[speed220mph]

Michael: Positive crankcase valves are calibrated for specific engines. The PCV system on an engine is a controlled vaccum leak as are carburetior or FI throttle plates. The bigger the engine, the more air--crankcase vapor--must be evacuated by the PCV valve. Therefore, PCV valves are calibrated to the requirements of the engine. However, if you choose a valve which was used on a larger engine such as 6--8 liters, one valve will work.

The thing you hear when shaking a PCV assembly back and forth is a spring-loaded shuttle valve. This valve is forced against a spring by manifold vacuum and crankcase pressure. Thus, it maximum flow restriction at idle and wide-open throttle to limit air/fuel mixture leaning. The spring pushes the valve open to provide maximum flow during part-throttle operation. So, if your engine is jetted toward the lean side, the addition of a PCV system will require slightly fatter jets.