This high flow PCV valve functions better with the lower vacuum signal of a performance engine using a camshaft with more duration and overlap. 

PCV valves are not all calibrated the same, and perform differently depending upon the amount of vacuum an engine produces.  A performance camshaft will typically produce a lower vacuum signal than the stock engine/camshaft, and the stock PCV valve may not close enough at idle, which can cause an irregular and/or high idle, or otherwise not function efficiently throughout the operating range of the engine.  An improperly functioning PCV valve can also cause the premature break-down of engine oil, sludge build-up, leaking gaskets and seals, water vapor build-up, as well as allow excessive oil to enter the intake manifold.  A PCV valve that closes too easily and completely, can stay closed too long above idle, and can also interfere with the proper evacuation of blow-by gases.  This PCV valve functions better at a lower vacuum signal, but still opens once the engine vacuum changes during all-around operation.

Grommet end is universal size although hose end is larger at 1/2" OD (Barb OD .555; neck OD .490) .  You can use either rubber automotive hose (1/2” ID) rated for vacuum and hose clamps, or 10AN stainless steel braided hose with AN fittings, depending upon how you wish to plumb it.  Requires a valve cover grommet with a 3/4" ID and will not fit the stock OEM grommet.

High Flow 40% increased capacity than PCV1 valve.  Works well with a stroker motor or shorter stroke high rpm race applications.  PCV valve starts to close ~1-2 in-hg

NOTE:  PCV Valve Flutter: The PCV valve may flutter at idle, and is not a problem.  It is caused by the repeated cycle of increased vacuum closing the pintle, and the opposing force of the spring opening it.  This back-and-forth oscillating motion causes the flutter.   It does not usually close completely, and when functioning properly, is a metered and controlled vacuum leak.  However, it is designed to close completely upon an engine backfire.  During normal driving conditions, the PCV valve pintle allows for greater or less flow, depending upon vacuum levels, according to throttle position and engine load.