TCKT B8

I was just considering alternate PCV valves for my 65 327 (it's a street rod, not a restoration) and have been unable to find a definitive answer to this question - Are all PCV valves functionally the same? I know there are lots of physically different PCV's, but if you could plumb them into various systems would they function the same? For example would a PCV valve for a 74 Buick function the same on a 327 Chevy or a 400 Pontiac or whatever?

MikeM

Based on similar questions here in the past, I doubt you will get a definitive answer to your question.

There are lot's of different configurations of these valves but there's also several configurations that have different calibrations.

I'd suggest you pick an OEM valve that is used on a OEM engine closest to your engine configuration.

MasterDave

They function the same but have heavier/lighter *****, thus differing vacuum does affect them. Not sure it would ever make a difference in our older engines however. It's all about pollution nowadays.

LB66383

I would tend to disagree to a point. My totally unscientific idea is that a PCV valve is there to allow crankcase vapors to be pulled in and burned under acceleration and other lower vacuum conditions. If you have a "cammed-up" engine with low idle vacuum, the wrong PCV valve will be allowing the engine to suck in vapors at idle. As well as causing poor idle characteristics because of the vacuum leak.

Anyway, I always look for a PCV valve with a light ball or a weak spring for my cammed-up 383 stroker. Something that stays closed until a rather low vacuum level.

mashinter

They are different. When running a carb on the GM flow bench we always ran with the correct PCV for the application. If they were all the same, we could have used just one.

Powershift

I believe that the PCV never fully closes, although it will be almost closed at idle vacuum, and then opening fully under high load (low vacuum) conditions.

Larry

MikeM

I believe that is generally correct but it's what it does in between almost closed and full open is what is different.

The valve may fully close during in gear deceleration. Don't know.

Here is one of the better links I have found on the subject:

https://www.autorepairhelp.us/pcv-va...-and-problems/

Powershift

I took one apart years ago to see what was inside. I THINK that there was a slot cut into the piston or something else that prevented full closure/shutoff...........so that there was always some air/vapor going thru the valve at all times the engine was operating.

Larry

MikeM

Makes sense that it wouldn't totally block all flow even if the pintle closed off the orfice.

I know that on Ford engines of the late '70's/early '80's, you could turn the valve upside down and it would cut off all apparent flow through the valve. The Ford valves looked very similar to the GM valves but as stated, looks can be deceiving.

Dejavet

If your 65 327 is stock, it does not have a PCV valve. It has a "restrictor" valve. I found this out when I tried to build my 65 327 engine to original specs. At the rear base of the carburetor there is a connector for the restrictor valve. From the restrictor valve a hose is run to the oil fill tube which is at the front of the intake manifold. I have always wondered how this can have any control over crank case ventilation. All this valve does is restrict the amount of air that can get through the hose in either direction.

I would like to understand this better because I just changed my plugs and they are very fouled, as always, and the fouling appears to be oil based. I know that a faulty PCV valve can cause this, but what do you do when your PCV is really just a restrictor valve? I have checked the restrictor for blockage, but it is clean.

Has anyone installed a real PCV in a 65 and how do you know you have the right PCV?

Dejavet

MikeM

[QUOTE=Dejavet;1590789411

All this valve does is restrict the amount of air that can get through the hose in either direction.

I know that a faulty PCV valve can cause this, but what do you do when your PCV is really just a restrictor valve?

Has anyone installed a real PCV in a 65 and how do you know you have the right PCV?

Dejavet[/QUOTE]

The fixed restrictor actually limits the amount of vacuum leaking into the engine and pulling out of the crankcase. It's fixed, not variable to suit different requirements like the valve will do.

Some '63 and '65 engines used the restrictor. The same general engines used in '64 used the variable valve. Fuel injection engines of all three years used a PCV.

I can't imagine how a defective PCV valve would MAKE it use oil. I can see how if the PCV system is plumbed wrong, it will ALLOW/MAKE the engine use oil.

TCKT B8

My 65 327 is like yours. The connector for the restrictor valve plumbing is at the rear of the block behind the intake manifold. When I bought the car it had a PCV valve in that line hooked to the port on the back of a Holley double pumper. That didn't look very stock.

