The "Heavy Duty" was probably the term used for application on big trucks back in the early 50's (also WW2) not that the valve itself is heavy duty. Big trucks were the ones that usually eat a lot of dust and sand like during construction. Also the military working in the desert or fording a river. The valve was called crankcase ventilation. Fast forward in time, the California law required PCV (Positive Crankcase Ventilation) because of the severe smog in that state. The idea was to have an engine that is sealed-up. No leaking rocker arm cover(s) and lifter galley side cover to let engine vapors escape. Clean air in through air cleaner and combustion vapors and gases go out to the intake. AC made checkers (CT-1, CT-2 and CT-3) that tested the effectiveness of the sealed system. Hot Rod (Jerry) is familiar with this and installed a few of these retro kits in his day. Then comes the Federal (EPA) requirement for all cars and trucks in the USA.
I also have the metal tube from the road draft (actually crankcase tube, no drafting) to the intake adapter. Metal elbow with sealing pad on the valve cover and air cleaner. 5/8" hose between the elbows. It's important to have the correct diameter hose and metal tube for the flow through the CV 469.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
