PCV or not?

[not so famous bob]

View attachment 557446

Here's a simple picture of how it works.

1968 hemi`s came this way , u figure !!
I run a pcv on the drivers side , and a breather on the pass. side, but, I have a sealed 6 pack scoop, works fine .

 

[miller]

Does the pcv have any purpose except environment reason?

Just re-read through it all. Started driving in California, so assumed it was EPA.

Anyway, past my lame excuse, if your really concerned about the air going into your intake, just make sure you have breathers (vents) on each valve cover.
Don't know where you live, but state to state requires it, if it's original equipment.

You really even need a catch can? Shouldn't.

 

[383man]

I know how the PCV works, but not a single one have told me why I need to put crappy air in to my engine, and if that question is below your intelligence.....don´t read it!

You have been told by about 6 people on this thread why a PCV is good on a street car and just how it works. If you cant understand that then its no sense in telling you again so you should not insult the intelligence of people trying to help you who do understand why its good for a street car. Ron

 

[Steve Garner]

Cute...my intelligence says...blame the EPA!
Before the PVC systems were introduced, piston engines used a simple open tube vent, that attached on a valve cover, going to the bottom rear of the engine. Idea was simple, since any piston engine MUST be vented, to avoid creating a vacuum inside.

No, that's not quite right either. The vent tube you are referring to was called a "road draft tube" and it's design was such that when the vehicle was in motion the air moving past the end of the tube created a vacuum in the tube, not at all unlike what a pcv valve does, drawing the vapour out of the crankcase. Very little is unburnt fuel, it is mostly water and chemical vapours created in the crankcase. Simply venting only relieves the pressure that would build, it does not extract the harmful (to the engine) vapour that lingers in the crankcase. That's why just vents on the valve covers are woefully inadequate.

The problem with road draft tubes was two fold. One, it vented the vapour to atmosphere, but secondly, and equally important, they didn't work unless there was sufficient vehicle motion to create the low pressure in the tube. So they didn't work in stop and go traffic. All they were doing in those circumstances was venting any pressure, but not removing the vapour.

So to the poster's question as to why you would want to put that contaminated air down the throat of your carb and burn it? Because it is the cleanest way to dispose of them and because the effects on performance, given the small percentage of intake air it makes up and the composition of what it's carrying (mostly combustible hydro carbons) , are so small as to be barely measureable.

 

[Lelo 500]

I know how the PCV works, but not a single one have told me why I need to put crappy air in to my engine, and if that question is below your intelligence.....don´t read it!

Yep..... We're stupid..... You should run it like you have it.

 

[miller]

Time for a beer...

So they didn't work in stop and go traffic.

I've seen enough in my lifetime, sitting and idling, and smoking out that tube.

 

[Lelo 500]

It's Miller time!

 

[janbanan]

I surrender!

 

[HEMI-ITIS]

Just use a vacume pump into an overflow devise with a breather.

 

[oldbee]

No, that's not quite right either. The vent tube you are referring to was called a "road draft tube" and it's design was such that when the vehicle was in motion the air moving past the end of the tube created a vacuum in the tube, not at all unlike what a pcv valve does, drawing the vapour out of the crankcase. Very little is unburnt fuel, it is mostly water and chemical vapours created in the crankcase. Simply venting only relieves the pressure that would build, it does not extract the harmful (to the engine) vapour that lingers in the crankcase. That's why just vents on the valve covers are woefully inadequate.

The problem with road draft tubes was two fold. One, it vented the vapour to atmosphere, but secondly, and equally important, they didn't work unless there was sufficient vehicle motion to create the low pressure in the tube. So they didn't work in stop and go traffic. All they were doing in those circumstances was venting any pressure, but not removing the vapour.

So to the poster's question as to why you would want to put that contaminated air down the throat of your carb and burn it? Because it is the cleanest way to dispose of them and because the effects on performance, given the small percentage of intake air it makes up and the composition of what it's carrying (mostly combustible hydro carbons) , are so small as to be barely measureable.

This is the “nitty-gritty”. Steve nailed it IMHO.

 

[lewtot184]

Several people seem to have questions about the catch cans, including me. Could someone explain, and maybe post a picture? I tried a PCV on my car. Seemed fine until I fired it up one time, and got a big cloud of blue smoke out the exhaust. I plugged the PCV, and no more smoke. It was hooked to the back of the carb. No place in front. I think there's something wrong with how i did it, so i might need a catch can. If it were explained better.

youn may not have a baffle in the valve cover under the pcv.

