PCV question

296 V8 · Sep 11, 2012

As always this subject brings out a ton of misinformation - myths - wives tales - voodoo.

A PCV valve isnt magical its nothing more than a simple check valve …. The reason for it is to stop the entire motor from exploding when it backfires / fire inters the intake system.
(Iv seen what happens when blow by is set off ….. It easily launches valve covers.)

There is more oil mist guaranteed under a rocker cover than in a lifter valley (in a sbc)

Your setup should be working without sucking oil.
Are you sure you have the correct oil level in the pan? / crank isnt swimming?

　
I’m running this setup w no oil use. Simply pulling a vacuum across the valley w no baffle at all.
Additionally this is off road / this motor has been on its side - nose - and standing strait up.

common everyday tube and cap

welded fitting into soft plug - 3/8 hose - valve >>>> up to carb

Nick O · Sep 9, 2012

I understand the simplicity of your system, and the overall simplicity of the PCV system as a whole. I actually had mine hooked up like yours at one time, before I switched this way. Simply air in, air out. Really should not matter if the valve is in the tube or the carb. Oil level is five quarts. Vacuum at the valve is 15 at idle, 21 at cruise, jumps up to 25 at deceleration for a quick second or so. I also closed everything up, disconnected the PCV and checked and have a little pressure on the sytem which should eliminate an intake gasket issues, I have no vacuum in the crankcase with the PCV unhooked and everything plugged. It is very obvious the oil is in the clear hose from the tube to the center carb.

cvstl · Sep 9, 2012

In the above diagram, the intake air uses the draft tube hole.... not trying to beat a dead horse here, just wondering if that makes a difference. If the draft tube passage gives a less direct route for the air, it would reduce the air velocity at equal vacuums not allowing the oil to stay suspended and suck up into the tube. Its the only real difference that I can see in what you described and the diagram.

296 V8's also looks to be drawing through a draft tube hole....... still just wondering.

Nick O · Sep 9, 2012

Did the early engines that had the front intake mounted fill tube/vent also have a matching passage in the block, that connected it to the front cover area of the block, not the valley? So if it's a "late model" block the fill tube won't be working as designed, therefore I will have to baffle the fill tube. Can anyone please confirm this for me, I think I actually remember that old china wall in the front being different on early SBC engines using the old style fill tube.

cvstl · Sep 9, 2012

I can look in the morning, got on sitting in the back of my office.

chubbie · Sep 9, 2012

the Fram PCV number FV100 is threaded on one end and a slip to hose on the other. what number PCV would be a slip on both ends and have the "spring" in it?

hanginlow58 · Sep 9, 2012

hey nick O , here is how i got that system to work that i told you about, the vette fill tube did come baffled but was not enough i also had oil still sucking into my clear test tube so i got some copper pot scrubber material and made a wire going through it so i could pull it out for adding oil and to keep it from going further down the tube, pcv mounted at carb, temp. breather at rear of manifold, i tested this good today went on a little reliability run today up in the mountains and flying down the freeway with no sign of oil in the clear tube or blowing out anywhere.

now i just have to hide the plumbing better, the trick to this is the oil baffle system, i believe it would have worked the way i had it before if i would have made a factory type oil baffle under the intake.

26 T Ford RPU · Sep 10, 2012

The photo in post # 29 gives a good view of a pre 68 small block, the round thing is factory baffle i mentioned and the hole in the centre right in the front of the block is where the filler breather pipe sits above. JW

cvstl · Sep 10, 2012

Here is the valley of a 283. Fill tube runs down into the block, draft tube hole appears to vent both the valley and case. Looks too me like this significantly changes the air flow patterns.

norms30a · Sep 10, 2012

When you look down the oil fill hole can you see the timing chain? If so then most of the air will still pass through the valley, wouldn't it? Because of timing chain holes on either side of the fill tube?

I am doing this to my car now so I am studying this thread in hopes I don't screw up.

no55mad · Sep 11, 2012

Be sure to get the correct valve. A PCV that screws into the oil fill tube (like the Corvetts used) flows the opposite of a valve that screws into the base of the carb.

Nick O said: ↑

Ya believe me I appreciate your help, everyone's help for that matter. It was my understanding the the valves were basically the same with the only difference being the flow. The one from the tube would obviously flow from the threads to the carb. You may be right, could I have too much pressure at the valve? It is sucking that oil vapor and mist up a 6-1/2 inch tube to the center carb. Someone posted earlier in this same thread that orientation of the valve should not make any difference. I am really baffled, no pun intended.
Click to expand...

