see more than 6,500 rpm, where smaller ports really help out." Other features include revised combustion chambers and hand-blended valve throats. The heads are compatible with all standard Cleveland intakes and valvetrain components, and bare castings can be found for $2,200. As good as a set of heads may look on paper, at the end of the day people want dragstrip numbers. John informs us that a 740-hp pump gas 427 with CHI heads has propelled a 3,500-pound car to 9.90s at 135 mph in the land down under. -Stephen Kim