If you noticed, Deve was smart to do a leak test. If the system leaks, the PCV system is useless. In the early days, AC made a kit that checked vacuum level to see if the PCV was working. See attached picture. Everybody knows that cork gaskets (valve cover, side cover, oil pan) can leak as the cork ages...so an periodic on-going vacuum level test has to be done. If you are not willing to do this then don't install a PCV system.
Jerry's comment about the location of the PCV valve has merit. The picture shows the top of a road draft tube with the cover removed. Notice the holes inside. This design collects oil mist. Oil drips back down the tube and into the crankcase. Also notice the orientation of the PCV valve and right angle connector. Another deterrent for oil making it to the valve (I think everyone knows that oil can fowl PCV valve operation). GM designed the system for the early AD trucks. It works well on my 55. I can take my valve apart, clean and reuse.
Which PCV valve to use? See pictures (Chevrolet Master Parts List and AC PCV Catalog 660). At idle, vacuum is higher and overcomes the PCV valve's calibrated internal spring. Valve flow is at a calibrated minimum (too much flow can lean out the carburetor). At high speed, vacuum is lower and the PCV valve spring opens the valve a lot more. The valve is designed to work with a specific diameter hose. AC calls for CV670 hose which is 5/8". The diameter of the hoses, pipes and connectors can negatively affect the operation of the PCV valve so to be effective, use the sizes that the manufacturer recommends.
The amount of "blow-by" is not linear plus it gradually increases as the engine wears. Over time more vacuum flow is needed to remove blow-by. The AC PCV valve design is basically a crude on/off device to meet California and Federal emissions requirements at the time. There are better PCV systems if you are willing to install an oil trap and tune the PCV system to the condition of your engine and have a thick wallet.
In the end, why should we old truck drivers even consider a PVC system? The aroma of slightly burnt oil smell wafting up into the cab is not pleasant to some noses.
Last edited by buoymaker; 04/14/20226:00 PM.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
