The Stovebolt Site Forums The Shop Area Engine Shop Testing PCV Valves

So I am trying to figure out the optimal PCV valve to use for our 216/235/261 engines. There is a significant difference in them. To test, seal up the valve cover cap hole, test with a vac gauge through the dipstick tube.

The V-237 Valve reads about 2 inches on the vac gauge.
The V-178 Valve reads about 5 inches on the vac gauge.
The V-112 Valve reads about 10 inches on the vac gauge.

According to http://www.aa1car.com/library/pcv.htm it says the optimal reading is 1-3 inches. So, my testing shows that if that article is accurate, the V-237 is the best choice.

So do you experts out there feel this is valid? Is 2 inches sufficient to evacuate the exhaust gases?

The article I have shows 1-3 inches of Mercury(vacuum).

I am excited about this because its one of two excuses I gave my wife as to why I needed a test engine.

The results are in, and I finally have a more scientific means of testing to see exactly which PCV Valve is optimal for our specific engines.

The V-237 wins! All of the test data and pics are here:

http://devestechnet.com/Home/PCVInstall

you sir are a god. I was wondering the same thing last week about if the one im currently using is the correct one.

It stands to reason that if I am curious about something, someone else may be too. I am below average when it comes to mechanical expertise. I just have good friends who share their knowledge. Pass it on!

I have a feeling mine is letting too much vacuum thru. I'm going to confirm what one I'm using and switch accordingly

An inliner expert told me to get a pcv valve for a 250ci inline Chev. Have the set up on a couple engines works great.

An inliner expert told me to get a pcv valve for a 250ci inline Chev. Have the set up on a couple engines works great. Trimmed the open downward pointing, tube off the draft tube welded in a plate and drilled and tapped a hole for an elbow fitting, have pcv pointing upward.

Thats a V-184 so that would be about 4 inches when the target is between 1 and 3 optimally. The V-178 I used for years was 5, so I am sure you are happy with it. I am only recommending the V-237 because its THE target of 2 inches. I wasn't satisfied with wondering, so I tested to be sure.

How well does it work at full throttle and max load on the engine? That's where it needs to be tested.
Jerry

I heard of a large displacement Chevy engine PCV put in a small Chevy engine in small cars as the Vega and it allowed too much air flow.

Which caused the oil to get sucked out of the crankcase.

That is a good point Jerry. But no I still ain't buyin your Dyno! ;)

Here is the way that Sam Bell from Motor's Testing Facility put it...

As you might expect, blowby gases are produced in varying amounts under different operating conditions. At idle, when manifold vacuum levels are high and loads are low, crankcase fumes are at a relative minimum. Under these conditions, the high vacuum sucks the restrictor to nearly close the valve. Makeup air is supplied to the crankcase via the filtered breather cap, or breather hose, “positively” displacing the crankcase fumes.

Under midrange throttle openings, engine loads and speeds are higher, and more blowby gases are produced. Manifold vacuum, however, is lower, so the spring tension can largely counterbalance the pressure differential, thus allowing increased flow through the valve. As before, the breather supplies clean air to displace the fumes.

At very high throttle openings, intake manifold vacuum drops to near zero. Spring tension then holds the valve open for maximum flow, just as it does with the engine off. Even so, the amount of blowby gases needing evacuation often exceeds the flow capacity under high-load conditions. At such times, a substantial portion of crankcase gases may flow backwards from the engine through the breather and into the air filter housing. (This accounts for all those oily breather filter elements we changed back in the not-so-good old days of carburetion.)

---- Since we are talking about the good old days of carburetion, the engine shops advice, as well as various web sites out there, not to mention a few of our own StoveBolters, have suggested that 1 to 3 inches of mercury at a stable Idle will be the best compromise and is the accepted industry standard.

To further complicate matters, these engines weren't designed for PCV and the engineers felt that a 1-1/4" HOLE was sufficient! Since the PCV Valves I am using have the industry standard size, we can assume the manufacturers through what they call flow testing, can make a positive vac pull on a 3/4" hole. 1 to 3 inches at a stable idle accomplishes this. Of the 20 or so inches present in manifold vac pressure, this Valve pulls 2 (or about 10%).

To answer your question Jerry... I rely on other experts so I have to go with JUST FINE.

"X"- - - -Unknown quantity used in math calculations.

"Spurt"- - - -a drip of water under pressure.

"Expert"- - - -an unknown drip under pressure. Good luck with that.

Road draft tubes provided negative pressure in the crankcase at speeds above 30 MPH due to the venturi effect of air flowing past the end of the angle-cut tube sticking down into the airstream under the vehicle. It worked 70 years ago, and it still works today.
Jerry

Yet in other peoples post YOU were touting the greatness of PCV and how much better it is than what they had back then!

Don't you hate it when the words don't come out of MY mouth and you have to disprove real-life actual experts in the field?

Meanwhile, I think my work is done here. On to HEI!

The king of copy and paste strikes again! Ever had an original thought?

Jerry

While I never like to get into the middle of a good whizzing contest (I am lying. I just make sure that I stay out of the way of the crossing streams!),
HRL hit the nail on the head, especially with these old blow-by prone engines. You need maximum crankcase evacuation at mid to full throttle. The downdraft tube provides that, while the PCV system does not.
This commode-like post has enlightened me about where the schmutz, which accumulates on that small maxi-pad inside of the air cleaner (newer vehicles than ours) comes from. I could never grasp why it would collect there given that the flow was supposed to go the other way. Now we know. Thank you "King"
Carl

Carl if you read Sams post, you DO get max evacuation at mid to full throttle. It all works exactly the same as the 250 and beyond engines.