I have not found a replacement part for a "restrictor valve" anywhere so I've switched to an Edelbrock carb with a PCV port on the front of the carb. I'm thinking I can run a hose from the restrictor valve connector to a connector on the Edelbrock air filter housing and then place a PCV valve in a hose between the port on the front of the carb and the port on the side of the oil filler tube. I plan to use a closed cap oil filler tube with a hose connector on the side instead of the stock 65 filler tube with a vented cap.
That's why I'm trying to find out if all PCV valves are the same (to find one that will fit in the line from the carb to the port on the oil filler neck). Anyone have any thoughts on that setup?

Dejavet

Mike, It sounds like you know much more about early Corvette engines than I do. Maybe you can explain why my 350 horse 327 came with the restrictor and not a PCV? It sounds like the stock configuration just does not have any positive crankcase ventilation?

I did not mean to say that the PCV caused the oil fouling on my plugs. I am not knowledgable enough to make that statement. I did research the causes and the PCV valve came up often as a possibility. I decided to pursue that possibility because it seemed to be easy. Am I wasting my time?

Charlie

MikeM

ALL new cars sold in the US after 1962 had a POSITIVE crankcase ventilation system. '61-'62 California cars used an OPEN ventilation system. The two systems are described in the link I posted.

https://www.paragoncorvette.com/corv...atalog/c2/#4/z

PS. I may have erred above when I said '64 carb engines used valves instead of restrictor. No matter. Doesn't matter. You can scroll to a system similar to yours. Sounds like your engine isn't really OEM configuration though. Also refer to '66-'67 which sounds closer to what you have.

MikeM

I think you need to post a picture of your system. If you think your crankcase ventilation system is causing your engine to use oil, it could be in the plumbing and nothing to do with a restricter or valve either one.

Dejavet

Mike,
My configuration is exactly as pictured in the lower left corner of the page. It is labeled 350 - 365 horse. The restrictor valve is item number 35. My configuration is stock, but the engine has been modified. I have read the theory behind the PCV valve and I just don't see how a restrictor valve does the job of a PCV valve.

Dejavet

Dejavet

I am no authority on this subject, but I have the same questions you have and in my research I have determined that there are many different PCV valves. I don't know how you would determine which would be best for your application, but I did find an "adjustable" PVC. It is made by Wagner Performance. I would assume it comes with instructions on how to adjust for your application. I am sure you could find it with a Google search.

Dejavet

Powershift

The carb is factory calibrated and jetted based on PCV valve specifications and performance (among other things). I would guess each car manufacturer decides what is best for his particular engine based on design and dyno studies.

I would simply buy one that is closest to your engine year and configuration, install it, see how it functions, and then adjust the carb jet and rods etc as needed based on spark plug readings.

For you car I would start with one for 1965-67 period for the 327 engine (regardless of HP) and then follow my recommendation above. If you go to far out (1970's period) the PCV design may be a bit different due to emissions issues and constraints.


Larry

MikeM

If you insist on a valve instead of a restrictor, refer to the '66-'67 illustration as I mentioned. Use the '66-'67 oil filler pipe with the bung that allows a screw in PCV valve. Run a hose from that valve to the carb (not throuh the existing restrictor) and you're done!

The thought behind the 1960's technology for crankcase ventilation is to keep a constant negative pressure with air flow on the crankcase. The restrictor is one way to do it. The valve is another. The difference is the valve is variable flow and the restrictor fitting isn't. The valve does a better, controlled job with the same objective.

I don't understand the problem here I guess.

cardo0

TCKT B8 i think the best advice here is what has been stated in choosing an OEM PCV vlv that is for an engine that closely matches your engine configuration. It may even be a big block PCV if your engine is non stock.

As for the PCV installation something that might help is to make a drawing showing the flow path from a clean air source through the crankcase/block and then through the PCV vlv and exits into the intake (usually under the carb).

Something thats not to expensive and used to tune your carb with any PCV vlv is an "Wide Band" O2 monitor. Without cat converters u can just stick the sensor up the exh pipe (hold it there w/clamp) and mount the gauge temporarily to tune the carb. No matter what PCV vlv u use the wide band dosent lie and will show whether your carb is lean or rich. Back in 60's they didnt have cheap wide band monitors but now u can buy a quality WB monitor for under $300.

Something to consider.