68 383 with 750 carb. Runs rich

The power valve is simply an on/off switch. The # determines at what vacuum level that "switch" opens. (i.e.: 6.5") The amount of fuel flow is determined by the size of the 2 little holes under the power valve - PVCR (power valve channel restrictions)

There are several theories as to what power valve will suit your needs and variables in the vehicle. Needs/applications vary. So the power valve opening formula may be different for a drag car as compared to a street car. In some cases, the power valve is removed and jetting sized raised to compensate. The bigger the PVCR, the larger the jet size is needed to compensate when the power valve is removed & blocked off.