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My PCV System
Posted by: DAVECS1 ()
Date: August 07, 2018 11:05AM

I had a PM this weekend asking about my crank case venting system, as I had mentioned it was modern. I guess I should specify and say it is modern compared to 1964. I put together a little diagram and figured I throw it up here for all to see, in case anyone else wants ideas for tinkering.


1964 Monza Convertible
110 4 speed
Peoria, IL




Edited 1 time(s). Last edit at 08/07/2018 11:07AM by DAVECS1.

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Re: My PCV System
Posted by: toms73novass ()
Date: August 07, 2018 11:14AM

Thanks for the diagram. thumbs up

On the factory setup is there anywhere it pulls air through the engine or is it just sucking against a sealed volume?

-Tom


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Re: My PCV System
Posted by: DAVECS1 ()
Date: August 07, 2018 11:27AM

I believe it is just sucking against a sealed volume. One of the more senior Corvair experts may know something different.

I think the vacuum is pulled through an orficed opening on the vent tube and the big end goes to atmosphere. I am pretty sure that is the only opening to the crankcase besides the oil cap, which is why I vented it.

My oil and engine seem to stay alot cleaner.

1964 Monza Convertible
110 4 speed
Peoria, IL

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Re: My PCV System
Posted by: 66vairman ()
Date: August 07, 2018 01:11PM

Folks like to reference the "V" engine system, but in fact it works the same as the Corvair system. It is a common misunderstanding that air ALWAYS travels in from the air cleaner and collects fumes drawn into the PCV metered valve (orifice on later Corvairs) by manifold vacuum.

In fact on BOTH the carbureted "V" engines and the Corvair, the air pressure at the PCV or orifice must be normal air pressure with engine manifold vacuum on the other side. This allows for a fixed carburetor idle mixture.

A lack of engine blow-by (at idle) is compensated with air pulled in from the air cleaner. This allows a fixed idle mixture from a carburetor to be used (new EFI systems compensate).

When piston blow-by gases exceed what can be pulled into the manifold (WOT - low vacuum and high load) the excess fumes go to the air cleaner and are drawn into the carburetor.

The path to the air cleaner is meant to be two way. Keep the PCV system clean and it works fine.

Over the years there has been experimentation with using engine vacuum to lower crankshaft "windage", but I haven't seen any proof it's effective for "normal" cars driven at mostly modest power levels. Racing is a different story.

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Re: My PCV System
Posted by: Richard ()
Date: August 07, 2018 01:45PM

To add to 66vairman's post.

Your v8 representation shows a Closed PCV System. Your vented oil filler cap Changes your System into an Open PCV System, which is something Chevy never used on any Corvair.

The air cleaner hose on the Corvair with orifice or PCV valve will have blow-by fumes/air passing in either direction, depending on a mount of blow-by and vacuum just as with the closed V8 system.

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Re: My PCV System
Posted by: DAVECS1 ()
Date: August 07, 2018 02:48PM

This is different from my understanding. The PCV valve I am using is closed at high vacuum (idle or engine braking). As the manifold gets closer to atmospheric pressure it begins to open up. The low vacuum then pulls fresh air from the the breather side. In the case the pressure in the case is high, both the pcv and breather are capable of spewing fumes. In this instance it would be good to be plumbed to the front of the throttle blades, as the venturi effects could pull the fumes into the engine. I may look into doing this, now that we have discussed it. Gonna need a new oil cap darn it.

1964 Monza Convertible
110 4 speed
Peoria, IL

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Re: My PCV System
Posted by: MattNall ()
Date: August 07, 2018 03:06PM

There used to be a nice simple vacuum meter for PCV systems that were open...

You pit it over the air intake.... and watch the needle.. 2-3"hg would pass / green

For the Vair... to test engine health...

I plug the Port to the air filter, then put a piece of paper over the oil filler and if it lays flat!

Kevin Wilsson / "UNSAFE" had an exhaust powered "eductor system" that would suck the paper in at idle! He did it for better ring sealing.





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Re: My PCV System
Posted by: DAVECS1 ()
Date: August 08, 2018 06:35AM

Matt, I have used vacuum pumps on forced induction cars with good results. It really seems to keep the engine cleaner and help with ring sealing. less fumy stuff after wide open pulls.

On a normal street engines I have been setting up mild pull through systems like this for many years now. Might be my imagination but it seems to keep the oil cleaner, no condensation on the oil cap, and I don't get the oil mist all over the engine after spinning higher RPMs for an extended amount of time.

I agree with Richard above, there is more than likely positive pressure coming out of the breather. I have to change them every 10K or so on a good engine as the element gets to looking black or oiling in a less than ideal engine. After 6K in the corvair, this one is still white, so that seems like good news, or the end of the fill tube is submerged lol.

1964 Monza Convertible
110 4 speed
Peoria, IL

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