An open system simply means that your airfilter is "open" to the air on all sides. Be careful which air filter set up you get because as i found out the hard way, some are not getting as much air as you might think. On my old 66 289 A code. I went with an edlebrock air cleaner. Imagine my surprise when the guy told me the optional high performance cleaner ( the one with the blue base and orange filter with circle screen) would be a better breather even though it was about half the diameter. The reason? The edlebrock is a dished out bottom that actually blocks over half the filter from air. It has to do this so it will fit underneath the hood without banging into something. You will need a breather element for both the breather side and the pcv side so it will filter the oily air that comes out of both of those. You could leave it open to air but you risk getting oil all over your engine from the fumes and its not very nice for mother nature. Whatever you do , don't block off either one or else you will start pumping oil past your rings like mad... Hope this helps ya!

 

A closed system recycles cylinder blow-by back into the intake to make a second attempt at burning the raw fuel. An open system just lets the blow-by gasses into the atmosphere instead of back into the intake.

I think you get 2 small plusses with the open system. A better looking engine and a tiny increase of performance. The blow-by gasses are hot and have some burnt fuel that doesn't burn well the second time around.

IMHO

 

I'd wager to say that there is a lot more oil than unburned fuel in the blowby mixture by the time it gets up to the valve covers, but then again i may be wrong. A closed system is easier to keep clean (on the outside), but gunks up your intake system. Not so bad on NA, but on forced induction engines this tends to dirty up your intercooler.

 

Hmmm... interesting responses. Is your '65 basically stock? Most 65s didn't have a PCV but, rather, a system called a "Road Draft Tube" -- a pipe (about 1" diameter) that came off the back of the intake manifold and went down the back of the engine and hung down under the car on the passenger side. The way it worked was that airflow at driving speed would create a "draft" across the end of the tube and evacuate the crankcase of blow-by gasses, etc. Worked well - so long as the car was moving. At any rate, you speak of a hose from your valve cover so it sounds like your setup is not stock. A "closed system" doesn't permit blow-by gasses to simply bleed into the atmosphere like the Road Draft system or as on engines that simply have a breather cap (or two) on the valve covers. Rather, typically, you should have a breater cap on one valve cover and a PCV ("Positive Crancase Ventilation") valve on the other cover. A hose then runs from this valve to your intake manifold allowing blow-by gasses to re-enter the combustion cycle and become more completely bured off. The breather on the opposite cover allows fresh air to be drawn into the crankcase while the PCV evacuates. This is a "closed system."

Short answer: Your description sounds like your breather cap is designed to take it's fresh air after having been filtered by the carburetor air filter. A pretty good setup but if you don't want to use that hose change the breather for one that has an internal filter. The PCV doesn't need to be changed. You will still have a "closed" system.

- Gord

 

Typical open system consists of 2 open air filter breathers one on each (available) valve cover. Sometimes you may find one breather with a long draft tube running under the car. The breathers have various types of elements, some are fiberglass packed, some are paper filters and some are wet gauze types, ((avoid the ones with no internal filter or packing)). In this type of system any type of blow by or unburned fuel passed into the valve cover on the compression stroke are vented directly to the athmosphere (and creates a dirtier engine compartment if you have a tired engine).

A closed system consists of an Open air breather which is typically an element on one valve cover or a breather cap and then on the other valve cover is a PCV valve. The valve has a little ball or plate in it that when the engine pulls a lot of vaccum the valve shuts off (preventing the engine from sucking oil up into the manifold...suck on a "new clean pvc" and you'll see what I mean) and at that point the breather element stablizes internal engine pressures. In a healthy engine typically there is not a whole lot of blow by at idle, if there is you have bad rings or valve seals. As the engine moves up the rpm range and looses vaccum the shut off device in the pvc opens again and the gasses inside the engine, cause by blow by and normal wear on the oil, is permitted to travel into the clean side of the air cleaner and be re-absorbed into the combustion process. You do not want to connect the pvc to direct manifold vaccum as this will suck oil right into your combustion chambers (albeit a small amount, but it still isnt good), the air filter chamber (clean side) permits a good place for the vaccum to be equalized prior due to the air filter actually passing air where if attached to the manifold the only place to pass air is through the pvc as the throttle plates limit vaccum. Basically, make sure your pvc is attached to the air cleaner housing (some cars attach the blow by hose to the diry side on enclosed element air cleaners and others to the clean side if running either a closed or open element air cleaners. I have seen it a couple different ways.

So maintenance. You would want to replace your blow off hose every year or 12000mi along with your pvc valve (or as recommended by the parts manufacturer). These devices corrode and the pvc inner working become stuck and either over functional open(excessive oil consumption and oil burning) or non functional continuously closed (the pressure inside the engine is vented through gaskets and leaks occur). Also, use a quality oil breather cap with good packing as it filters any air coming into the valve covers and into your engine. Most cars have breatheable caps on the valve cover and others filters located in various places including the dirty side of a closed element air cleaner housing. You want to replace your valve cover breathers or line filters when they become heavy feeling or once every year or 12000 miles or as recommended by the valve cover breather manufacturer.

Finally, if you notice that your air cleaner on the clean side is getting all oily and your carb is getting dirty. There is some sort of engine problem. Worn rings, bad valve guides, bad pvc, bad tuning, blocked valve cover breather etc. You can clean the carb and other parts with a carburetor cleaner and they have routine maintence methods printed on the packaging.

Hope it helps.

 

Hmmm... interesting responses. Is your '65 basically stock? Most 65s didn't have a PCV but, rather, a system called a "Road Draft Tube"

Unless it's a California car - I believe Cal mandated PCV systems a little earlier - maybe 1963? than the rest of the US in... '66?

 

My car was basically stock, but I believe it was a california car ( I have the original California black plates ). I currently have the car setup with the pcv valve still intact and a open element filter on the opposite valve cover. This sounds like it might work ok.