Originally Posted by Cobra720
I've been curious about whether to run a PCV valve on one valvecover or not. I did alot of reading on this and everything is all over the map. I understand it purges the contaminated air from the crankcase which helps to keep the sludge from building up and oil clean. I run my Hotrod seasonal and change the oil often. I don't want any air leaking into my carb at idle. I want a clean idle and I need to keep my throttle plates open as much as possible to keep proper transfer slot exposure. Leaking air into the carb at idle will raise the idle forcing me to have to close the plates a little thus closing off the slots almost to nothing. I pull about 8-9 inches at idle also my plates are drilled. When I ran a vacuum gauge on the car and took it for a spin, the vacuum would move around depending what type of driving I would do [usually a little higher than 10 inches but as approach WOT it would naturally fall. SO I thought, I'll select a PCV valve that is closed at idle and open at other times. FORGET it they don't make them that I know of. So I went to Auto Zone and started looking at an assortment of them. Believe it or not I started opening packages ( you can do it without damaging them) and started sucking on them. ( I know it sounds stupid) but this is what I found out. They are all over the map. Some stick, some leak, some open very quickly and some you need to really suck on them to get them to open. How can you possibly buy one to stay closed at say 7 inches and open at say 10-20 inches?
Right now I put two breathers on the valve covers. I adjusted my carb and have everything perfect ( transfer slots, mixture screws and rpms) so now what?
Should I just leave it the way it is, or does someone know of a really high performance PCV valve I can buy ( without going to the High dollar evacuation systems) that is more tailored to performance engines.
Is a PCV valve even suppose to be open at idle?
For all I know I could be completely wrong on how a PCV valve is suppose to work on a HotRod, but I'm willing to listen to all thoughts on this.
"The PCV valve connects the crankcase to the intake manifold from a location more-or-less opposite the breather connection. Typical locations include the opposite valve cover that the breather tube connects to on a V engine. A typical location is the valve cover(s), although some engines place the valve in locations far from the valve cover. The valve is simple, but actually performs a complicated control function. 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. 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. spring tension. At idle, the intake manifold vacuum is near maximum. 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. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. With a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. At full throttle, vacuum is much reduced, down to between 1.5 and 3" Hg. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn in to the engine's intake manifold anyway."