Would someone please explain to me why the 1954 cover has vents and the later covers do not.
The vented valve covers were part of the crankcase ventilation system to exhaust contaminated gasses from the crankcase. The road draft tube created a vacuum in the crankcase (@ 30 MPH) and the vented valve cover allowed fresh air to enter, replacing the fumes. Later, GM figured out that unfiltered air, sucking dust and other contamination into the engine, shortened the engine life. The first attempt at fixing this issue was to eliminate the vents and add a vented oil fill cover. Unfortunately filter media was adequate enough to filter only the largest particles and not the dust. Also this system on relied on speed and did not work at idle or lower speed typically seen in a city environment.
The answer had been an option in their truck fleet for years, a closed PCV system which got later incorporated into most engines by the mid sixties.
