This statement from JohnZ has been 'working on me' off and on for a long time and I'm still not sure I 'get it':

https://www.corvetteforum.com/forums...post1587085690

Is this saying that 1964 (and later) Corvettes had the PCV valve reversed from 1963 ? (I don't have access to a '64 to check)
Was it located elsewhere ?

 

The pictures are correct. The text description of '63 flow is at least confusing and/or a little inaccurate the way I read it. The flow was reversed though. No big deal

 

The way I read John's post all he is saying is the 1963 PCV system is reversed from the 64-up PCV systems.

The 63 uses the PCV valve to pull from the rear of the block and the 64-up uses the PCV (or a restriction) to pull from the front of the block and allows filtered air back into the rear of the block.

 

This is the phrase I was referring to.

"from the oil fill tube into the front of the air cleaner,"

The fresh air flows from the air cleaner to the oil fill tube.

As stated, the pictures tell the story.

Fuel injection engines, '63 and early '64 pulled vapors from the back of the engine and fresh air entered through the air cleaner and into the engine through the oil fill pipe.

Late '64 and '65 FI engines drew vapors out of the oil fill pipe and into the front of the intake plenum. Fresh air entered through the rear of the block, fed by filtered air taken from the air cleaner.

When I say "early/late", I am referring to the 375R FI units. I've never seen one, never owned one but I think I'm correct there. Somebody will enlighten, I'm sure.

 

Yeah — maybe I’m over-thinking it.

 

I can attest to the 64/365 as I'm building one now. Air is pulled from inside the air filter, after being filtered, through a fitting in the AC base. A hose connects a relatively large metal pipe that is anchored to the rear of the intake and to the hole in the rear top of the block (old downdraft). Air from inside is drawn from a side connection on the oil fill tube, through a small hose to an orificed elbow fitting on the driver side of the Holley carb.
Will be getting to the 63 in a few months, hopefully.

 

Thanks all - I think I've worked through it... I don't do 'backwards' well...

Guess I should join D.A.M. (Members Against Dyslexia)

 

But then you'd be a DAMN - New Members Against Dyslexia.

Better than being an Dyslexic Agnostic Insomniac. Those poor folks stay awake all night wondering if there's a dog.

 

Here's the exact text from my "PCV 101" article, published 12 years ago in "Corvette Enthusiast" magazine, describing the function/configuration of the 1963 PCV system and the changes made to reverse the flow for 1964.

The 1963 “closed” ventilation system, used on all engines, used the oil fill tube as the “intake” side of the system, to admit outside air into the crankcase, and used a hose from the hole in the back of the block (previously used for the road draft tube) to the base of the carburetor as the “exhaust” side of the system.

At the “intake” side, a hose carried outside air from a fitting on the “clean” side of the bottom front of the air cleaner to a fitting on the oil fill tube. At the “exhaust” side, the hose from the vent hole in the back of the block had a PCV valve where it connected to the carburetor base. The valve was exposed to full manifold vacuum, which “pulled” outside air through the crankcase, carrying the hot vapors into the intake manifold to be burned along with the intake charge. The PCV valve is essentially a spring-loaded one-way check valve, which only allows flow through it in one direction under certain vacuum conditions.

The “closed positive” ventilation system used engine vacuum to force a continuous flow of fresh air through the crankcase, and burned the vapors as part of the normal combustion process instead of exhausting them directly into the atmosphere. This finally created a controlled ventilation system to reduce sludge formation, and reduced hydrocarbon emissions into the atmosphere.

Changes For 1964: Continuing development indicated that the system’s efficiency was improved by reversing the ventilation airflow so the “intake” side was through the vent hole in the back of the block, and the “exhaust” side was through the oil filler tube to the carburetor.

The “intake” side used a steel adapter and large-diameter vent pipe at the vent hole in the back of the block, connected by a large rubber hose to an elbow in the bottom of the air cleaner, so clean air was drawn from the air cleaner into the back of the block. Inside the air cleaner, a steel fine mesh screen was pressed over the stub on the elbow as a “flame arrestor”; this prevented a carburetor backfire from propagating through the vent tube into the crankcase, which could cause an explosion. The same type of flame arrestor technology is used for the air cleaner element on inboard marine engines so a carburetor backfire won’t ignite bilge fumes.

The “exhaust side” of the system was moved to the oil fill tube, which had a fitting for a hose to a manifold vacuum source at the carburetor; engines with Carter WCFB or AFB carburetors continued to use a PCV valve and fitting at the back of the baseplate. The 365hp engine used a Holley carburetor, with a slightly different arrangement; the hose from the oil fill tube connected to a 90 fitting on the driver’s side of the carburetor with an internal .090” restrictor orifice instead of a PCV valve. The orifice in the fitting was supposed to be cleaned with a fine wire at each tune-up interval; if the orifice became plugged, the crankcase ventilation system ceased to operate, and crankcase vapors would be driven up the rear vent tube into the air cleaner. The 1964 system design continued unchanged into 1965 for small-block engines.

Fuel-injected engines used the same basic design (“intake” from the air cleaner, and “exhaust” from the oil fill tube to the intake plenum), although the plumbing was different.

 

Superb explanation !

 

John, well explained. I've had one of Frankie's "wonder about" on the 64. When air flows into the back of the intake it goes through the "oil can separator" backward for it to work? Whereas the 63 flows correctly for oil separation. What prevents the air flow up the oil fill tube into the hose, into the carb from pulling oil from the cam cavity?

 

See post #4.

 

Kinda groggy today Mike, so not understanding.
My question in summary, air pulled from the rear goes through the "oil separator". Air through the front when reversed in 64 has no oil separator. Would seem to increase oil consumption.

 

I've been following this thread since yesterday and I don't understand all the confusion. You have it right.

 

If I'm not mistaken, at least some of the oil fill tubes that the vapors are pulled from have a baffle in them to separate the oil from the air stream. I'll go look here in a minute. Been a long time since I eyeballed an oil fill tube up close. Edit: Based on a sample size of one I had handy, I can't verify the baffle.

In any case, there is not a lot of oil flying around inside the oil fill tube compared to the rear of the block with the crank, cam and lifters throwing oil everywhere.

The post above was simply to point out that the FI intakes used two different directional flows, just like the carb engines.

 

My 64 250hp has the hose from the oil filer pipe to the rear of the carb but there is no pcv valve just a 90* brass fitting. I looked in the AIM and could not find any reference to this valve. Is there a picture available for this part and does it have any distinguishing # on it? Does the brass fitting have a internal that does this function?
Thanks Ric

 

http://www.chicagocorvette.net/diagr...d=1919&rc=1481

 

My wife tells me I can't find things with my eyes open, and she is right and this is another time I still can't see any PCV valve. The part at the base of the carb in the photo (b3735) is the brass 90* I was referring to, maybe I am misunderstanding the term valve mentioned by John Z. I was thinking along the lines of the type of valve that fits into the valve covers of later cars that has a rattle sound when you shake it. What am I missing?
Ric

 

Most cars used a valve that rattled. It was a spring loaded pintle valve. The fitting you should have is not just a standard brass fitting. It has a small restrictor hole in it that allows a small amount of vacuum bleed (leak) and draws air through the crankcase.

 

I'm reading this as the 64 365hp cars used the orifice, but YMMV.
If you DO have the orifice then note the scheduled clean-out instructions in the above article...