I just wanted to start a new thread on PCV systems since Muttleys was more Chevrolet specific. Anyway, a couple of questions concerning PCV systems and setting one up on a motor that has been vented by a road draft tube: 1. Are PCV valves happier in a vertical orientation vs a horizontal one? It seems like all of the factory set-ups have the PCV valve in a vertical position with the top going to a vacuum source and the bottom pulling crank case fumes. In some of the custom systems, it looks like taping into something for pulling crank case gases is easier done with the PCV valve in a position other than vertical. Is position a factor in how a PCV valve will operate? 2. If a PCV valve is placed in the oil fill tube (with a sealing cap), could the road draft tube then serve as the vent supplying fresh air to the crank case? I know the road draft tube would see a little bit of a vacuum effect from air flow, but would it be more than a vent plumbed to the air filter/carburetor? This arrangement would not be as clean as a true closed system, but would it work?
I say NO, it doesn't matter how the PCV is oriented, save that it should be no more horizontal than just on horizontal. Reason being is that the valve has weight, and gravity would do it no assistance. That would work, IMHO, but a filter on the road draft would help keep the crankcase clean, which is the idea of a PCV in the first place. Better, of course, would be the PCV in the valve cover, and a filter on the RD tube, because that would be evacuating vapours from the whole engine. Cosmo
I would work from a junkyard tour rather than theory on vertical vs. horizontal--they are used both ways, and I would dodge thinking too hard by just choosing one used in that orientation in OEM. I think inlet/outlet choices regarding tube and vent could be swapped as long as the valve isn't placed in too much vapor or too close to liquid oil--but this consideration would tend to suggest keeping the draft tube location as the OUT side of the system. A badly placed PCV can suck oil. Closed system--I think this really matters mostly on tired engines, on which the crankcase is oft pressurized beyond PCV capacity by blowby, effectively forcing nasty vapors out the in door. The closed system simply routes tihe inlet side into the aircleaner so that if it becomes an exit, fumes still get burned. If your engine has an open system but has enough blowby to overcome it, you'll know by the smell.
So if you break it down to the simplest discription, air should ideally take this path. 1)In the breather on the manifold and into the valley. 2)Through the crankcase 3)On to the PCV (which should be oriented with the flow toward the manifold) 4)Into the manifold where it is dealt with and spit out the exhaust. I'm hoping I didn't get the location and orientation of my PCV jacked up. I just picked one off of the rack that was small and had fitting I thought would work. It's horizontal.
I respectfully disagree based on my very unscientific experiments. I had a cabinet full of PCV valves. If you suck on most in the vertical position, they work as designed. The vacuum lifts the heavy plunger. When the vacuum stops the plunger falls back to it's seat. No air passes the seat if you blow into the valve. (backfire) When I hold it horizontally the plunger opens fine but when the vacuum stops the plunger just laid on it's side off of it's seat. You could easily blow through the valve. It took a lot of pressure to force the plunger over to it's seat when on it's side. The ones I played with rattled when shaken leading me to believe that there are no guides to keep the plunger centered in the valve. Guides aren't needed when they are upright. I did find a PCV valve that came from the factory in a horizontal position. A 1994ish Isuzu Trooer II V6. It's plastic so you can see that it is spring loaded. It doesn't rattle. When the vacuum stops the spring pushes the valve back to it's seat. The good ole suck test confirmed that it worked horizontally...open with vacuum closed with no vacuum. my flathead application. The valve after the hose bib was cut off on the right side. The valve is made for hose connections on both sides. I cut one off for this set up. I painted the plastic valve to look better. P.S. The breather is a fake. I welded up the hole so it's just used as an oil filler cap. I have pan breathers for the air to enter engine. Try the good ole suck test if you have a new one and see if you don't agree.
