2x4s tunnel wedge and PCV

[Michael C Henry]

are all PCV valves pretty much the same? If they are then why so many different applications? A lot of the valves look the same ,if they wern't still in the package you couldn't tell one from another.. Some have addon plumbing. Is there really a difference or just find one that fits?

[speed220mph]

Michael: Positive crankcase valves are calibrated for specific engines. The PCV system on an engine is a controlled vaccum leak as are carburetior or FI throttle plates. The bigger the engine, the more air--crankcase vapor--must be evacuated by the PCV valve. Therefore, PCV valves are calibrated to the requirements of the engine. However, if you choose a valve which was used on a larger engine such as 6--8 liters, one valve will work.

The thing you hear when shaking a PCV assembly back and forth is a spring-loaded shuttle valve. This valve is forced against a spring by manifold vacuum and crankcase pressure. Thus, it maximum flow restriction at idle and wide-open throttle to limit air/fuel mixture leaning. The spring pushes the valve open to provide maximum flow during part-throttle operation. So, if your engine is jetted toward the lean side, the addition of a PCV system will require slightly fatter jets.

[Carnut427]

Originally Posted by Michael C Henry

are all PCV valves pretty much the same? If they are then why so many different applications? A lot of the valves look the same ,if they wern't still in the package you couldn't tell one from another.. Some have addon plumbing. Is there really a difference or just find one that fits?

If you check the application guide for a specific year, you'll usually find that all V8 engines of a certain make used the same PCV valve; 6 cyl engines usually used a different one. This is true for both Ford and Chevies, so the difference is mainly what will fit; I'd personally stay somewhere near the same year as the engine you have in case things such as computers etc. affect them. Don't know that they would, but just to be safe...
JMHO,

Dan

[fsiewert]

PCV valves are very different. Not just in size but in the amount of vacume it takes to open them up. The theory of the PCV valve is to create a vacume in the crankcase, valvecovers, lifter vally, so oil will not try to force it's way out of the gaskets and past seals and rings. the vacume is created from intake manifold vacume being used through the PCV valve. When the throttle is opened manifold vacume drops and the PCV valve closes to keep the vacume in the crankcase, to keep the oil in.

Readers Digest Condensed version.......
PCV won't work if:
Too much cam...not enough manifold vacume
Too much blow by past the rings
PCV valves are rated by vacume so you may need a different pressure PCV valve.
Some are spring loaded and some work on gravity..make sure they are in the position intended.
They won't suck at WOT (wide open throttle) Not supposed to.
The hookup to the manifold should be into the main plenum of the manifold because there is a most constant vacume there. Not a manifold runner. (too many pulsations) That's good for Vacume brake booster.
The vent should be in the opposite side valve cover to vent the WHOLE engine.and the higher the filter the better. That's why most are vented from the aircleaner. Clean air goes in that tube and out the PCV and is burned up in the combustion chamber with the air-fuel mix.

Now that I have truly mixxed you up, you should know everything there is to know about PCV valves.
Fred

[Mr427]

Hi!

I have been reading the posts above and I see some really nice looking systems that you are using for crankcase evacuation.

The positive crankase ventilation system was mandated by federal law in september 1966. Its sole purpose is to capture the very toxic mixture of residual air-fuel mixture that gets blown by the piston rings and into the crankcase, plus airborne lube particles that form insde the crankcase. It is a very violent place to be on any given day!

The PCV valve must be located, either in the center of the intake manifold or on either valve cover. It must be completely airtight, mounted in a gromet or pressed into a sealed container like in the pictures of the Summit setup above. This is where air gets sucked out, but only as far as compression pulses will open the check ball inside the valve casing, assisted by the engine vacuum signal.

If you suck out air, you need to have a place for it to get sucked in too. That place is the breather on the other side of the engine, or as on older FEs, through the filler / breather cap on the filler tube on the intake manifold. This, however is not an ideal setup. If you want maximum cleanup effect, you really need to have the exit and entrance on the valve covers. This is due to the fact that oil mist, gasoline fumes and water vapors tend to rise to the roof of the building, i.e. the valve covers. Since the FE with its Cobra LeMans or Baldie valve covers is one very tall building, this is where your culprit is going to reside and cause a mess, causing oil stains and what not all over.

So, in my view and from what I have read, the valve covers need to be the north and south borders in this war.

The PCV valves are made in a myriad of configurations. What varies is mostly diamter and weight of the check ball. This is regulated by the vacuum signal that each particular engine is known to have. That means STOCK engines that idle smoothly AND have a regualr vacuum signal at 650-700RPMS.

As you get into more aggressive cam profiles, the vacuum signal starts to change and deteriorate in more ways than we can count. As we get into degree territories above 235-240° @.o50 on the FE, you need to look at other options. Notably vacuum pumps (with aggressive cams and low pressure piston rings) and / or oil accumulators and scavenging systems that operate on header collector negative pressur. But on those applications you are always having to endure very discomforting and potentially deadly vapors inside your cars as you sit at the local stoplight.

The PCV system is the single most effective, least expensive and most reliable method of pollution control ever installed on an internal combustion engine.

bye

[Carnut427]

The rush of the fuel/air mix by the PCV hole in the intake, carb base plate, where ever, creates a vacuum on the PCV valve, so that the PCV system also works under acceleration, and there is enough vacuum under most other conditions, such as cruise, that it's actually working most of the time. At some point in spirited acceleration the PCV system may not be able to handle all the blowby. This is why you see puke tanks, scavenging systems that operate on header collector negative pressure, etc.
My 2 cents...

Dan