opions requested on this PCV inst

[OLD AS I]

About to inst my intake manifold on my '46 rebuild, a 59, and see the pervious rebuilder installed a PCV on the underside of the intake, see pictures, appears to me its the same PCV that I've instd on Chevy V8's, 265, 283, 327's in the past, should I leave it or remove and plug ?

[outlaw]

Interesting, If it works that would be the most "kiss" (keep it simple) one that I have ever seen. I would be concerned with the valve being too low on the valley & sucking oil instead of vapors?

[deuce_roadster]

To make a PVC valve work well (no matter where you mount it) you should remove the pipe in the valley above the triangular vent on the right front of the pan and plug the hole with a welch plug.

[Ole Don]

I would like to see the PCV draw from all cylinders. The one in the picture seems to draw from two. I cut a hole in the exhaust chamber, then drilled into the area below the carb where the hole went in to both main runners. Then I used a long pipe nipple to get below the exhaust chamber, and made a sheet metal cover for the chamber. I drill and tapped to hold the cover on, then used JB Weld as a gasket, and around the pipe nipple. Then put on the PCV.

[SofaKing]

It looks as if the valve is installed upside down from how it would be installed on a SBC. If so I would not expect it to function correctly. Assuming the slug is held down (closed) by gravity and spring tension and pulled up (opened) by vacuum; installing it upside down would have the slug held closed only by spring tension while gravity is working against the spring. The result being it will open at a lower vacuum and remain open more than it should. This will be worsened because the leaning effect is limited to the mixture on two cylinders instead of all 8.

[JSeery]

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Where is the inlet air coming from with this arrangement? This does not look functional to me for several reasons. I would remove it and plug it. If you want a PVC system I would work with one of several established approaches.

[V8 Bob]

To make the pcv system work well, both intake planes should be connected to allow all 8 cylinders to pull on the valve, as Ole Don already mentioned. The intake end of the valve should be located at the front of the valley and up high, near the manifold, to minimize oil intrusion, similar to the original stand pipe location.
It's easier on your '46 59 to just drill the manifold above the stand pipe, install a pcv, and run the vacuum hose to a drilled source or plate below the carb. The stand pipe can then be removed and the block hole plugged, like deuce_roadster suggested.

[JSeery]

A PCV system requires an air inlet source (needs to be clean air), a path through the crankcase and a vacuum outlet connection. The PCV valve is to regulate the vacuum and prevent backfires from entering the crankcase. There have been PCV concepts posted in the past that are either non-functional or even worse, potentially damaging to an engine or reduce engine performance (basically a vacuum leak). Be sure you are using a concept that works!

[Jack E/NJ]

These theoretical flow diagrams always seem to show fresh air neatly flowing one way out of the air filter in to the crankcase. Then mixing with blowby and flowing one way out of the crankcase in to the PCV valve. I have yet to see a carbureted engine & PCV valve --- both in reasonably good shape --- where this theory holds at all throttles. How? By simply pulling the alleged fresh air hose off the air filter. Then see & smell the crankcase vapors & stink emanating from said hose in off-idle low-vac throttles where entrainment in to the carburetor air-fuel flow, not suction below the throttle plate, clearly becomes an important way of incinerating this crankcase pollution. Jack E/NJ

[V8 Bob]

Understanding the designed air flow through a '35-'48 flathead will help with properly installing a modern pvc system.

[OLD AS I]

thanks for all the comments, had it in mind to remove and plug it, this is the best place for answers in this hobby, ........... cheers

[blucar]

A PCV under the intake manifold, extending down into the engine without a baffle to prevent the PCV from sucking oil, is a sure failure. PVC' have to be serviced from time to time to make sure they are functioning properly. Having to remove the intake manifold to service the PCV is dumb beyond belief.
The installation of a PCV under the intake manifold was touted very heavily in the V8 Times about 25 years ago.

[V8 Bob]

Originally Posted by blucar

A PCV under the intake manifold, extending down into the engine without a baffle to prevent the PCV from sucking oil, is a sure failure. PVC' have to be serviced from time to time to make sure they are functioning properly. Having to remove the intake manifold to service the PCV is dumb beyond belief.
The installation of a PCV under the intake manifold was touted very heavily in the V8 Times about 25 years ago.

Dumb beyond belief is kinda harsh, as I and many others run the pcv under
the intake. Personal preference, for appearance sake etc., but not dumb.

[Jack E/NJ]

Originally Posted by V8 Bob

Dumb beyond belief is kinda harsh, as I and many others run the pcv under
the intake. Personal preference, for appearance sake etc., but not dumb.

And besides, you also remembered to put a baffle around it, right? Jack E/NJ

[Fourdy]

I realize this is the later engine but this is the way I set mine up and seems to work well. Use a valve that works in the upright position. Makes it easy to service.

[rotorwrench]

It looks to me that it would be kind of hard to maintain and troubleshoot. You would have to pull the manifold to do anything with it at all and troubleshooting could be difficult.

[Jack E/NJ]

Originally Posted by rotorwrench

It looks to me that it would be kind of hard to maintain and troubleshoot. You would have to pull the manifold to do anything with it at all and troubleshooting could be difficult.

I think the valve itself is on the back outside of the engine. I'm not sure about the do-hickey in the front valley near the draft tube. Jack E/NJ

[JSeery]

And once again, I don't see the air intake for this setup. There may well be one, but it is not obvious from the photos posted.

[Fourdy]

I shortened the original tube and welded a plate to seal it off forcing the flow to be drawn from below. The valve IS at the rear and outside the block. No need to get under the manifold.

Fourdy

[Fourdy]

Oops, air supply is the oil filler and a vacuum can be felt when running.
Fourdy