PCV or not?

[janbanan]

To be honest I´m getting a bit confused. How can pressure build up in crankcase when pcv is gone and with a totally open breathing thru catch can to the road? My car have a hose on just one of the valvecovers, the other one is closed, is that bad?
I can understand that vacuum only exist in low speed,but when I think of it, that means pcv is closed in full throttle and I have no other breathing on my engine?

 

[RJRENTON]

Gentlemen,
Others have accurately stated the function of the PCV system and its reasons for the engine. It appears that a "catch can" is basically a liquid-vapor seperator.
An important consideration of the PCV system is the recovery of unburned hydrocarbons coming from piston blow-by and reintroducing them back into the engine to be burned. In addition, the PCV system helps to eliminate accumulated moisture in the engine. Most or the newer aftermarket carbs have provisions for the PCV system. Some guys choose to cap off this port with out re-calibrating the carb's primary circuits. This will result in a rich primary condition that may or may not be adjustable. It is my opinion that the benefits far outweigh the disadvantages.....but "you pay your money and take your choice"....
Bob Renton

 

[RJRENTON]

I think booze explains a lot here. I'm giving him a pass.

Fortunately for most of us, he was just operating a computer and not a motor vehicle. For personal reasons, I have ZERO tolerance for drunk drivers.....
Bob Renton

 

[747mopar]

To be honest I´m getting a bit confused. How can pressure build up in crankcase when pcv is gone and with a totally open breathing thru catch can to the road? My car have a hose on just one of the valvecovers, the other one is closed, is that bad?
I can understand that vacuum only exist in low speed,but when I think of it, that means pcv is closed in full throttle and I have no other breathing on my engine?

Breather on one side pcv on the other. As far as not having vacuum under full throttle goes, if it's a street car than 99 percent of the time it's making vacuum.

 

[dvw]

Apparently there is some confusion as to the function of the PCV system. It is a loop. Air enters the breather, vapors are pulled through the crankcase through a small controled orifice to be burned in the combustion chamber. If there is poor baffling the system will draw oil causing issues. The PCV can not create crankcase pressure as there is an escape route through the inlet side at the breather. Now if the inlet (breather side) is restricted, PCV mounting area poorly baffled, or the engine has excessive blowby the system can be troublesome. Proper baffling and enough breather area are should take care of any issue aside of a worn out engine.
Doug

 

[Lelo 500]

It's like talking to a wall.
I have never had so many disagrees before.... BTW, ever seen the underside of the valve covers of a engine without a PCV or evac system?

66chargerpat- The PCV helps keep moisture and nasty stuff from building up inside your crankcase and shortening the life of your engine.

MOPOWER871- Please share why you disagree.

 

[Zeppelin264]

Here's a simple picture of how it works.

 

[Ranger16]

I can understand that vacuum only exist in low speed,but when I think of it, that means pcv is closed in full throttle and I have no other breathing on my engine?

The PCV operation is regulated by vacuum, not speed. Anytime the throttle is closed or steady (at cruise at any speed) you will have high vacuum and PCV operation. Conversely, open throttle (not necessarily "full" throttle), equates to vacuum lowering in proportion to the throttle opening. Thus you can have full PCV operation cruising at 70 MPH. Throttle up to pass someone and the vacuum drops and the PCV closes.

Personally, I would not operate my engine without POSITIVE crankcase ventilation.

 

[Ranger16]

A catch can is simply a vessel that allows the suspended particulate (oil, water) to cool, condensate, and deposit in the vessel while the air continues on its way back through the carb. It is generally used in conjunction with the pcv valve.

That statement right there answers the OP's question. Think about it for a second, without the PCV, the crankcase air can't be pulled through the catch can in the first place. It is virtually useless without the PCV.

 

[furyus]

View attachment 557446

Here's a simple picture of how it works.

Ok. So, it shows a hose going from the breather on the passenger valve cover to the air cleaner. Is this also needed for proper function? My car currently has two breathers. Neither connect to the air cleaner. One on each valve cover. Drivers side also has the PCV towards the rear of the valve cover. Will two breathers have a negative effect?

