![]() At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn into the engine's intake manifold anyway.An oil catch can is essential on a performance vehicle to protect the engine from elevated levels of crankcase blow-by accumulated from aggressive driving. At full throttle, vacuum is much reduced, down to between 1.5 and 3" Hg. With a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. As engine load increases, vacuum inside the valve decreases proportionally and blow by increases proportionally. It is at this time the least amount of blow by is actually occurring, so the PCV valve provides the largest amount of (but not complete) restriction. At idle, the intake manifold vacuum is near maximum. With the engine running, the tapered end of the cone is drawn towards the opening in the PCV valve by manifold vacuum, restricting the opening proportionate to the level of engine vacuum vs. An internal restrictor (generally a cone or ball) is held in "normal" (engine off, zero vacuum) position with a light spring, exposing the full size of the PCV opening to the intake manifold. The valve is simple, but actually performs a complicated control function. A typical location is the valve cover(s), although some engines place the valve in locations far from the valve cover. Typical locations include the opposite valve cover that the breather tube connects to on a V engine. "The PCV valve connects the crankcase to the intake manifold from a location more-or-less opposite the breather connection. We'll then I guess we will both agree to disagree. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn into the engine's intake manifold anyway." It is an "open system" in that fresh exterior air is continuously used to flush contaminants from the crankcase and into the combustion chamber."Ī drilled out hole is no longer calibrated leak. The PCV system just diverts a small percentage of this air via the breather to the crankcase before allowing it to be drawn back into the intake tract again. All the air collected by the air cleaner (and metered by the mass flow sensor, on a fuel injected engine) goes through the intake manifold. The PCV system is not a classical "vacuum leak". Instead of the gases being vented to the atmosphere, gases are fed back into the intake manifold, to re-enter the combustion chamber as part of a fresh charge of air and fuel. ![]() ![]() "The PCV valve is only one part of the PCV system, which is essentially a variable and calibrated air leak, whereby the engine returns its crankcase combustion gases to the air intake. Click to expand.We'll then I guess we will both agree to disagree.
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