As an example, if the cylinder head flows 275 cfm @ 28 inches of water, and with the intake manifold and carburetor it only flows 206 cfm, a 25 percent flow loss is present.

Each head is carefully placed on the SuperFlow 600 flow bench and tested from 0.050-inch to 0.0700-inch valve lift. In most cases, the heads were tested twice to ensure the accuracy of the flow ...

Note that the difference between the boiler feed pump head-flow curve and the system resistance curve (Figure 1) provides the basis for the pressure drop available for the drum level control valve.