Bridging the "Conventional" Gap
"Cylinder head and port design is moving forward at a blinding pace, and heads are becoming more specialized. Customers want more power for less money, and this is what spurs on the development of higher-flowing and more efficient heads. The conventional 24-degree big-block Chevy category of cylinder heads has become blurred and will continue to get hazier as time goes on. Some of these 24-degree conventional BBC heads are now flowing as much as some spread-port heads! For example, I designed a 24-degree head for a class called Texas Pro Stock. Its rules call for 24-degree conventional BBC heads rolled to no less than 22 degrees, and allow for a cast single-plane intake manifold and dry-sump oiling. Most of these engines are 565 ci and the last set of heads I did-called the Profiler Performance Sniper X 24-degree heads-had 2.375-inch intake valves and flowed 385 cfm at 0.500-inch and 520 cfm at 0.900. That's way more than I thought was possible just 10 years ago. That engine produced 1,230 hp at 8,400 rpm, and propelled a 2,300-pound car down the eighth-mile in 4.52 seconds. Think about that for moment and let it sink in.
"Now let's look at the pros and cons of a set of spread-port heads versus a set of 24-degree conventional BBC heads with the exact same airflow curve. Just because the heads flow the same doesn't mean they will make the same power. The induction flow path of the 24- or 22-degree conventional BBC heads is less than desirable and the combustion chambers aren't as efficient. The spread-port heads have a straight port and a better induction system flow path aimed right up at the carburetor venturi. They also have very efficient combustion chambers. Even though they have the same flow, the spread-port heads can produce another 100-125 hp."
Kevin feeney: "Conventional heads with standard valve angles and port heights have come a long way in recent years. For instance, with today's 23-degree small-block Chevy heads, you can produce comparable power to 18-degree heads at a far lower cost since they don't require the expensive custom pistons, valvetrain hardware, and intake manifold. The downside is that these heads don't lend themselves to as small of a combustion chamber as with 18-degree style heads, requiring a tall-dome piston in a high-compression engine, which results in the need for more timing and a heavier piston. With that being said, RHS has helped bridge this gap with a few small-chamber 23-degree-style head options where the valve angle has been rolled slightly. This results in a smaller chamber while still utilizing off-the-shelf 23-degree components."