Hidden PCV?

[_Drewfus_]

Hi Skip I know you are a Hemi expert, and was wondering what you think of using a PVC Valve in the valley cover of a 354 Hemi and routing it to the base of the carb and using the stock Oil fill breather as the air inlet for the PVC system, without having a vent in the stock Hemi valve covers.

I ran my hemi like that for just one year and every time I pulled the covers to set the valves, there was a milky brown film on the bottom of them.

I cut my chromed "IMPERIAL" valve covers for Offenhauser breathers (the same as the one on my O'Brien Truckers finned covers).

the breathers are on the front of the covers and I draw the air out through the draft tube opening in the valley cover

I've been thinking about this issue of late as I'm in the early stages of making a 'log intake manifold' for a 331 I've just bought, and looking at what to do with the valley cover breather/PCV wise.

Now whilst I've read the above, similarly I, am reluctant to cut the rocker covers.

If I may interupt for a moment with a few extra questions....

1.  "PCV valve REGULATES the air flow", why regulate it? why not just have breathers to act as an air intake and exhaust?

2. if I were to 'jump to conclusions' and suspect that the 'flow' of air is to make sure any and all condensation is removed from the engine, then on the Hemi (or whatever V8 ) is there a better flow prefference?

eg air intake from above the 'valley', exhausting through both rockers(or vica versa), OR, air in from one side(rocker) through the engine and exhausting to the other side.....

3. if on the Hemi I were to fit the breather intake to the valley pan, and then, at the rear of the rocker covers link a tube to a remote mounted PCV in an effort to remove the rising condensation from the highest point?

Appoligies for cutting in, but would really like to know the best way to approach the issue with the least visual intrusion(around the rockers) as possible.

Thanks,

Drewfus

[enjenjo]

The crankcase has to be ventilated because during the combustion process, there is a certain amount of blowby past the piston rings. There is also the pressure inside the engine created by heat, which causes the vapors in the crankcase to expand. One of the byproducts of combustion is water vapor, that also makes it's way to the crankcase. If left there, when the engine is shut off, the vapor condenses into liquid water, and drains into the oil pan, where it sinks to the bottom. there is also an emulsion of water and oil that coats the inside of the upper parts of the engine. This sludge, and the water in the pan, react with acids formed by combustion, that further break down the oil, and can actually etch the bearings, and other surfaces in the engine. With no ventilation at all, the crankcase become pressurized, and will actually blow out gaskets to relieve the pressure, causing oil leaks.

Before the use of PCV ( Positive Crankcase Ventilation) systems the crankcase was ventilated by a road draft tube, like your 331 has now. This system has one or more breathers on the top of the engine, that allowed air into the crankcase, and a road draft tube that was exposed to the moving air under the car, that pulled the vapors out of the engine using the Bernoulli principle. This system was inefficient at best, and of course was ineffective when the car wasn't moving. The system also dicharged raw hydrocarbon vapors directly into the air under the car, contributing to pollution.

In 1963 in the US, later in other parts of the world, the engine manufacturers started using a positive crankcase ventilation system. This consisted of a means of air entering the crankcase, a breather of sorts, with a filter to keep out dirt and contaminants, and a vacuum operated valve that passed the vapors into the intake manifold. The valve has a spring controlled seal, that has to be opened by vacuum to allow the vapors to pass into the manifold. This seal closes at low vacuum to keep from creating a massive vacuum leak, and a lean mixture. Therefore the valve has to be matched to the engine characteristics.

If you have no breather, there is no place for makeup air to enter the system, so the vapors will remain in the crankcase for the most part.  Without a PCV valve you create a vacuum leak that will affect the operation of the engine. So you have to have both elements in the system to make it work properly.

If you have both the breather, and the PCV valve on the valley cover, the air flowing through the engine will take the path of least resistance, and never completely scavenge the vapors from the rocker covers, allowing the water vapor to remain there. Is this a problem? It depends. The volume of the rocker chamber, the normal driving habits, ie. Short trips, long trips, ect., determine if it will work ok or not. FWIW, early PCV systems were set up with both the breather, and the PCV valve on the valley chamber, but within 3 or 4 years, all the manufacturers changed to valve cover mounted breathers, and PCV valves to combat sludging problems, under certain conditions. As a young mechanic in the 60's, I had to desludge many engines used as in town Police cars, or as Taxis, often with under 50,000 miles on them. This problem got much better after the components were moved to the valve covers.

[Skip]

Thanks for saving me fom having to type up a similar explanation.

As for the hemi, my setup of having breathers (intakes) on the front of each valve cover and the PCV drawing out of the valley cover via a modified stock Chrysler draft tube internal baffle isn't the optimum but it's far better than using the filler tube (into the timing case) as an air inlet.

Get as muchair movement as you can.

The optimum setup is in one valve cover, out the other.

[_Drewfus_]

Thanks for saving me fom having to type up a similar explanation.

As for the hemi, my setup of having breathers (intakes) on the front of each valve cover and the PCV drawing out of the valley cover via a modified stock Chrysler draft tube internal baffle isn't the optimum but it's far better than using the filler tube (into the timing case) as an air inlet.

Get as muchair movement as you can.

The optimum setup is in one valve cover, out the other.

Thanks guys,

excellent explanation, and it renforces the need to regularly change the oil (just in case).

Thanks,

Drewfus