[mklinger]

It's been discussed a lot throughout the years of the importance of properly ventilating one's crankcase. I agree that the pontiac engineers had it correct by I have discovered that this is not easy to replicate without some effort if your build is not 'factory'. By effort I mean that you can not rely on the the off the shelf replacement and aftermarket parts doing what they were supposed to do 50 years ago. So here's the story.

When I built my last engine I needed a PCV valve. I went to my trusty auto parts store, gave them the vehicle and they gave me the part that was called for. This PCV valve was stamped '2020' on the body. Installed it and away I went.

Now I know I need breathers so I purchased (2) valve cover breather that looked like they would do the job and because I didn't want oil all over the valve covers since I was not running back to the air cleaner like the factory did I purchased baffled grommets. Installed it and didn't look back.

Engine runs great but I have this annoying drip out of the rear main. I am damn sure that the seal was installed properly so after some thought I decide to backtrack through the components related to the crankcase ventilation and here's what I find.

1. Maybe it's the PCV valve.

I check the original part numbers from Pontiac and they call out a 'CV-697C' and if you cross reference that you will wind up with a part that looks like the one I have stamped '2020'. On a lark, I go on Ebay and purchase a vintage CV-697C for about 15 bucks.

Here's what I found. Look at the difference in the size of the pintles. Vintage CV-697C on the left vs. the 'one size fits most' 2020 on the right.



Tom Vaught on here has said that a properly sized PCV valve should flow about 4 CFM and I would assume the factory original did. I doubt the current replacement part does the job. Buy yourself the right part, the vintage CV-697C. There are plenty on Ebay.

2. Maybe it's the breathers.

So I pull the breathers and just to test that they flow air I blow through them. Slightly restricted because there is some foam in them but they seem OK. Then I pull the baffled grommets and blow through them. I am able to blow next to nothing through them due to their design, a hairline slit between the upper and lower baffle. For grins I insert the breather into the baffle and blow again. Now, absolutely nothing. The bottom of the breather is applying pressue to the baffle so it can not flow at all. This engine is not breathing.

3. Maybe it's everything and I just got it completely wrong the first time.

At this point the PCV valve is replaced with the correct CV-679C part. Because I was using aftermarket aluminum valve covers, the factory tube to the aircleaner on the passenger side was not an option as was the oil filler on the drivers side. My current path is -10AN fittings and hose to the filtered side of the air cleaner with no restrictions from both valve covers. I suspect with this configuration the PCV will suck and the crankcase will breath and any positive pressure that may have been causing my rear main to weep will be in the rear view.

What did I learn? Don't just install the parts, make sure they are doing the job you and some engineer 50 years ago expected them to do.

Just sharing my recent experience. Hope this helps someone.

[Dick Boneske]

I think you have a rear main seal leak. I doubt if it has anything to do with the PCV system. I've had very few stock Pontiacs that do not drip from the rear main.

[JLMounce]

I too think that you probably just have a leak. The PCV may have been working okay.

Real crank case vent issues crop up in things like pushing oil out of the dip stick and ending your weekend cruise with an oil slick under the car or pushing oil past your control rings and producing blue smoke. Ask me how I know. I used a PCV supplied by Butler with the tomahawk valley pan I use. For around town everything was fine and functioned as you would expect. As soon as I started taking the car on long highway drives, that's when issues started to crop up for me. With somewhat steep gearing, short overall tire height and no overdrive, I would easily sustain 3000+rpm for maybe an hour or more at a time. This high rpm, high vacuum situation caused all manner of issues with my 455. On a trip to Bandimere speedway (75 miles) it pushed out enough oil from the dipstick to coat almost the entire barrel of the front passenger wheel. On the drive home, it wrecked what was left of the oil seals in the engine. The next morning I had well over a quart of oil on the garage floor.

If that's not happening, more than likely your PCV system was at least working for the type of driving you're doing.

I worked with Mighty Mouse Solutions to design a crank case ventiliation system adequate for my driving type and engine power. I ended up with their draft can/oil separator plumbed directly to the valley pan, bypassing a PCV valve all together. I recycle crank case gasses back to the combustion chamber, after separating oil and fresh air vents in to the engine via a single breather. It's worked incredibly well so far and in a year's time of driving the catch can accumulated about a teaspoon of oil is all.

