Let's talk PCV systems

[Brad54]

I've got a '62 Suburban, originally from California. It has a closed PCV system on the 283. This has a sealed twist-on oil fill cap, a PCV valve coming off the fill tube, and the crankcase vent at the back of the block.
The open PCV systems have a vented push-in cap, a valve and the vent at the back.
Have any of you guys bothered putting the valve back in, have you omitted them, are they gone/missing/cannibalized over the years? When I got my truck, the crankcase vent was running to the carb base, the port in the oil fill tube was bare and open to the atmosphere (allowing unfiltered air and dirt into the fill tube/engine), and the port on the underside of the air cleaner lid was also bare and open (allowing unfiltered air/dirt into the carb). I've tracked down all the parts and have restored my closed PCV system (even though I don't need it in Georgia). What have you guys done?
I kept the closed system, because I think it'll help keep the engine a little cleaner...it's not uncommon for breathers to eventually allow an oil film to develop on the engine around them.

Thoughts?

-Brad

[Eagar1]

The closed system works just fine usually, but you need to keep an eye on the valve. What you want is a negative pressure situation so that your pistons and rings are not fighting the crankcase pressure. Some hot rodders or racers actually install a vacuum pump to reduce the pressure even more. They can actually pick up some hp that way. Other systems use a down tube that runs down along the chasis and creats vacuum as you move.

[Tomsriv]

The PCV system is a great system. If I recall correctly I believe it reduces HC emissions (unburned fuel) by 60% and it keeps the motor cleaner inside, AND it doesn't take away any power! You can't get any better than that.

[19GMC63]

I've always wondered about the PCV system on my motor. Does it really make sense to have one side going into the carb and the other a breather?


sorry for the thread-jacking, lol.

[rickf]

Same question as 19GMC63 ... It is the same setup I have, and I was told it is fine, and is an OEM setup. But it seems to me this creates an intake manifold vacuum leak.

[Brad54]

Actually 19GMC63 and rickf, this is exactly the conversation I wanted to start!
It doesn't create an intake leak, because the cylinders and combustion chambers are seperated and seald from the crank case--the lifter valley, crank, cam and oil pan. The piston rings seal the cylinders from the bottom side, the heads from the top.

Have a lot of guys here gone with custom engines/systems (valve mounted in the valve cover, for instance), or have people gone with the original oil fill tube and stock location for the PCV valve?

-Brad
-Brad

[rickf]

The combustion chamber and crankcase scenario is not the leak I mean.

What I mean is that the manifold is connected to the PCV valve, which is in a valve cover.
The space under teh valve cover is connected to the crankcase (it has to be, or it would not work to vent the crankcase).
So the space under the other valve cover is also connected to the crankcase.
In that other valve cover there is a filter "connected" to atmosphere.

So there is an air flow route thorugh the valve cover filter into the valve cover, through the crankcase, up to the other valve cover, and through the hose to the manifold.
It seems to me that qualifies as a vacuum leak.
But it must be that the flow is sufficiently restricted or otherwise accounted for, because it seems to work fine.

But it also seems to me that valve cover filter could be plugged off, and just let the crancase run with a vacuum. Is that not okay? Is that not the same as the "closed system"?