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Should I be using a PCV valve on a '69 350 motor? Currently using just open ventilation on the valve covers and oil fill pipe on the manifold. What advantage will the PCV give me and if I go that route should I cap off all other intakes to the crank case (the valve cover breathers and manifold breather)? Why doesn't a PCV valve act like a big vacuum leak?? I realize there's a check ball in it, but it still seems to me it would let a lot of air into the intake manifold. Thanks !!!
 

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Yes.
 

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Yes to the PCV valve. Valve in one cover with a breather on the other. The breather cap also doubles as a filler cap.
 

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They do act like a big ass vacuum leak but much more noticeable with a big cam with lower vacuum.

I tried tuning around different PCV valves but it was laughable. You shouldn't have to change your idle settings just to run a PCV valve.


Best to use adjustable PCV for hot rods. Dual Flow Adjustable PCV Valve ? M/E Wagner Performance Products
 

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Originally, the PCV valve replaced what was called a draft tube (just a vent to atmosphere) as an emission control device. It was intended to suck crankcase gasses into the intake and burn them, thus reducing emissions. The benefits of running a PCV extend beyond emissions, your crankcase will be kept cleaner with the fresh air being pulled through. The PCV system involves a valve calibrated to the application (they have different amounts of flow at various vacuum levels) in one valve cover and a supply tube in the other valve cover which was attached to the air cleaner (a breather can be used). So yes, you should be using one. As a side note...lower pressure in your crankcase (vacuum from the PCV system) reduces drag on the internal rotating assembly. Hope this helps a little.
 

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The most important thing with the PCV is ensure your engine has enough vacuum to pull the pintle valve in at idle.
Idle airflow for a stock engine is about 17 cfm & a correctly working PCV accounts for about 4.5 cfm of that. So not a big air leak. If there is a large change in idle rpm when PCV is hooked up, it means the A/F mixture was either too rich or too lean, depending whether rpms increased or decreased. This assumes engine vacuum at idle was sufficient to operate the PCV. Properly working PCV/mixture control should increase idle rpm about 30-50 rpm.
 

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this was mature technology over 50 years ago.

pcv in one V/C, breather in the other as stated by Mike in post #5.

one of the main benefits of a PCV system is that it pulls the water vapor out of the engine. Without one you end up with milky oil, looks like you have a leaky head gasket. Water is one of the main by-products of combustion. Also, sulphur in the blow-by gases combines with the water in the crankcase to form sulphuric acid. guess what it does to the bearings?
 
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