PCV VALVE SYSTEM for 8BA with Early Intake Manifold

[V8COOPMAN]

Originally Posted by blucar

Reviewing the original question; Early intake manifold on a 8BA type of engine and the accompanying pix shows the PCV system plumbed into the rear oil fill/breather tube, no front fill/breather tube. If the copper tube running through the valve lifter chamber is the intended source of air flow from the lower crankcase, I doubt if that pipe would have the capacity to ventilate the engine.
Some Early Ford V8 pans have a 'draft' vent located in the front left of the pan. This vent must be closed off if a PCV system is installed on the engine.
Some people maintain that a closed crankcase system, PCV, won't work on a EFV8 engine because the rear main is not sealed, thereby the PCV will draw contaminates through the flywheel/clutch area and into the crankcase/engine.
I am getting ready to take the engine out of my '36, so that I can take it down to H & H to have the engine freshened up. It has not been touched since it's last rebuild in 1960. It is my intention to drill/thread a hole in the front portion of the Offy Super intake for a Ford 292 PCV which will plumbed into the vacuum port to the rear of the second carb.

Bill....I'm not sure that I understand the real point of your post here. Heard explained it rather clearly for you yesterday. And I'm not sure that you fully understand why the original road draft tubes were so large in diameter, vs the relatively small diameter of the tubing that PCV valves are plumbed-into. In fact, I'm beginning to wonder if you fully comprehend why pressure is created in the crankcase in the first place, and WHY there is such a necessity to relieve that pressure. I also have to wonder, since this article is so clearly labled "8BA", why you want to confuse matters referencing 'early' V8 oil pans with a 'draft' vent located at front....RIGHT? Same thing with reference to "not-sealed" rear mains on early V8s. We don't have this situation with an 8BA! And furthermore, you stated: "the accompanying pix shows the PCV system plumbed into the rear oil fill/breather tube". Well, the 'pix' DO NOT show that. The pics DO show the PCV valve & tubing ROUTED through that area, three to four inches below the breather tube itself, with the PCV valve being captured in a rubberized Dorman PCV valve holding fixture, which is part of a fully closed and sealed vacuum circuit (completely isolated from the fresh outside air supply). It's "plumbed" such that it makes way from the intake manifold vacuum source at a common plenum between the two carburetors, then entering the internals of the engine via a bulkhead fitting through the side of the 1" breather tube spacer. From that 90 degree fitting, the sealed circuit continues downward through the PCV valve (it's imperative to mount PCV valves vertically) and on to a compression fitting penetrating the now-capped-off exit tube which exits the oil pan chamber at the front of the valve chamber, and which ORIGINALLY connected to the original road draft tube. Check those pictures again! The pics below suggest ONLY the proximity of the PCV valve to the fresh air breather tube, which is now the avenue for injesting fresh air into the crankcase, and for adding lubricating oil.











First of all, crankcase pressure is created as a result of blow-by, the relatively small volume of combustion gasses that travel past the piston rings and begin to pressurize the lower crankcase, as well as any other areas of the engine which are common/open to the lower pan area. That pressure needs to be relieved because if not relieved, gaskets will begin leaking oil or even be blown outward from their sealing surfaces. In some cases, oil can even be pressurized out of dip stick tubes. Unrelieved crankcase pressure has even been known to deform oil pans. BUT....it usually takes some span of time for pressure to increase to that point if NOT relieved. This pressurization is not huge in volume like combustion exhaust is. In that regard, crankcase pressurization is not an instantaneous process.


Normally, in stock configuration, and in the vintage engines we're discussing here, fresh air is allowed to enter through a usually-capped breather (and many times oil-fill) tube. Fresh air enters only at such times that contaminated crankcase air (let's call it blow-by) leaves the engine via the open, large diameter road draft tube which has been carefully engineered and plumbed down to a point near the road. That draft tube (aptly-named) was designed to be down there for a couple of reasons. First was so that all those pesky fumes and smoke end-up as far away as possible from the sight and smell of us humans riding in the vehicle. But secondly, the end of that large diameter tube was projected into the airstream under the car such that as the vehicle moved down the road, the air rushing past the open end of the tube produces a vacuum via the Bernoulli Principle, effectively sucking the fumes out of the crankcase, at a rate that surpasses the fumes escaping via pressure build-up alone. Relative to the diameter of the draft tube, there is not a huge volume of blow-by being produced in the first place, but the larger diameter of the road draft tube is required to take best advantage of the air passing by the opening at the bottom of the tube to create enough vacuum to be effective. There is not very much purging of the crankcase fumes going-on with the vehicle stopped while idling, as that is one time the PCV valve is least-open.

So Bill, when almost all automobiles began employing PCV systems, that large-diameter road-draft tube disappeared, right? And true, regulated vacuum (via the PCV valve) positively sucked the fumes out of the crankcase as well as relieving blow-by pressure, correct? The entire volume of blow-by passes through that small diameter tubing (usually 3/8" to 1/2" dia.), which also means that ALL of it must pass through the PCV valve. I don't believe I have ever seen an automotive PCV valve with an orifice any larger than about 3/8" diameter. Go out there and just look at that hose nipple on the vacuum fitting at the rear of the valley cover on your Y-block (like the red one below). Not very large, is it?





You must remember that these engines produce a relatively small volume of blow-by (unless worn-out), that is easily evacuated when aided by the engine's manifold vacuum. You should also remember that dependent upon the level of vacuum being produced by the engine, the PCV valve is regulating it's volume of flow. Did you realize that a PCV valve is widest-open when the engine is producing the lowest level of vacuum?
Is there any other part of our dinky little PCV system here that I can attempt to further explain for you? We didn't go to the trouble of researching theory, doing some backyard-engineering, locating, procuring and documenting part numbers and supplies, nor take pictures and invest I don't know how much time laying this out and writing it up to tell everyone how it SHOULD be done. We only thought it might be kind'a cool to SHARE with others in a fairly concise manner, a plausible method which we devised to hide an ugly PCV valve, mounted in a vertical position, yet still affording the ability to service said valve without having to remove the intake for access. I don't believe I have it in me to make any of this any clearer. Promise....there was NO rocket science or gris-gris involved in this project. DD


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