Crankcase breather question

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AJ/FormS said:
The hole you see at the bottom is not the orifice, but rather the back-fire valve to prevent a cc explosion.
The actual orifice is at the other end. The valve is a tapered pintle affair, so depending on where it is at any one time, the tapered section controls the flow between minimum and maximum.


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thank you! That makes so much more sense, so when you use your mouth to try and apply a suction through one your not moving the orfice but rather the backfire valve. I was having a hard time understanding how it would flow with less vacuum when i was assuming the backfire valve was what is controlling the flow
 
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So weird question. I have a vacuum brake bleeder pump. If i were to hook the pump to the pcv valve, put my finger over the bottom hole of the pcv valve and pull a vacuum on the pcv valve, i could take my finger off then slowly release the pressure a little at a time while watching the gauge and see at what minimum value the pcv valve holds the vacuum to get the point at which the orfice is fully closed and partially open. Would that work?
 
AJ/FormS said:
It ain't rocket science; just plug it in and drive.

And no the hand pump won't work; it doesn't have the flow capacity. Maybe a vacuum cleaner..... lol
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lol thats hilarious, may hook it up to the shop vac. Jk. I know its a simple concept, makes a lot more sense now that i know the orfice controls the flow. I honestly thought there was just that one valve in there.
 
Hey at least i had enough knowledge and common sense to hook my pcv system up right, i know the purpose of it. Just never really got into the specifics of how exactly the pcv valve operates. They should of put that one on joe dirt. Hows a rainbow made? How does the sun set? How does a pcv valve work? It just does. Lmao

:rofl:
 
AJ/FormS said:
The hole you see at the bottom is not the orifice, but rather the back-fire valve to prevent a cc explosion.
The actual orifice is at the other end. The valve is a tapered pintle affair, so depending on where it is at any one time, the tapered section controls the flow between minimum and maximum.


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My pcv does not work like that its either open or closed -----------
 
71DodgeDemon340 said:
lol thats hilarious, may hook it up to the shop vac. Jk. I know its a simple concept, makes a lot more sense now that i know the orfice controls the flow. I honestly thought there was just that one valve in there.
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It would be interesting to find a way to test them.
 
nm9stheham said:
It would be interesting to find a way to test them.
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Aint got a clue , bought it from auto zone, off the wall. Had it on a hot 406 sbc at one time , got two of them left from diff. combinations .-------??
 
OK, well the odds are super high that it is a 2 stage with a check valve. There are all open and closed when the check valve comes into play; but just blowing into it back and forth only checks that, not whether it is a 2 stage.

This seems like an easy way to test these for the 2 stage operation:
  • Attach it to a car with a stock type high vacuum at idle and also attach a vacuum gauge to the intake tract
  • Put the open end of the PCV valve up by your ear (no, not INTO your ear LOL) and listen for the tone of the 'whoooshing' sound
  • Blip the throttle hard so that the vacuum drops way down
  • Listen for the 'whoosh' to increase and get louder when the vacuum drops
There are some oddities in the PCV world. One 4 banger engine I have, when stock from the factory... had nothing but a tiny restriction in a hose nipple running to the intake manifold. No check valve, nothing but that restriction.
 
famous bob said:
I have been playing w/ the pcv system some. I think the breather to carb hose deal will pull more out of the engine than we realize.
All street hemi`s came w/ a pcv on the drivers side and a breather hose to air cleaner on the pass. side . "Good enough for me !"
I just recently rigged up a oil mist catch can , because I had the junk laying around, it has a site tube to check oil level . Altho I haven't had any problems in that area , or any oil consumption , or blow by on the valve covers with just a breather on one side , will probly remove it after a while.
What I do wonder is , what effect my 6 pack scoop will have on the pass. side vent/breather to air cleaner deal. Any thots on that ??
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AJ/FormS said:
That's a good question, and IDK the answer. It took me several readings to figure out what you might be getting at. I guess yur thinking the scoop might pressurize the system at speed, which would then dick with the normal pressure venting at higher rpms. Am I on the right track? I think that's a valid thot and as I was thinking about it, an idea came to me; How about just Teeing a dump hose into that line down below the level of a valve cover. This would allow the system to work normally most of the time, yet as the pressure in the scoop rises with speed, simultaneously with increased blow-by from rpm , they just both together dump thru the Tee. Of course you might want to figure out a good place to dump it so it don't make a mess.
Or I suppose you could run a pressure vent elsewhere...... maybe jam it into the exhaust system. That would take care of the mess.....
Those pan e-vacs really work. I ran two of them with a working PCV on my 292/292/108 11.3 Scr combo, and never even gave it a thought, as to they might be fighting eachother at times. But for me, they worked so good, they pumped a lotta oil into my mufflers.

Course it just might be that CC pressure is higher than scoop pressure.... and then it would just be business as usual for the PCV system.
I suppose you could just measure the CC pressure at speed, with and without the hose connected to the air cleaner, and see what happens. Do not let the pressure in the cc rise above 4 psi, I have blown the camplug out one time.
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I can add to the question of the scoop adding pressure to your intake systems.
It totally depends on your hood shape and scoop height, but I can tell you most cars actually have a vacuum in the scoop when at speed.
A scoop would have to be higher than the smoke stream shown on these cars in a wind tunnel.

windtunnel.jpg


bosswindtunnel.jpg
 
nm9stheham said:
It would be interesting to find a way to test them.
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Simplest is to hook it to the engine with a flow gage.
Like I posted earlier its right in the shop manual - if you own an AMC.
upload_2020-2-1_13-52-44.png


Any shop that does A/C work will have a vacuum pump - not sure if they will all have enough flow capacity.
 
TrailBeast said:
I can add to the question of the scoop adding pressure to your intake systems.
It totally depends on your hood shape and scoop height, but I can tell you most cars actually have a vacuum in the scoop when at speed.
A scoop would have to be higher than the smoke stream shown on these cars in a wind tunnel.

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Exactly. Most scoops don't work because they are way too low and too far forward.

The more the front end is vertical, the higher it needs to be. The air hits the front end and almost goes straight up.
 
71DodgeDemon340 said:
lol thats hilarious, may hook it up to the shop vac. Jk. I know its a simple concept, makes a lot more sense now that i know the orfice controls the flow. I honestly thought there was just that one valve in there.
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There is just one valve in there; double ended and tapered, and spring-loaded. The spring is the calibration key that responds to engine vacuum, to vary the amount of flow. The orifice controls the max flow, and the seat the minimum
 
AJ/FormS said:
There is just one valve in there; double ended and tapered, and spring-loaded. The spring is the calibration key that responds to engine vacuum, to vary the amount of flow. The orifice controls the max flow, and the seat the minimum
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thanks sorry it was late last night when i saw the diagram, i thought i saw a separate valve
 
I have a old pcv valve im going to take apart to better familiarize myself with the inner workings
 
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