Cylinder Head Database

Small-block Chevy cylinder heads can be categorized in several different ways. One of the easiest is to group them by intake-port volume. For the purposes of this story, we will organize these heads into three categories: Category 1, 179 cc and smaller; Category 2, 180 cc to 199 cc; and Category 3, 200 cc to 220 cc. Unmolested production heads generally fall in Category 1, but not always. For this test, we've evaluated most of the popular heads. For the earlier heads, we'll refer to them by the last three digits of their casting number, as in 462 heads, which were early castings that had a 64cc combustion-chamber volume and were used on 327 and 302 engines. The later heads will be referred to by their application, such as the aluminum L98 TPI castings, the LT1 and LT4 5.7L engines, as well as the cast-iron Vortec head and the new LS1.

While we have separated these heads by port volume, greater size doesn't guarantee increased airflow. The advantage to midsize heads is that they combine increased airflow without sacrificing velocity, which tends to promote strong torque. One way to look at cylinder-head flow is to include velocity when evaluating heads. In other words, an intake port the size of a tennis ball will probably flow tons of air but at a snail-like velocity. Conversely, smaller port volumes will suffer from flow restrictions but offer fantastic velocity. Velocity, then, can be equated with good torque and excellent throttle response.

If there is a magical combination, it would have to be a port with great airflow and outstanding velocity. This is especially true for intake ports. A good example of an extra-large intake port that didn't work would be the '69-'70 Ford Boss 302 engine. The ports on that engine are huge. Those engines made decent horsepower but were infamous for their lack of torque. This is also due to cam timing but mainly to the expansive intake ports. That's why pure airflow numbers can be misleading. You must also consider the application for which the cylinder will be used. For example, it would be folly to bolt a huge 220cc intake port head on a daily-driven 283ci street car.