[Schurkey]

Originally Posted by JLMounce

I too think that you probably just have a leak. The PCV may have been working okay.

Not if there's no air flow through the "baffled" grommets.

Originally Posted by JLMounce

I ended up with their draft can/oil separator plumbed directly to the valley pan, bypassing a PCV valve all together. I recycle crank case gasses back to the combustion chamber, after separating oil and fresh air vents in to the engine via a single breather. It's worked incredibly well so far and in a year's time of driving the catch can accumulated about a teaspoon of oil is all.

Photo(s)?

Kinda guessing this system brings crankcase fumes to the air cleaner (carb vacuum) rather than the intake manifold (manifold vacuum).

If this directs fumes to manifold vacuum, I suppose it relies on a restrictor orifice like some of the LS engines are using in lieu of a PCV valve.

[wakesupremo]

i have a valley pan that doesn't have an outlet for a PCV. Could I install one in the fuel pump blank off plate?

[Kenth]

Originally Posted by wakesupremo

i have a valley pan that doesn't have an outlet for a PCV. Could I install one in the fuel pump blank off plate?

It would be easier to install the PCV valve in drivers side valve cover, like the way it is on 1973-74 455 S.D.

JMHO

[mklinger]

Referring back to my opening post, yes I have an oil leak and I inferred that my changes to the crankcase ventilation set up 'may' abate the chronic drip.
But, the meat of the story was that the leak caused my to review the PCV valve and the breather set up which was for the most part, ineffective.

The PCV valve was clearly undersized for the motor and the system had no source of fresh air intake for the PCV when it was under vacuum
If the system went to any positive pressure, there was nowhere for the pressure to go, except 'maybe' out the rear seal...TBD.
This was because the breathers were essentially caps in the valve covers due to the baffle design preventing the engine to breath under either pressure or vacuum.

Regarding my leak, the outcome remains to be seen as I am still waiting for parts to complete my PCV redeux. I will report back my findings in that regard in the future.
I am confident I will have a properly working crankcase ventilation setup shortly..

[JLMounce]

Originally Posted by Schurkey

Not if there's no air flow through the "baffled" grommets.


Photo(s)?

Kinda guessing this system brings crankcase fumes to the air cleaner (carb vacuum) rather than the intake manifold (manifold vacuum).

If this directs fumes to manifold vacuum, I suppose it relies on a restrictor orifice like some of the LS engines are using in lieu of a PCV valve.

You do commonly see this setup on modern muscle cars, LS's, Hemi's etc. ecxept for the air/oil seperator, there's not restrictor occurring here. There is an open grommet in the valley pan with a barbed fitting to -8 AN hose connector. This is routed to the draft can, oil is separated there, then recycled to the back of the manifold.

The draft can is closed, so I'm recirculating blow by gasses until there is pressure at which points it will vent the system.

https://www.mightymousesolutions.com...page/draft-can

According to mighty mouse, without the PCV valve installed, this provides enough crank case pressure relieve up to around 800hp. I'm nowhere near that power level, but due to my engine sitting for about 15 years before I got the car on the road, it's ring seal isn't that great and does produce a bit more blow-by.

[mklinger]

JL, so I understand. You have no PCV valve so the flow is unrestricted to the can and then to the intake manifold. I do see a breather on the drivers side. Is that unrestricted as well? Also, how do you think your setup would play with A/F ratios with EFI? I know you have spent a lot of time with Fitech which I also have.

[JLMounce]

Originally Posted by mklinger

JL, so I understand. You have no PCV valve so the flow is unrestricted to the can and then to the intake manifold. I do see a breather on the drivers side. Is that unrestricted as well? Also, how do you think your setup would play with A/F ratios with EFI? I know you have spent a lot of time with Fitech which I also have.

That's correct, it's functioning like a PCV valve where you're moving pressure from the crank case to the intake, until there is a surplus of pressure and at that point the draft can will vent the pressure.

The breather has some foam in it to keep oil contained, but is otherwise open.

I did not have to change anything in my tune when I made this change and have not witnessed any changes in my reported AFR's or my short/long term learn trims.

The big thing this is doing for me is providing ventilation operation during high vacuum/high rpm situations where a stock type PCV valve would otherwise be closed.