 

[janbanan]

Wow.....! This was fun but I still don´t get it. I thought engines worked the same way as us humans,breath in and blow out?
As I said I have only one opening to one of the valve covers. I need to drill a hole in the other one if I want it to work as the sketch above.
In the seventies I used to race rallycars and volvo engines had a steelpipe straight out to the road. Racemanagement didn´t like that (because of the oil spill) so we took a plastic bottle with drilled holes, working as a catch can I guess. We didn´t want bad air into the engine.
I have not checked on this car, but if you put your hand on the end of ventilation you can feel it is a firm blowout, so bad air sure blows out.
This is not my daily drive I use it to impress the ladies with donuts and driving sideways.

 

[747mopar]

In the sketch above you can eliminate the hose to the filter by just putting a breather cap on that side but yes that's how it works, air in, air out.

 

[Lelo 500]

Ok. So, it shows a hose going from the breather on the passenger valve cover to the air cleaner. Is this also needed for proper function? My car currently has two breathers. Neither connect to the air cleaner. One on each valve cover. Drivers side also has the PCV towards the rear of the valve cover. Will two breathers have a negative effect?

It would be much better if the PCV is on one valve cover and the breather on the other valve cover. Then the clean air is drawn in on the breather side goes across and through the engine and out the PCV. With the breather beside the PCV it's not doing much and probably only drawing from the breather beside it. The path of least resistance.

 

[Zeppelin264]

Ok. So, it shows a hose going from the breather on the passenger valve cover to the air cleaner. Is this also needed for proper function? My car currently has two breathers. Neither connect to the air cleaner. One on each valve cover. Drivers side also has the PCV towards the rear of the valve cover. Will two breathers have a negative effect?

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.

 

[383man]

Ok. So, it shows a hose going from the breather on the passenger valve cover to the air cleaner. Is this also needed for proper function? My car currently has two breathers. Neither connect to the air cleaner. One on each valve cover. Drivers side also has the PCV towards the rear of the valve cover. Will two breathers have a negative effect?

When they put the valve cover breather hose to the air cleaner they called that a closed PCV system. It just took the air the PCV system pulls in through the crankcase to be cleaner air because it was now pulling air after it went through the air filter. And actually some were made so when the car was floored and the vacuum dropped to zero and the PCV valve shut any crankcase pressure building at WOT can actually be pulled back into the eng through the hose going to the air cleaner to still relieve any crankcase pressure at WOT. The other type with the breather on the valve cover and no hose just vents the crankcase to outside air at wide open throttle. Ron

 

[khryslerkid]

When they put the valve cover breather hose to the air cleaner they called that a closed PCV system. It just took the air the PCV system pulls in through the crankcase to be cleaner air because it was now pulling air after it went through the air filter. And actually some were made so when the car was floored and the vacuum dropped to zero and the PCV valve shut any crankcase pressure building at WOT can actually be pulled back into the eng through the hose going to the air cleaner to still relieve any crankcase pressure at WOT. The other type with the breather on the valve cover and no hose just vents the crankcase to outside air at wide open throttle. Ron

Ron to the rescue!

Three pages of posts just to explain how a PCV works.

 

[miller]

Hehe...real popcorn stuff!

 

[Ranger16]

Ok. So, it shows a hose going from the breather on the passenger valve cover to the air cleaner. Is this also needed for proper function? My car currently has two breathers. Neither connect to the air cleaner. One on each valve cover. Drivers side also has the PCV towards the rear of the valve cover. Will two breathers have a negative effect?

What you have is crankcase ventilation, not POSITIVE crankcase ventilation. Not necessarily a "negative" effect. More like very little effect.

 

[janbanan]

Hehe...real popcorn stuff!

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!

 

[miller]

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!

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.

Un-burned gases, besides blowby, and oil itself (once the engine starting to wear), turned into a no-no, according to the EPA.

That PVC valve simply re-directs un-burned fuel vapor (in a engine in good shape), back into the intake manifold, via the carb base. More so-called air quality. Most piston engines are NOT designed to completely burn all the fuel mixture. So, you get those fuel vapors.

If you don't like the results...mount up a dump tube!

Understand that does not give you the answer you want. Just a fact, engines must have a way to breath, to work right. If you don't want a PVC valve hooked up...don't.