Nick O · Sep 14, 2012

Not to keep this thread going forever but often I have seen where a thread died an the issue resolved and no one knew the answer. I have not fixed my problem yet but I will inform everyone of what i have done in the hopes of maybe someone can help me and I can in-turn help someone else with a similar problem. I took the original stock oil fill tube and welded a a solid washer on the bottom of it. after welding on the washer i drilled about (10 ) 3/32 holes in the bottom of it, I then stuffed it with copper pot scrubbing material all the way to the top. I then sealed the top and attached a 1/2 nipple which i hooked to the rear of the center carb which has a fram fv100 screwd in PCV valve with a piece of clear 1/2 inch tubing so I could see what was in the tube. Filtered air is coming from the back of the manifold which is drilled and tapped through the coil boss up and into the rear air cleaner with a 1/2 inch hose. No breathers on the valve covers. The system is much improved but not totally fixed by any means. Still sucks oil through the temporary clear hose from the fill tube to the PCV, enough that you can see actual droplets in the hose around the connection to the PCV and a minute mist in the hose. The spark plugs have cleaned up considerably but still trace a very small amount burnt oil on them towards the intake valve position.

34toddster · Oct 15, 2012

Nick O, I'm watching this with great intrest, a friend of mine is installing a motor with no valvecover holes and a late model block I think he's in the same boat. Thanks

CB_Chief · Oct 15, 2012

Jimv said: ↑

If you're running a PCV & a"Breather" it is NOT a PCV system!On a PCV system the other breathing port is a tube into the air filter from usually one of the valve covers. When the car is accelerating it is NOT drawing thru the PCV valve, that is were a tube to the air filter would come in & draw fumes out of the crankcase there by positively ventilating the crankcase & that give us the "P" in PCV!lol
JimV
Click to expand...

Jim,

I have a 1963 283 that I know the history for since, well 1963 and it came with a PCV valve set up and has the oil fill tube with a vented cap on the intake. It has the soup can in the lifter valley and a weird plug (resembles a small A-arm bushing) where the draft tube normally goes that has a steel tube that curves around the distributor and connects to the PCV valve screwed into the Rochester 2G carb base with a short piece of rubber hose. Reckon GM knows that it won't work?

Jimv · Oct 15, 2012

CB_Chief said: ↑

Jim,

I have a 1963 283 that I know the history for since, well 1963 and it came with a PCV valve set up and has the oil fill tube with a vented cap on the intake. It has the soup can in the lifter valley and a weird plug (resembles a small A-arm bushing) where the draft tube normally goes that has a steel tube that curves around the distributor and connects to the PCV valve screwed into the Rochester 2G carb base with a short piece of rubber hose. Reckon GM knows that it won't work?
Click to expand...

Thats a "open system".Closed system was better!(?)
JimV

tommy · Oct 16, 2012

A little definition is in order...An open system was the first iteration of a PCV valve. The breather was OPEN to the atmosphere. They learned that under heavy loads the PCV valve could not handle the volume and the gasses escaped into the atmosphere. Bad if you are an environmentalist. So they mandated a closed system.

A closed system has the breather inside the air cleaner. The white filter material replaces the push in oil breather. When you buy one from a parts store it is called a breather element. Now when the system backs up due to heavy loads, the gasses back up inside the air cleaner and are sucked down the carb. This only occurs under heavy loads if the engine is in reasonable shape. Normal loads the air enters the PCV system through this filter element. Most hotrodders are not too overly concerned about the pollution that our relatively few hotrods put out. I have replaced some doing a tune up where this was soaked with oil on a worn out engine.

I personally don't have a closed system on any of my hotrods. The polar ice caps are not in danger from my few hotrods.

A PCV valve is more than just a check valve although it does work as one if the engine backfires preventing a pan explosion. A PCV valve modulates the air flow through the engine so that it flows less air at idle which would be a big vacuum leak messing up the idle. Under a heavy load like accelerating the vacuum drops but the valve is made to pass more gasses internally when it is needed more. Just the opposite of rational thinking which confuses a lot of people. It is how it's made internally.

gatz · Oct 18, 2012

Different brand, but assuming the principles are the same; what would work on a '56 331 hemi?

Which of these ideas look feasible ?

1) Put a baffle in the valley so that the air-flow goes from the Fill Tube down into the crankcase and back up through the valley to a fitting in the rear of the HotHeads valley cover; then to the PCV on the Carb via a hose.
A tube or hose would run from the air cleaner ("clean air") to an adapter on the Fill Tube Cap....much like what tommy has posted.
This won't scavenge the valve covers at all.

2) Braze some fittings onto the rear of the valve covers, screw in some 90º fittings and run some steel lines from each side to a "T" and then a line under the intake manifold to the PCV on the Carb. see pic.
Use the same arrangement as #1 for the Fill Tube.

In any case, it seems that there's not a lot of volume needed at the PCV; aren't they about 3/8" ID hose?....... so maybe for the 2nd idea, a smaller tube (say 1/4") could be used from the valve covers to the "T" and then a 3/8 tube or line.
Also, would having a low-point anywhere in the line cause a problem?

26 T Ford RPU · Oct 20, 2012

The fitting at the carb end maybe about 3/8'' but if you have the same size or smaller at the motor it cause the air/gasses to flow fast inturn pulling more oil with it and also causing a flow restriction.The car manufactorers got the sizing right and its not new. JW

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