Pcv

[meadowbrook]

Just received a Pcv kit from vpw and I am puzzled by the valve which has an arrow pointing to the manifold side.

In that direction, it freely flows air through it. I was under the impression that this needed to be an orificed type flow otherwise I'd get a large vacuum leak, no?

If I blow air the other way (from the manifold to the crankcase, the valve shuts .

Is this correct?

[48mirage]

"Is this correct?"           Yes

Edited October 16, 2014 by 48mirage

[JBNeal]

here's an example of a similar setup 

[DonaldSmith]

I think that the PCV valve reduces the manifold vacuum as a matter of course.  Of course, I could be wrong.   Maybe that's why my vacuum gauge reads low. 

 

The Positive Crankcase Ventilation  system pulls crankcase fumes into the intake manifold for burning in the engine, rather than spewing the fumes into the atmosphere.  This pulls in some extra air.  

 

The one-way valve is to prevent backfires from getting into the crankcase.   That's my story and I'm sticking to it. 

[meadowbrook]

Thanks. It just seems that from my research, at idle with high vacuum, the valve should be more restrictive than this one

[meadowbrook]

So last question, since iam introducing a large vacuum leak, should i use a larger idle jet?

[Reg Evans]

I am just curious here. Why do you want this PCV system ? Do you have a lot of blow by er what?

[DonaldSmith]

For my part, I put my PCV system in because I could, and, although I'm not a tree hugger, I felt good about eliminating some of the pollution these cars put out.  

 

We still have the non-catalyzed, unburnt hydrocarbon exhaust, for nostalgia's sake.  Particularly for the Woodward DreamCruise, I have modified a line from Apocalypse Now...  "I love the smell of exhaust in the evening". 

[meadowbrook]

Well, I want the pcv because of the stink of crankcase fumes that sometimes gets to the interior and stinks up the garage. Plus it's better for the engine anyway.

[Reg Evans]

OK....I understand the STINK part but what do mean by saying ......" plus it's better for the engine anyway"?

[meadowbrook]

Well, it does a better job in clearing out condensation from the crankcase that the draft tube does, but really, even if that's not necessarily true, it is the stink that is the biggest driver.

Can't be good to breathe that crap.

[TodFitch]

OK....I understand the STINK part but what do mean by saying ......" plus it's better for the engine anyway"?

First PCV (positive crankcase ventilation) systems were on some very high end cars in the late 1920s. Basically mainstream Detroit ignored it as they deemed the road draft ventilation as "good enough" and a lot cheaper to make. Exception being for military as they wanted to be able to ford fairly deep water where the draft tube would be a problem.

 

Later, it was found that the vast majority of automotive based air pollution from an "uncontrolled" engine was actually from the crankcase not the exhaust. Solution was to use the 1920s invention and you get a twofer: Less pollution and longer engine life. Only down side being a few cents more in the manufacturing.

 

I've been amused/annoyed by people who think that PCV stands for "pollution control valve" and immediately decide it has to be removed. A fellow I once knew just sealed it up. He couldn't understand why he kept having bad seals and leaks. A pressurized crankcase will do that.

 

You have to have some ventilation. The question is will it work at all speeds and where does the stuff go when it leaves the engine. With a draft tube, it only works at speed, maybe 30 MPH or so depending on design. And the crankcase fumes which contain unburned hydrocarbons, does into the atmosphere. With a PCV system it should vent properly at all times with the possible exception of full throttle acceleration and the unburned hydrocarbons go into the engine to be burned.

[JBNeal]

Since I installed that test setup, not only is the stink gone, but so is that oil drip from where the draft tube was.  My perception is that the truck starts better now and that the oil is a little cleaner, but I never established a baseline for these so I cannot say for sure how much improvement has been made.  I do know that on a few startups where I did not choke-throttle appropriately and there was a small backfire, I did here a -CLICK- that I had never heard before whenever I goofed up this way.  I am assuming that was the PCV valve slamming shut, so at least that works 

[Guest gdaddypaul]

Under what circumstances would the road draft "leak" when my truck was being cranked up onto a rollback after stalling out and refusing to restart? Also, there was what appeared to be transmission oil dripping from the underside, onto the flatbed once my truck was loaded up. Does the tranny have a vent, also, that doesn't like being on a 45 degree angle?

[DJ194950]

Check your oil level and consistency Possible fuel pump when bad and was putting fuel in the crankcase.

No fuel to carb.

Overfilled crankcase due to gas in it leaked the excess fluid out the road draft tube when tilted on the rollback.?

 

Trans leak, bad output shaft seal that normally only leaked slightly allowed oil to leak more on the tilted bed??

 

A couple of thoughts.

 

DJ

[Guest gdaddypaul]

Thanks DJ194950

[The Oil Soup]

Wouldn't it be better to plumb the crankcase gas upstream of the carburetor?

[TodFitch]

Wouldn't it be better to plumb the crankcase gas upstream of the carburetor?

You want a low pressure (vacuum) to pull clean air through the crankcase. Upstream of the carburetor you are at atmospheric pressure so while you will relieve a high pressure situation in the crankcase you won't be moving air through it.

[JBNeal]

my setup is only half complete per the original PCV factory setup right now, but that may change soon.  The air cleaner modification allows excess vapors to be drawn out of the crankcase through the oil filler pipe