The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by Spanky65, Dec 11, 2015.
What's everyone's thought on running a PCV like this?
That's what we did on my brothers truck, seems to work fine.
Not sure the difference between PCV valves, but there are lots of them. Perhaps different weighted valves to open at different vacuum? Just my 2c, you might think about the vacuum of your engine vs a Tundra. Or a high lift/overlap cam vs. mild lift.
Do you know what PCV valve y'all used?
This is me thinking out loud, I would think a guy could temporarily add a T fitting between the intake and PCV and connect a vacuum/pressure gauge to it. This way you can see how well the PCV is working.
I think I might have use a push-in PVC valve in case I had to replace it. It would be easier that way, but very well executed.
It's not ideal, all you're ventilating is the valley under the intake manifold, but unless you want to add holes to the valve covers you don't have a lot of options.
You have created a "open-PCV" system. I personally prefer a "closed-PCV" system because the engine compartment will stay cleaner.
I set mine up like a mid 60's vette to the front fill tube. Too cheap to buy a vette one and just silver soldered a fitting in my old one, used in-line pcv to base of carb.
Small block Chevys of the early 60s had the PCV threaded in the back of the carb.
whats the difference?
A closed system has a pcv valve located in one part of the engine, usually either in one of the valve covers or in the valley of a v engine, and a fresh air intake that is connected to the air cleaner. During periods of low vacuum conditions, when the pressure in the crankcase exceeds the vacuum at the pcv, the fresh air intake allows the excess pressure to flow into the air cleaner where it is ingested into the intake system. So the system is "closed", it does not vent to the atmosphere.
In an open system the fresh air side draws not from the air cleaner, but from the engine bay area via a breather mounted on the oil fill tube, or a valve cover (the opposite bank from the one where the pcv is located), and when low vacuum conditions exist and pressure in the crankcase exceeds the vacuum at the pcv the excess pressure is relieved via the fresh air intake, into the atmosphere. The system is "open" to the atmosphere.
For SBC blocks with fitting on the back of the block and script or Turbo-Fire valve covers, 1963-ish to 1967:
Open PCV: Fitting on the back of the block with a rubber hose coming around to the front of the carburetor. The PCV valve is installed in-line. The venting comes from the vented oil cap in the oil-fill tube in the manifold. Since this vented to the open air, oil film was often found on the engine. This system was standard.
Closed PCV: Different oil-fill tube with a bung to screw in the PCV valve and a non-vented oil-fill cap. PCV valve screws into the tube and connects to the front of the carburetor (same place as the open PCV). The venting comes from back of the block using a metal tube and rubber hose, connecting up to the air cleaner. With this system nothing is vented to the open air. All oil fumes are captured by the carburetor and/or air cleaner. This keeps the engine much cleaner.
***EDIT*** --> Thanks Blues4U for the explanation!
I think you are OK, except I would match the PCV to the motor. What ever year your motor is look up that year camaro, vette etc. On my FE motor I put the PCV in the draft tube opening and the fill tube became the vent. Very similar to what you have and it works fine.
Here's a pic of the Vette set-up and the pcv that threads into the bung on the Vette fill tube.( 1964-65)
Hi Paul where do you draw the fresh air in from on your motor?? got a pic?
The only benefit I can see on a closed Positive Crankcase Ventilation system is filtered air entering the engine. JW
I had a 66 chevelle 327 that had the same PCV setup. factory holley carb on cast intake. The hole at the back of the block had a 1 inch pipe & hose connecting it to the air cleaner. You can barely see the pipe in the picture.
no pics Bob, but I'm running a vented breather cap on the fill tube. Seems to work okay.
You're not really ventilating the crankcase, all you're ventilating is the oil fill tube.
It keeps oil from the breather from getting on the engine or blowing up onto the windshield. The breather acts as both a fresh air inlet, when the pcv is directing crankcase gasses into the intake manifold; and as a vent to the atmosphere under certain conditions, like during acceleration or even at highway speed, when vacuum conditions are low and crankcase pressure exceeds the vacuum level. When it vents to the atmosphere oil droplets can exit along with the crankcase gases, and those droplets can form around the breather, the oil fill tube or the valve cover, or they can blow up onto the windshield. This doesn't only occur on engines with a lot of blow by, but of course, as the blow by gets worse, so does the oil from the breather.
I run a PCV valve, in a baffled gromet, behind the carburetor. Offy breathers, with foam and baffles, on the valve covers, serve as the inlets.
Yeah, the vette had a solid cap on the oil fill and vent tube in back. On later engines don't have that luxury, so I used the vented fill cap and figured this system would control internal eng. pressure and keep from pushing oil out of gaskets/seals, which it has'nt done for last 4 yrs. Correct, maybe not....do what I intended, I think so. Maybe I'll do it the right way this summer.....maybe not.....We'll see. I do think it's doing more than just venting to fill tube.
my 1970 chilton's manual says a pcv valve must be sized to the engine and should be installed vertically. any thoughts on that?
l00k at the carb picture Salt Flats has posted . The PCV is horizontal. and that's a factory setup. Almost every 2 bbl small journal from 1963 to 1967 had a vertical PCV valve mounted to the brass fitting behind the carb. and a vented cap on the oil fill tube. And they worked just fine.
The PCV on my 66 GMC 250 isn't vented. I have a oil fill cap that the PCV is installed in and its not vented to the atmosphere. Of course ive got a really good ring seal. I built the engine myself to very close tolerances. You can pull the PCV and rev it up and never see even a puff of blowby. I know it should have a vent. however I just didn't want to put any holes into the offy valve cover.
Thanks Blues4U. This is the best explanation of PCV. This is why I went with a closed PCV. I just rebuilt my engine and restored the engine compartment and I do not want any oil fumes messing up my work.
You are actually running a PCV and not a PVV. ^^^^^
When you run a PCV on one end of your lifter galley and the breather on the other end you are evacuating your lifter *galley (or valley as some call it). When you run your PCV in one rocker cover and your breather on the other you are forcing it you draw air through your crank case, this is what you want to happen. When you run it into your lifter galley and your breather on a rocker cover then again you are forcing it to draw through the motor and again you are evacuating your crank case. Air like water or electricity will follow the path of least resistance. When you put the breather on one end of the big hole and the vacuum on the other all you are evacuating is the big hole.
if I had a motor with a front filler neck I would either run a filler with the nipple already installed or I would braze one into the filler, cap it with a cap instead of a breather, and run an inline PCV like GM used in the '60s when they first started running them, then I would put my breathers in my rocker covers. If you have finned covers you can use a 90 degree moon type or if you don't want to cut your rocker covers because they are precious more precious than your motor you could actually put the breather on the side of the oil pan like they did with flatheads.
Ok the beaner has beat the sheep again. LOL
*I don't know that one is more correct than the other and if you must decide I am probably less correct than anyone else on this one.
Your correct many folks are over thinking it . The first small blocks with PCV drew vacuum from the back of the block and vented the fill tube. moving those two things 8 inches to the left and 8 inches to the right by placing them in the valve covers doesn't change anything. a engine with solid valve covers when warmed up the hot oil will wash out any condensation. The unburned combustion gasses excape from the cyl. bottom and will rise upward. My wife has a 2000 jeep grand Cherokee. 6 cyl closed system. And the intake and the PCV are in the one valve cover. you could install Both the PCV and breather vent in the same valve cover on a V8 and it would work fine.
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