While I never like to get into the middle of a good whizzing contest (I am lying. I just make sure that I stay out of the way of the crossing streams!),
HRL hit the nail on the head, especially with these old blow-by prone engines. You need maximum crankcase evacuation at mid to full throttle. The downdraft tube provides that, while the PCV system does not.
This commode-like post has enlightened me about where the schmutz, which accumulates on that small maxi-pad inside of the air cleaner (newer vehicles than ours) comes from. I could never grasp why it would collect there given that the flow was supposed to go the other way. Now we know. Thank you "King"
Carl
There is no check valve so air flow could go in either direction.
The "maxi pad" was able to get coated from vapors making them wet as the vapors condensed.
Being wet and they were exposed to unfiltered air the dirt stuck to them.
The PCV has a calibrated orifice so even when the spring tension can not be over come there is still crankcase ventilation. No matter what engine speed or road speed is. Plus there is no downdraft tube to drip oil on the driveway or garage floor.
Downdraft tube has no positive airflow without the car moving for no pressure differential will be created.
Then do not forget whether PCV or Downdraft Tube the engine still has a breather cap so there will not be excessive pressure built up.
Even my 1935 Buick had a louvered vent on the rear side of the valve cover.