 

[coloradodave]

This thread could have stopped at post #15...

 

[mopar 3 B]

Yea, sorry I should have mentioned that you would remove the hose to the air cleaner. The rest of it makes sense.

Just think about it, when the engine is in vacuum(IE: off throttle) your engine is pulling air in. When you floor it and the engine goes to zero vacuum your drawing the PCV valve open and now the engine is passing all the built up pressure(and oil blow by) through the carb and burning it through the cylinders. So therefore you have no blow by.

Wrong. Wrong. Wrong. PCV only pulls at high vacuum. High vacuum is not at WOT. Also the crankcase is not a vacuum pump.

 

[mopar 3 B]

This post could have stopped at #15...

This post will stop at any state dnv that requires an emissions inspection. It will not pass without one regardless of how plumbed.

 

[Steve Garner]

Time for a beer...


I've seen enough in my lifetime, sitting and idling, and smoking out that tube.

Yes, the tube will vent excess pressure. But what is pushing that vapour out the tube is the newly created vapour. More toxic vapour pushing out toxic vapour. There is no flow of clean air into the crankcase so you have a crankcase constantly filled with nasty vapour. That's the flaw with draft tubes. In this case, they don't suck.
What you want to happen is the suction on the tube, or hose in the case of the pcv, to be flowing a greater volume of air than the vapour being created. You create a negative pressure in the crankcase. So what that does is pulls clean dry air into the crankcase from the inlet vent. That's why the oil filler caps that were used along with the road draft tubes were open and stuffed with steel wool. Allow fresh clean air in to replace the nasty vapour being pulled out. This is what keeps the acids and vapours from condensing inside the engine.

When the engine wears to the point that the blowby is putting more vapour into the crankcase than the draft tube or pcv can flow, it backs up through the intake part of the vent and oils up the air cleaners in the ones that draw their replacement air through the air cleaner.

 

[mopar 3 B]

Forget it he is not going to get it anyway. So let him put a puke can on it if it makes him feel better.

 

[janbanan]

Yes, the tube will vent excess pressure. But what is pushing that vapour out the tube is the newly created vapour. More toxic vapour pushing out toxic vapour. There is no flow of clean air into the crankcase so you have a crankcase constantly filled with nasty vapour. That's the flaw with draft tubes. In this case, they don't suck.
What you want to happen is the suction on the tube, or hose in the case of the pcv, to be flowing a greater volume of air than the vapour being created. You create a negative pressure in the crankcase. So what that does is pulls clean dry air into the crankcase from the inlet vent. That's why the oil filler caps that were used along with the road draft tubes were open and stuffed with steel wool. Allow fresh clean air in to replace the nasty vapour being pulled out. This is what keeps the acids and vapours from condensing inside the engine.

When the engine wears to the point that the blowby is putting more vapour into the crankcase than the draft tube or pcv can flow, it backs up through the intake part of the vent and oils up the air cleaners in the ones that draw their replacement air through the air cleaner.

Thanks Steve, I appreciate that answer!

 

[lewtot184]

there's no real downside to a pcv on the street. from what I've read here nobody has mentioned water. water is a by product of combustion and can accumulate in the crankcase (water vapor condensation). the pcv can pull the vapors out reducing oil contamination. the pcv can reduce carbon in the crankcase helping to maintain cleaner oil. all engines leak past the rings some; some worse than others. I just don't see a downside for a street car.

 

[furyus]

youn may not have a baffle in the valve cover under the pcv.

These are the types of answers I'm looking for. I don't have a problem using a PCV. I just want it set up properly. Some say the thread should have ended long ago, but with all the squabbling, and unhelpful answers, it can be hard to pull out all the good ideas. So now I know I need to check for a baffle on my aftermarket valve covers. I should block off the breather on the same valve cover as the PCV. I don't need a catch can. I don't want one. It will reduce moisture in the crank case. Maybe stop oil seepage from the engine. Thanks to all who posted useful info. I will give it a try.

 

[Ranger16]

I know how the PCV works, but not a single one have told me why I need to put crappy air in to my engine, and if that question is below your intelligence.....don´t read it!

Because it is far better to pull that air from the crankcase, replace it with fresh air, and burn it, than to leave it there to create sludge. It's as simple as that.