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: Conventional big-block Chevy heads can come close to spread-port castings airflow-wise, but spread-port heads still have a power advantage. Due to their smaller combustion chambers, in a high-compression application you’ll have a smaller piston dome on a spread-port motor than with conventional heads. A smaller, more gradual dome slope promotes more efficient combustion. Likewise, even if the peak airflow numbers between the two styles of heads are similar, a spread-port head will have superior mid- and low-lift flow than a conventional head. Spread-port heads also lend to more efficient intake manifolds as well, especially if you’re limited to a single carb. If you’re not bound by rules or restrictions, when comparing an optimized spread-port engine combo to an optimized conventional-headed combo, a spread-port head is simply the better way to go. If you’re starting from scratch, why mess around with conventional head and leave horsepower on the table? Comparing like-for-like engine combos with the same durability, you’ll make 100 more horsepower with a spread-port head and you’re not going to have to work it as hard to make that power.

Tony Mamo: A spread-port head design offers similar-flowing ports in every hole, whereas a 24-degree design will always be handicapped by four ports flowing weaker than the other four. Even a good 24-degree head will still usually fall short on the bad ports by about 20 cfm. In fact, I have seen as much as a 50 cfm disparity in the weaker 24-degree designs. Then there is the more consistent cross-sectional area of the spread-port design with less velocity deviation, and also the fact the intake manifold design and layout has a much straighter shot at the back of the valve and ultimately the combustion chamber so it allows for more airflow net to be converted into power. Conversely, 24-degree heads don’t have as sweet a vantage point when it comes to manifold design, but due to the fact that the intakes are typically much shorter, they do fit a lot better in cramped engine bays and other applications where the sheer height of the spread-portstyle motor simply couldn’t be tolerated. Flatter valve angles common to the spread-port design will also have better burn characteristics and take less timing advance to make peak power. Truthfully, it’s a lot of little things that add up to create a situation where the spread-port is a more efficient design. Ultimately, if you’re looking for the most power you can generate with the displacement and compression you’re working with, and you’re willing to spend the money necessary to get there, the spread-port heads won’t disappoint. However, the difference now in 2011 is a well-prepped combo with 24-degree heads might be on your back bumper in the other lane, or worse if he really did his homework. Even just five years ago that simply wasn’t possible! CHP


Air Flow Research
Valencia, CA 91355
Trick Flow Specialties
Tallmadge, OH 44278
Mena, AR 71953
Dart Heads
Troy, MI 48084


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