Finishing up a 292 Chevy install. Got 2 engines. Both had a different ventilation set up. Ive got both these set ups. The top set up I’m familiar with. The bottom, how does that work. I’ve got the air cleaner for the bottom with a paper element. An oil bath for the top but won’t clear the hood on the truck we put it in. The closed system air cleaner fits tightly together. Hard to separate the top from the base. Seems very restrictive but clears the hood. Anywho. Just curious.
The closed system doesn't let the vapors escape into the atmosphere, it burns them in the engine. The open system was used most of the 60s, the closed one 70s-80s. Either will work. If the engine is not worn out, the closed one will give you less blowby stink.
Had 150-160 for compression numbers. Doesn’t smoke. Was a junkyard engine we did a reseal on for a beater. the pvc one was mid 60s the other was mid 80s.
Constant suction on the engine, no outside vent. Just blow by and crank case gasses. I guess it’s more like a modern car. Making sure one wasn’t made up of mix matched components as we wrap up this swap.
Because the air must come thru the the intake air filter, I would think it's cleaner and better for the engine. If you're running multiple carbs, the earlier system is the best option.
The closed system came out in 1968. It draws air from a small filter located inside the air cleaner assembly.
The first system works well in high vacuum situations but in low vacuum when the throttle plates are open not so well so they vented into the air cleaner where there is high air flow to pull the fumes out.
Looking at the diagrams they are both the same with the exception that the top one only has an oily gauze in the filler cap to catch dust etc while the bottom one draws air from the clean air side of the air filter. JW
Getting ready to go thru a 67 292 with the earlier system. I don't see much difference in either one, although the later one is more environmentally friendly. You can also buy aftermarket vented pushrod covers, which some of the racers use for high revving motors.
Put a temporary 1bbl 3 inch air cleaner I had on it for now. got to modify the air cheaper mount to use the factory air cleaner. Looking for this “metered orface” anyone have a clue what’s it’s actually called.
https://www.jalopyjournal.com/forum/threads/are-all-pcvs-created-equal.1176669/ To confuse you even more. Just get the PCV valve for whatever engine that "metered orifice" drawing is referring to?
Well, it says valve assembly on the top pic and metered orface on the bottom my curious OCD brain wonders what the difference is
Tell us where that picture was used originally, and we'll have a start on it. But if it's just a random picture from the internet, that might not happen. fwiw, I did look in several parts books at group 1.745 and did not find any mention of a metered orifice. A PCV valve is a metered orifice, which changes size with applied vacuum level.
when posting sources, I like to start with a locally stocked item...saves time and shipping costs. but I expect Anthony has several old PCV valves laying around, that would work just fine.
Pic came from a Google search. Was posted on a thread asking about the different 292 ventilation setups on a gm truck forum
The 1969 truck parts book shows a few "VALVE, ventilator metering" or "VALVE, crankcase ventilator metering" in the parts listings. But I expect that drawing could be from a repair manual. And the terminology kind of blows with the wind on stuff like that. Pretty likely that it's a PCV valve.
PCV valve is a 'metered orifice'. It regulates, or meters, how much it ventilates via how much pressure is applied to the valve. Pressure differential will move the internal shuttle cock around which varies flow.
I always laughed at the word closed.. it should be filtered. When I installed aPCV system on my 56 Ford Y I found a Stant oil fill tube top with a 1/2” fitting and ran it to the air cleaner on the inside of the engines carb filter…..So I guess it’s “closed”
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