Closed Cap or Breather?

What is the difference in using a closed oil cap or a breather cap?

I am running a pcv valve off of the other valve cover?
[addsig]

I would think that there has to be some clean air coming in somewhere to replace the blowby and fumes that the PCV is pulling out, or else the PCV would tend to pull air through the seals. I would use a filter, just in case the PCV ever stops up. I don't know if it's a good idea to run a positive seal on your PCV system. Anyone else have ideas??
[addsig]

HI
I agree with bluestreek. The PVC needs to draw fresh air from some where. So there needs to be eather a breather cap on the other valve cover or in the valley pan. The choice of most is the valve cover.
Tim
[addsig]

You need a breather cap on the other side.

It can be just a breather with it's own wire mesh filter or a breather cap attached to the air cleaner via rubber hose which would reclycle clean air into the valve cover.

dave

why do you need air comeing in, the rings seal better with a crankcase vacum, that is why some cars run a vacum pump for crank evac

any other opinions

Engines from day one have had to have some type of air breather for the crankcase/valve covers. Before Emissions they just had a open tube. In Nascar racing they used a tube into the header pipe to vent or draw a vaccuum at high RPMs. On the street it came down to a PCV and breather to allow air in. Now we use vaccuum pumps. If you draw a vaccuum only with no way for air to get in, it has to come from somewhere. Either gaskets will leak in then out when pressure is higher or it'll pull it in threw crankseals.
One thing a lot of people have never given much thought to because on gas engines you don't see it that often and then it usually gets blamed on something else is a crankcase explosion. If you don't keep the fume explosion level below a certain point you'll have a explosion. You need to allow air in & out of the crankcase.

under a vacum there is not enough oxygen to burn, those vacum pumps can create 15in/Hg or more of vacum

gasoline can not ignite without oxygen

what the pump is pumping out is the blowby of the rings, all motors have blowby some more than others. there is nothing in the crankcase to ignite.

OK ... I get kicked in the head every time I get involved in this discussion, but here is my two cents ... and trust me on this one ... "It ain't Rocket Science".

Lordviper hits the nail on the head ... No one has rings that seal 100%.

Because of that, every engine will generate internal pressure no matter what.

Eventually that pressure must escape and it will ... whether its through your seals (creating oil leaks as it goes) ... or through open breathers of some sort or through some assited evacuation method, namely a "Draft Tube" ... "Positive Crankcase Ventilation" ... or some "Mechanical Vacuum" system.

Point #1 would be ... I'm not so all fired sure how important it is to have a so called "Fresh Air Inlet" as a part of this system ... Not that I think it's a bad idea, but logic (and simple looking at running engines) tells me the pressure inside the engine is going to be escapeing through that "Inlet" more often than any fresh air will be comming in through it.

My sense of it is that as long as that pressure can make a "Free Flowing" escape without creating pressure on the seals within the engine ... you've got it 95% whipped ...

Obviously, the EPA has some ideas of what it thinks is safest for the environment and I will agree that if you can create some sort of directionl flow via vacuum, from a draft tube or some other means, that it will assist the process.

I know guys will say that Gasoline vapors will accumulate in the crank case and dilute your oil if you don't run some sort of vacuum evacuation ... but dang, if you have that much blow-by you have problems bigger than crank case evacuation and you are probably having to refill the oil (if your rings are that bad you must be burning a ton of it) often enough that you are "un-diluting" it as fast as your blow-by is diluting it.

In the final analisis ... My thinking is that as long as the pressure can "exit freely" and I do regular maintenance on my engine I'm happy.

I do not run "PCV Valves" in any of my engines because I think is is just one more place to have a "tuning" problem. I also don't vent directly into the environment either.

OK ... I've grabbed my ankles ... You'all can start Kicking

BTW if you want to kick me in the head, it's out front ... the boney thing in the back is my A$$ [img]/phpBB/images/smiles/icon_biggrin.gif[/img]
_________________

Larry Madsen
Las Vegas Nevada



<font size=-1>[ This Message was edited by: monstermach on 11/15/02 7:39am ]</font>

<font size=-1>[ This Message was edited by: monstermach on 11/15/02 9:09am ]</font>

<font size=-1>[ This Message was edited by: monstermach on 11/15/02 9:14am ]</font>

At least yours is bony!

OK MONSTERMACH
How do you or how do you not vent it then??
I pluged one off one time and the motor just didn't sound right..
Tim
[addsig]