[Goatracer1]

Under High vacuum the PCV is OPEN not closed no matter the rpm.

[Tom Vaught]

THE ONLY TIME THE FACTORY PCV VALVE IS "CLOSED" IS:
IF THE ENGINE HAS A BACKFIRE.

You do not want a flame to enter the oil pan area and light off the oil vapors.

Tom V.

[JLMounce]

Originally Posted by Goatracer1

Under High vacuum the PCV is OPEN not closed no matter the rpm.

Yes it’s not really ever completely closed, unless as Tom states it is under backfire, but under high vacuum it flows the least.

https://help.summitracing.com/app/an...cv-valve-do%3F

This is why at higher rpm cruise where vacuum and rpm is high, I had issues and why I went to a draft can in my situation.

[chrisp]

Originally Posted by JLMounce

That's correct, it's functioning like a PCV valve where you're moving pressure from the crank case to the intake, until there is a surplus of pressure and at that point the draft can will vent the pressure.

The breather has some foam in it to keep oil contained, but is otherwise open.

I did not have to change anything in my tune when I made this change and have not witnessed any changes in my reported AFR's or my short/long term learn trims.

The big thing this is doing for me is providing ventilation operation during high vacuum/high rpm situations where a stock type PCV valve would otherwise be closed.

Any increase in engine vacuum @ idle after the upgrade ?

[JLMounce]

Originally Posted by chrisp

Any increase in engine vacuum @ idle after the upgrade ?

Not from the change to the draft setup. What helped me the most in that regard is letting the EFI control the timing. Gained a full 2” of vacuum at idle with the ability to command up to 24* of advance at idle. The system idle stabilizes advance between 18-23 degrees usually.

[Skip Fix]

"You do not want a flame to enter the oil pan area and light off the oil vapors."

In college my best friend back home had an L-88 67 Vette. He had over heated it and had burned a small hole in a piston unknown to him.I came home one weekend and we were going to take it out to "cruise" Forest Lane in Dallas. Blew the valve cover on one side off the bolts!

[Goatracer1]

Many years ago I had a 1963 Chevy pu powered by a 400 Pontiac as a daily driver. One winter day the temp was so cold it wouldn't start so I gave it 2 blasts of starting fluid (ether). After the 2nd blast the engine backfired and split the M/T aluminum valve covers wide open sending 1 of the breathers sailing by my head. The explosion blew the valley cover off over the bolts and blew the oil pan down a 1/4 inch all around the block. Last time I ever used ether .

[wakesupremo]

Can somebody please explain in 'laymans terms' The reason for the PCV. I know that it relieves crank case pressure but, my engine builder, who has done a great job on my 469 build, is adamant that I don't need a PCV as I have a breather in both valve covers open to atmosphere. However, I do have little oil leaks that are non explainable. He is a ford racing engine builder normally but, as we have been told many times that nobody in UK can build a cecent pontiac engine, he had a go!!! Most people on here say that it is necessary. Can somebody explain please.

[Kenth]

Stay away from "racing engine builders". That is if you´re not driving around with the loud pedal to the floor 100% of the time. Like racing on a track and changing engine oil once a week.

A functional pcv system keeps the inside of the engine freer from combustion residues and condensation and the environment cleaner. From 1966 and 1968 service manuals here below.

[Schurkey]

A "vented" engine using only "breathers" must, by definition, have higher pressure in the crankcase than atmospheric pressure, or there's no way the fumes can push through the "breather" filter element(s).

An engine with PCV (Positive Crankcase Ventilation) has fresh air drawn into the crankcase by (regulated) manifold vacuum. The crankcase stays "cleaner" with PCV than with silly "breather(s)", and has essentially atmospheric pressure inside, not above-atmospheric pressure.

On a "closed" PCV system, even if there's more crankcase fumes than the PCV valve can remove, (heavy blowby/low vacuum) the excess fumes are vented into the air cleaner area, so that whether the fumes come through the PCV valve or back-up through the air cleaner, they're still routed back to the combustion chambers and happily disposed-of.

Any engine run primarily at part-throttle should have a proper, functioning PCV system.

A "race" engine, that operates primarily at heavy-throttle, may or may not benefit from PCV.