Now this one absolutely baffles me... I'm getting my 1978 L28 up and running again and I recently replaced my pcv valve... Just having one issue. WHERE DOES THE PCV VALVE CONNECT TO?! I've attached two photos.. The first photo indicates where I expected to find the crankcase ventilation pipe that leads to the pcv valve. The second image is MY engine block... It looks like that breather pipe that supposed to be coming off the side of the block is "plugged." What do y'all think. If it was plugged, why would this have been done? Or am I just looking in the wrong spot? Thanks!   

Just now, Zed Head said:

I dont see that pipe protruding from the block in that diagram. So I should be looking to connect in a different spot?

From what i can tell, I'm supposed to connect the breather hose to that spot that appears to be "plugged" on my engine block.

Looks like somebody plugged yours with a core plug (aka "freeze" plug).  That's the spot.  Should be a piece of screen behind it.

Some people remove the PCV system and just put a breather on the valve cover.  Might be why yours is blocked.  Looks cleaner.

The drawing  that I pasted is not correct as far as the details.  The orientation of the pipe is wrong among other things.

Edited April 8, 20204 yr by Zed Head

2 minutes ago, Zed Head said:

Looks like somebody plugged yours with a core plug (aka "freeze" plug).  That's the spot.  Should be a piece of screen behind it.

Some people remove the PCV system and just put a breather on the valve cover.  Might be why yours is blocked.  Looks cleaner.

But even if someone wanted to remove the pcv valve, the crankcase would still need to "breathe." I've seen people put filters over the hole, but never have I see it blocked off completely.

The crankcase is connected to the area under the valve cover through the oil drain passages.  The reason for having two ports is so that the gases have a flow path, to push the exhaust gases and vapors out.  It's shown by the arrows in that drawing.  That's why it's called "positive" ventilation.  With just one port, you get pressure and vacuum relief but no flow.

3 minutes ago, Zed Head said:

The crankcase is connected to the area under the valve cover through the oil drain passages.  The reason for having two ports is so that the gases have a flow path, to push the exhaust gases and vapors out.  It's shown by the arrows in that drawing.  That's why it's called "positive" ventilation.  With just one port, you get pressure and vacuum relief but no flow.

So do you suggest leaving it alone? What are the pros/cons of deleting the pcv? How would the engine accommodate potential "blow-by?"

it just vents thru the open port on top of the valve cover (put a filter on it so junk does not go down). Down side is you will not pass emissions if you have a state that test for that. I suppose if the filter gets clogged you could build up pressure in the block, maybe blow out a main seal, if the blow by was bad. Cant see any upside.

Edited April 8, 20204 yr by Dave WM

2 minutes ago, Dave WM said:

it just vents thru the open port on top of the valve cover (put a filter on it so junk does not go down). Down side is you will not pass emissions if you have a state that test for that. I suppose if the filter gets clogged you could build up pressure in the block, maybe blow out a main seal, if the blow by was bad. Cant see any upside.

Here's the thing, my current setup has doesn't have a filter on the valve cover. I have the stock hose that connects somewhere around the throttle body. My point is that it's not open. Is that a problem? I didn't think it would run with the valve cover hose taken off. If there's not upside, I don't understand why someone blocked off that breather valve.

I've always considered this little gap as a way to connect the valvetrain and the crankcase.  I got worried about blowing out the rear main when I first started fooling with a rebuild and removing stuff.  We don't do the smog test here.

The yellow circle in this google image.  That's one without the front cover.  The head hangs over too so it's an open path from the valve cover to the oil pan, in my mind. 

The two downsides to just having the hose connected to your intake system on the top is that the oil will get contaminated faster, and you'll probably gum up the throttle blade, AAR, and intake manifold faster because the crankcase fumes will fill up the intake system when the throttle is closed.

You can spend a lot of time trying to figure out a PO's work.  It's fun if you're in to psychology.