I have tested various PCV valves to determine which perform 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.
The following two PCV valves function better at a lower vacuum signal, but still open once the engine vacuum changes during all-around operation. They both begin to close at a lower vacuum signal of ~1-2” hg. One is standard flow and the other is high flow. The high flow unit increases flow by 40% over the standard flow unit. It works well with a stroker motor, or shorter stroke, high rpm race applications.
1. Standard Flow: http://stores.hi-potek.com/pcv-valve...vacuum-signal/ Grommet end is universal as well as hose end at 3/8” OD; it fits the stock plumbing. You can use either rubber automotive hose (3/8 ID) rated for vacuum and hose clamps, or 6AN stainless steel braided hose with AN fittings, depending upon how you wish to plumb it.
Standard Flow Unit
2. High Flow: http://stores.hi-potek.com/high-flow...vacuum-signal/ Grommet end is universal size although hose end is larger at 1/2" OD. You can use either rubber automotive hose (1/2” ID) rated for vacuum and hose clamps, or 8AN stainless steel braided hose with AN fittings, depending upon how you wish to plumb it.
High Flow Unit
A comparison of the standard flow PCV valve and the high flow PCV valve:
High Flow on Left
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 should close completely upon an engine backfire. Under normal operating conditions, the PCV pintle allows for greater or less flow, depending upon vacuum levels, according to throttle position and engine load.