What confuses me about that system is that the hose on top the air cleaner seems like the carb would suck air from the valve cover rather than the other way around.
In other word it looks like crankcase air would be drawn from both hoses with no fresh replacement air.
The hose from air cleaner lid to rear of valve cover draws in filtered fresh air into the crankcase through air cleaner and valve cover. There is slight suction at the rear valve cover fitting when that hose is removed while engine is running.
Crankcase blowby is pulled from the front valve cover hose to intake manifold vacuum through the one way PCV valve, routing blowby into the engine’s cylinders to be burned. The road draft tube is removed and the orifice is plugged. In this closed PCV system, the crankcase operates under negative pressure.
Can’t argue with success. Trust the GM design?
