Those cans located in the valley are there to keep the big chunks of oil from getting out through the draft tube, or the PCV valve when so equipped on the mid to late 60's engines that pulled air from the vent at the rear of the block next to the distributor. They worked adequately from my experience after seeing what happened if the under valley can was left out either by accident, or because of a person not knowing why the separator can needed to be there in the first place. When a PCV valve was hooked up to the rear vent without that can installed, an instant smoke screen occurred. Never saw what effect a can being left out, or if I did I didn't notice, any smoke or oil loss on a car equipped with a road draft tube.