Agreed. The amount of suction for the total engine is between 18 and 20 inches of mercury, but for those of us who think more along the lines of pounds per square inch that is between 8.84 psi and 9.82 psi. So, the V-237 pulls out crankcase gases at about 0.98 psi. I would argue that it doesn't matter which direction the suction goes... from the valve cover or from the road draft tube location. Either way, the oil can mix with existing crankcase gases on its journey through the engine since all internal parts are coated with oil. The idea is to create a negative pressure where a slightly positive one exists. With no PCV, you have gases coming out of the valve cover AND the road draft tube which represents positive pressure. By adding a valve and connecting it to the intake, you have slightly (depending on the valve you use) negative pressure which pulls away the gases. (But only if the system is sealed. Valve cover and side cover gaskets aren't leaky, road draft tube port is sealed, and the dipstick has a good seal to the dipstick tube). Since this is all happening every second the engine is running, it's very effective.
I would also remind those of us who were there during the initial discussion years ago that we were all looking for the least invasive way to do this for all vintage 216/235/261 engines. The entire "Keep it Stock!" crowd who many of you are a part of didn't want holes in the vintage valve cover, or in the air cleaner, or in the road draft tube. When Dave and I and a few others engineered the system after lots of feedback from here, it was keeping that solidly in mind. With "Deve's PCV System" (which in actuality was a group effort) the PCV system can be removed, the road draft tube inserted and no harm, no foul.
Since the gases that are present are created on the bottom end as they are on the top due to friction, heat, oil and environmental characteristics, (thus the term crankcase gases) we did the best we could with the design Chevy gave us in the least invasive way. By inserting a freeze plug and grommet at the road draft tube port, we are sealing that hole completely which is important in closing the system for best performance for the valve. With about 1psi of actual pull, there is no chance of oil getting sucked into the valve or any other adverse effects with the added bonus of not affecting vacuum windshield wipers or brake boosters. This system works very well. Is it perfect? I am not sure any PCV system is perfect since you are combatting a problem that was created before the fact. (crankcase gases exist first). I only wish there was an easier way with our vintage GMC (stock) engines to accomplish the same thing. But a little effort and you can get it done anyway! Great conversation!
Research and how to make this system yourself is here:
http://devestechnet.com/Home/PCVInstall
