Ronnie Russell said:
What has high manifold vacuum got to do with oil flow? How is the oil getting into cyls? Why drill another vent hole in an intake that already has a much larger provision right next to it? Faster the rpm the more the pump delivers. Highway speed is relatively low. Less oil flow than high rpm .I will use the Offy without pcv and without added vent. Only time will tell. I will be using valve cover breathers and vented oil filler cap. To each his own.
I think you might have missed something here, Ronnie. The hole I drill, is not a vent. It is a tapped hole that the bolt threads into.
The "bolt", you ask ?
Yes. The one that retains the shield that I install.
High manifold vacuum has nothing to do with oil flow... unless you run a PCV system. OK, call me a tree hugger
... but I like PCV systems on a street driven engine... especially one that gets used frequently. PCV also helps remove acid contaminants from the crankcase... extending oil life... and bearing life.
So, what does manifold vacuum do ?
Quite simply, it draws in "pressure" from the crankcase. The higher the vacuum, the greater the difference in pressure between the manifold ( PCV system ) and the crankcase... the greater the flow through the vent at the back of the manifold, the PCV hose, the PCV valve, and the manifold plenum... which of course leads to that high speed flow into each intake port... into each cylinder.
So, you can decide....
Have a baffle/shield in place... and "vent" crankcase gasses into the intake system.
or
Have no baffle/shield in place... and "vent" crankcase oil into the intake system
???
Even if you do not use a PCV, "venting" to atmosphere without a shield at that opening, is going to draw oil out of the crankcase.
Highway speed, for most of us, is around 3000 RPM. Pretty decent amount of oil moving around over an extended period of time.
I won't say I told you so