My theory is, the reason for all the blowby proneness is slits in the valve cover opening your engine to all sorts of road sand and crud being sucked in, no crankcase gas evacuation thus soot and gas-crud mixing with your oil, causing the upper end to get plugged up prematurely, and top it off with a filter system that filters less than 18% of the oil! All preventable every bit as well as engines much newer.

I realize the road draft tubes design is such that it pulls air out of the crankcase using the venturi principle (still positive), not push air in, but it's very inefficient by today's standards. Its MUCH dirtier but if you are stock aficionado, it works! No need to fix what you perceive isn't broke. The KANG has left the building! Thank You, Thank You Very Much!

With respect to the open road draft tube, the process would be better (more generally) known as (and described as) the Bernoulli Principle/Effect?

https://en.wikipedia.org/wiki/Venturi_effect

Nope. Different Italian! But.. Looks like they DID know each other...

The Bernoulli Principle and its corollary, the Venturi effect, are essential to aerodynamic as well as hydrodynamic design concepts.

There is no check valve so air flow could go in either direction.

The "maxi pad" was able to get coated from vapors making them wet as the vapors condensed.

Being wet and they were exposed to unfiltered air the dirt stuck to them.

The PCV has a calibrated orifice so even when the spring tension can not be over come there is still crankcase ventilation. No matter what engine speed or road speed is. Plus there is no downdraft tube to drip oil on the driveway or garage floor.

Downdraft tube has no positive airflow without the car moving for no pressure differential will be created.

Then do not forget whether PCV or Downdraft Tube the engine still has a breather cap so there will not be excessive pressure built up.

Even my 1935 Buick had a louvered vent on the rear side of the valve cover.

Gm makes a pcv with a small pin hole in it to allow constant ventilation.

What about a system that uses the best of both approaches? It sounds to me the downdraft tube might be preferable at speeds over 30 mph or so. It sounds to me the PCV system might be preferable at idle and at speeds up to 30 or so. The crankcase needs a slightly negative pressure to help discourage oil leaks as well as to evacuate blow-by. Surely we have enough brain power to solve both challenges here, yes?
Jon

Jon, the tree huggers would break out in a terminal case of hives if we let even one cubic inch of oil vapor out into the atmosphere! Stuff that's been buried underground for thousands of years suddenly becomes as deadly as Ebola once it goes through an engine!

Maybe they could do their part in reducing the CO2 problem by holding their breath for about 30 minutes!
Jerry

Agree. Actually Jon, its not necessary because if you read Sams explanation earlier in this thread, its resolved. The same PCV system that works on all engines to date is just fine for our purposes and then some. The only issue was WHICH PCV Valve. The road draft tube was a good start when GM was just in its infancy, but the PCV system is so good that all auto manufacturers adopted it. And, a breather cap, a freeze plug, a grommet, 4 feet of 3/8 fuel/PCV line, a fitting for your intake manifold and a valve will run you about $30. Then, at ALL speeds you are no longer contaminating your oil with crankcase gases. You will be a gazillionaire if you figure out anything better.

Maybe they should break out into a terminal case of hives or some other terminal something. I like the idea of a slightly negative atmosphere in the crankcase and I like the idea of having that condition at all speeds...
Jon

Deve,
I like the idea of the PCV valve and I greatly appreciate all the work you put into finding the correct one. I have read the article on your website and I have a question. I have a 216 in my 1950 Chevy truck, that valve cover has slots on the top of it, I assume for air entrance for the draft tube to work, these would need to be closed off. Would you have a recommendation on best way to accomplish this. I thought about a bead of gasket sealer or JB weld.

I would love to hear what others do for that. I can see both ideas would work. I also like to see people doing those kinds of modifications where they can be undone to restore to original. They make metal tape that could work, but you want something that can't possibly fall into the rocker assembly and cause damage. If you are a welder, you could put a piece of tin over the hole on the inside, then weld it shut. If you are careful, it would be easily reversible. I hope others chime in!

Will the 235 engine generate enough vacuum to run wipers as well as the PCV from the intake port?

Yes, set up a few that way.

I tell people to be aware that it may have an adverse effect on the wipers. It's not very scientific, but neither are the wipers. They really need all the vac you can get and even then you should carry a can of RainX with you. Personally, I go with electric wipers because I have a bad attitude about vac wipers.

The V-237 PCV Valve that has been tested to work best takes 2 inches of mercury out of about 17-20 available. There is no good way to answer that question other than depends.

The famous bad habit of vacuum wipers (used by Ford after everyone else learned): it's raining, you accelerate to pass a slower car, vacuum drops from perhaps 10-15" to 5", and the wipers stall in mid-swipe, leaving you blind until you let off the gas.

What a PCV does not do is dispose of high crankcase pressure:
1. it was never supposed to.
2. it's caused by bad ring seal, not a badly engineered system.
3. if you try to seal all the outlets it will blow out the dipstick, valve cover gaskets, pan gasket, etc. and spray oil vapor all over the engine. If you're lucky, it won't land on the exhaust manifold and burn the car down.
4. adding "breathers" to the valve cover: read 3. above.
5. the best you can do (other than new rings) is a large diameter duct (to keep the vapor speed as low as possible) from a source (valve cover, timing cover, pan, valley) into a labyrinth with baffles that prevent the oil from escaping, and release only (relatively clean) hot vapor.