Tommy is right , most won't work good on there side!! But some are made to work on there side, mostly foreign screw ins JimV
I don't see a real answer here ? Am trying to add an PCV to my 55 Y-block Ford. Found that my engine had most of the components from what is the later Truck engines, but was not tied into intake manifold they had rather unceremoniously draped an half inch hose over the side of the block and guess they thought it would Draft ??? Found what is supposed to be correct PCV valve with 1/4 inch threaded end and looking for 45 degree street elbow that it is supposed to have to use it in intake manifold ? The heavy plunger inside valve will fall by gravity but im not sure spring would push it back up mounted at 45 degree angle? Chris, shows you to have an 55 Mercury do you still have y block? what did you do with yours? Thanks
I did a little investigating about using a PCV in the horizontal position and bought a NAPA 2-9255 which is supposed to work that way. I don't think it would work in a vertical orientation. IIRC it is one that was used on the Chevy small blocks. The valve has a 1/4" MNPT on one end and a 3/8" hose barb on the other.
NUMBER TWO -- NO! Do not flow the vent system backwards. Always consider the old road tube the EXIT. If you want a pcv on on the road tube or at that end, after the airborne oil particles go thru the baffles or calm chambers and drop out of the air first, ok, but don't pull out the dirty vapors thru the front INLET where there are no baffles, and the timing chain is stirring up and slinging out a froth. That would be the worst place to pull air from. If the factory designed a certain direction, it's best to work along with their design and not fight it. DONT VENT BACKWARDS. WHY BE ORDINARY ?
After I put dual quads on my Y-block, I pretty much gave up on the PCV system. There was going to be too many obvious hoses to make a true closed system work. My intention was to pull crankcase gases out of the fill tube through the pcv, mounted vertically on the back of the intake. That would take care of high manifold vacuum situations. For low manifold vacuum (high venturi flow through carb), I was going to pull gases from the exsisting road draft tube, mounted on the side of the block, through a baffled breather connected to the air cleaner. So, from that description, you can see how things would end up looking like a 70's smog motor!
My engine has no road draft set up, no hole in block, it is later truck motor as best I can figure out?(60 to 64) Information I have been able to gather up shows trucks with a PCV that uses hole in front of carburetor on manifold with 45 degree street elbow and tube from adapter on valley cover that runs along side passenger valve cover to the PCV in the Street Elbow. Fellow on Ford barn sent me illustration he found but I dont know how to forward it. It calls for an V1 Standard PCV Valve I found Standard V100, and 45 degree street elbow too. Not a lot of room where it goes and may have to remove carburetor to get old fitting out of manifold.
On my Ford flattie I have a standard (free floating ball) valve dead horizontal in the former road draft tube location, with incoming air from the filler cap. I thought it was working fine but after reading this maybe I should switch valves, although I'm not sure what role gravity actually plays, maybe the way I have it it takes less vacuum to pull it off the normal bottom end, but what are the ramifications of that?
Blue One That is exactly how mine is going to be set up! Think I have all of it now, just have to remove the fitting that is in the manifold now without breaking it off I think it has grown to the intake! Have also heard this is referred to as an Anti back fire valve?????
Today if I were installing one I would figure out how to use an oil separator in the line. I have them on the 2 car I own not hamb friendly and both show oil in the holding area of the system. One of them is on a 2018. My 56 still has the draft tube.
Jimmy Six, I did see something today about those and I agree it is probably a good idea! My old 55 back in 57 to 64 had the road draft too and used to remove and clean it. But there is no place for one on this block. an 302 GMC would be a good choice in it too!
To the second part of your question Think where the road draft ends could you pick a dirtier location to pick up air. Down low and behind the front wheels is not a good place to be pulling air into your engine.
Road draft tubes do not pull air into your engine. They are placed where airflow will create a slight suction on the tube and relieve internal crankcase pressure from the engine. Air is coming into the engine usually from a breather on the oil fill tube or other breathers on the valve covers etc.
If you look at his question he was talking about using a PCV valve and using the road draft tube as a vent. In that case it would be pulling air in the tube.
So, I’m correct in that the intake of air into the engine is properly done using the breathers on top of the engine. Yes drawing air down low is a bad idea.
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