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PCV Valves - testing

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steveg

steveg

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This site describes testing PCV valves to determine the best one for '50s chevy truck sixes:
https://devestechnet.com/Home/PCVInstall

Their experts say you want 1 - 3 inches of mercury suction from your valve. They describe measuring with a vacuum gauge in the dipstick tube. I think I'm getting around 3" because my needle starts around 2".
VacGauge.jpg
PCVvac5in.jpg


I'm using the CV727C valve specified by Norm Nock on P 98 of his Tech Talk book. This valve is for a 164 cu in Corvair.

Bob - I'd be curious how much vacuum yours is pulling through those small pipes.
 
My car is down for an oil change, pan swap and other maintenance--I'll try to measure when she's running again. I know I can hold my hand over the oil filler hole and feel suction at idle. My PCV kit came from BCS. I'd expect to get less than 5in if there was a filtered air source.
 
No idea how we would incorporate a filtered air source.

Nock says to solder the vent hole in the filler cap and I believe they give you a seal for the dipstick -- so the suction air intake must be entering where the rear crank exits the block. If this is the case, I'm guessing we would want the minimum suction in order to minimize the leaning-out effect of the air entering the intact tract.

I've ordered one or two PCVs for even smaller engines and will report back on their vacuum.
 
Last edited:
steveg said:
No ideal how we would incorporate a filtered air source.

Nock says to solder the vent hole in the filler cap and I believe they give you a seal for the dipstick -- so the suction air intake must be entering where the rear crank exits the block. If this is the case, I'm guessing we would want the minimum suction in order to minimize the leaning-out effect of the air entering the intact tract.

I've ordered one or two PCVs for even smaller engines and will report back on their vacuum.
Click to expand...

Interesting Steve. I think the idea is that the air source would be piston blow-by. I don't think we would want air flowing in the rear main seal with clutch friction dust in it. I'm working on a setup where the air comes from the air filter to the tappet cover, and air is pulled out the rocker cover T, through an oil catch can, through the PCV valve and into the manifold. I still have more testing to do.
 
John Turney said:
Interesting Steve. I think the idea is that the air source would be piston blow-by. I don't think we would want air flowing in the rear main seal with clutch friction dust in it. I'm working on a setup where the air comes from the air filter to the tappet cover, and air is pulled out the rocker cover T, through an oil catch can, through the PCV valve and into the manifold. I still have more testing to do.
Click to expand...

John - hopefully you'll have your setup at Healey Week in Monterey.
Piston blow-by makes more sense. My engine only has 50 miles on it - does even a new engine have a little blow-by?
 
John Turney said:
Interesting Steve. I think the idea is that the air source would be piston blow-by. I don't think we would want air flowing in the rear main seal with clutch friction dust in it. I'm working on a setup where the air comes from the air filter to the tappet cover, and air is pulled out the rocker cover T, through an oil catch can, through the PCV valve and into the manifold. I still have more testing to do.
Click to expand...

OT, a little, but I'm sending Blackstone a sample of my second oil change--first was break-in oil with 250m--after my rebuild. Don't know if they check for clutch dust or other contaminants, but the oil had 5,140 miles on it with 3qts of oil and 32oz of GM EOS added. Filter media had no appreciable metal or gunk on it.
 
steveg said:
John - hopefully you'll have your setup at Healey Week in Monterey.
Piston blow-by makes more sense. My engine only has 50 miles on it - does even a new engine have a little blow-by?
Click to expand...
I'm working on it.
I expect any engine will have blow-by. Once your rings seat, it should be at the minimum.
 
Hi Steve,

The source of the extracted gases is blow-by and vapor created by toxic water and oil vapor. The negative atmospheric pressure created by applying the vacuum will assist the oil slinger to pull back any escaping liquids. All this will be pulled into the intake manifold and gated into the rear cylinders for burning and extraction trough the exhaust. Because of this extraction path, I would strongly recommend the addition of an oil catch can to diminish any heavy oils from being pushed into the intake manifold.

This is a very inexpensive DIY that I proposed and built a while back but never added the PCV due to the confusion of which to select. I did, however, install the oil catch can and gaited it to the air cleaner.

https://drive.google.com/file/d/0Bx4EjcJmfaScU29Fa0d0TWNXcm8/view?usp=sharing

Ray(64BJ8P1)
 
I followed Knocks instructions too.

However, I could never make a PCV valve work proeryl on my engine and gave up
 
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