Here are a couple of links to past threads regarding PCV systems.  Using the search function will bring up a bunch more.
Crankcase evacuation
Why a PCV valve or system? 

Lorena, Texas (South of Waco)

if the front seal quit leaking, now you are moste likley sucking dirt into the crank case threw the seal,as it is desighned tohave some presure in crank case,as well as inhibiting oil drain back. you should not havea vacume in the cranke case. ideal would be a minor amount of crank presure. just studey modern pcv equiped withpcv. they all have access for air to enter and stop vacume 

Roger, perhaps I worded that poorly. The Offy I had years ago had two openings under the center carb, that then somehow connected to the runners to the valves. I never cut one open to see how it worked. I was told the Edelbrock's went straight to the runners, but I never owned one. Long time ago, and getting OT.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

I think it will work at basically manifold pressure,
and yes my front seal has stopped its weeping.

I tried it because I was unsure of vacuum leaks and EFI tuning issues I was having, but if it's going to cause long term issues I will change it back. It's still however able to pull through the dipstick.

Set up properly the PCV lowers the crankcase pressure a slight bit, nothing like the vacuum pumps though. A resulting side benefit is reduced oil leaks since the crankcase pressure is below atmospheric.

Anyone know of the effects of vacuuming the crank case as I read something on pumps made especially for this to help the rotating components spin freer. I guess to much either way would cause issues.

Thats the type system I have on mine. The original air cleaner I found to use already had the hole in it so I just used it. When we were forced to add the PCV system in CA some kits came with a block off plate for the road draft tube and others came with a tapered rubber plug to stick in the tube. Never had a problem with the PCV system but then they came out with the NOX device wich was a piece of crap..

I would think the air being pulled through the crank case into the cylinder would glaze the bores over the crankcases reduction of drain back. Which is why there is a gauze filter between pcv and crankcase.
Yet now that I think of it there is usually a breather to the airfilter.

I would think the air being pulled through the crank case into the cylinder would glaze the bores over the crankcases reduction of drain back. Which is why there is a gauze filter between pcv and crankcase.
Yet now that I think of it there is usually a breather to the airfilter.

It's been a lot of years, but IIRC, the Offy manifold has the carbs on a plenum, and openings under the center carb to the lower plenum with the ports to the valves. Set up as a dual plane. That's why the Edelbrocks were somewhat more efficient. So the oil vapor ends up in the same place. I used the center opening for the PVC, and the back for the brake booster and the vacumn gauge.

Also, depending on your driving conditions and air cleaner, if you can find a filler cap with the sealed bottom and the tube on the side, run that into the air cleaner. On the filter side. Under high vacumn cruise conditions, it does a little better job of filtering the incoming crankcase air than the wire mesh in the open vented cap. And less oil smell in the garage. Fairly early on, we went to those closed systems, driven by CA air pollution laws, I think.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