Each holley power valve is stamped with a number to indicate its vacuum opening point.. For example, the number 65 indicates that the valve will open when engine vacuum drops to 6.5 in.
The holley brand is synonymous with automotive performance.. Ever since then, holley has been one of the preeminent names in fuel delivery and carburetion, both as oem for automakers and as an aftermarket upgrade for enthusiasts, weekend racers, performance.