Non-vented valve covers and PCV

[MaineShark]

There are a lot of valve covers that don't have vent holes.

That leads to a few interesting topics/questions:

1: The crankcase needs to be vented. Preferrably, it needs to be evacuated (ie, connected to a vacuum source, to remove gasses forcibly). I've seen examples of cars which had a hole drilled through the intake manifold, into the valley, and another into the plenum, with a hose connecting them.

Will that properly vent the crankcase?

Would it be possible/practical to machine the hole for a PCV valve, rather than a hose barb, to have the proper operation? It's my understanding that the PCV valve operates as a check valve, so that crankcase doesn't suck air backwards through the vent. I would think that having the air&fuel mixture drawn into the crankcase would be a bad thing...

2: It's also my understanding that the valve covers need to be vented. The driver's-side one is vented by the PCV valve, and the passenger's-side one is vented to the air filter by a short hose (at least, that's how mine is set up). Wouldn't running non-vented valve covers present a problem, in that case?

3: How do you add oil? Similar to the first question, would it be possible to add oil through the cam/lifter valley, using a hole in the intake manifold?

Non-vented covers do present a much cleaner look, but these seem pretty important issues to address.

Joe

 

[Tom Bryant]

Non-vented valve covers are for use with older engines with the oil fill tube in the front of the intake manifold and a road draft tube or pcv fitting at the rear of the block. Newer blocks aren't cast this way anymore. On factory pcv systems the pcv valve allows crankcase pressure to be relieved by intake vacuum or high crankcase pressure (bad ring blow by) into the intake. The valve does act as a check valve. The hose to the air cleaner allows air to be drawn into the crankcase as the pcv is drawing it out. If you suck air out you have to let air in to complete the flow.

Some non-vented custom valve covers have knock out plugs or are otherwise marked to drill for pcv and oil fill cap installation. Aftermarket breathers are also available to mount on the valve covers. Bottom line is the engine must be vented.

Tom

 

[Ken]

Joe, I don't know if you want to do it this way, but I eliminated both the vent and the PCV and simply vented my covers to a remote breather tank--$29.99 through Summit.

_ken

 

[woobie1966]

beautiful engine ken!!! how does the remote system work? do you need to plumb into the side of the valve covers or can you buy them that way?

once again, nice engine... well done but not overstated
mike

 

[Ken]

I tapped the holes for the PCV and vent that were there already. Actually, I had to have the manufacturer open those holes when I bought the covers; there were no holes as cast. We opened them and baffled 'em, then when I went to this system, we threaded the holes for 3/4" NPT threads and used an 3/4" NPT to -10 AN fitting..

Thank you for the compliments.

_ken

 

[MaineShark]

I don't really mind having the crankcase vented to the intake. What I'd like to do is eliminate as much of the clutter as possible.

So, how's this sound?

Drill holes in the heads, just below the valve cover, at the back end of each. Run a tube across, connecting them, with a Tee-fitting in the middle, and a tube from that to the air filter, or a separate breather. Inside, there would need to be a tube connected to the same place, which would make a 90-degree turn and go up toward the top of the valve cover (but with a gap). That would keep oil out.

That covers getting air into the engine.

Then, machine a hole in the intake manifold (the portion that covers the cam valley, not the portion that has air or water passages in it), to fit the PCV valve. Tap a second hole into the plenum and install a hose barb. Run a hose from the barb to the PCV valve.

That covers getting air out of the engine.

That should make it extremely easy to get the valve covers off, and keep things nice and clean, since all the piping would be back out of the way, under the air cleaner.

The only question then is oil.

Is it possible to add an oil fill tube to the intake manifold, like the older engines? I'm planning on going to an Edelbrock Performer Air Gap, so that should make things eaiser (since the intake runners are separate from the valley cover). It looks in the picture like one could be run in right behind the thermostat housing. The tube would need a few bends, but it would also add a bit of nostalgia to the engine, I think.

Ken: I think my next 'Vette is going to look much like that one. I'm trying to keep this one a sort of blend between modern and older technology. In 8 or 10 years, I'm hoping to get a '73 and do something similar to Chris's "Killer" - a total hot rod, with little concern for originality. Going to be a lot of hoses and wires, I think

Joe

 

[Tom Bryant]

A machine shop can bore a hole in most intakes where the tube used to be. Just get an oil fill tube from Paragon or out of an old small block manifold. Put a chrome breather cap on it and you have also taken care of getting air into the crankcase; pressure out too to an extent.

Tom