Crankcase ventilation.

Bewy said
One reason PCVs get disconnected is because a bigger cam is installed in the engine, & these have less vacuum at idle. Not enough vac to pull in the pintle inside the PCV.....
So the PCV gets disconnected....

I've had engines with as little as 3hg and they have all operated a PCV properly. My current slant 6 only had 6hg and it works just fine.