PCV

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Ayr Hed
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PCV

Post by Ayr Hed »

switching from Corvair Talk thread.......re: air cleaners...ordered custom aircleaners for my 110 twin carb motor...no provision for PCV....at Corvair 1 site, I read the "tutorial" on running a road tube to deal with the no provision for PCV on these aircleaners...my PCV plumbing has a "bypass ?" that runs between #3 and #5 through the shroud..if I plug off the hose that goes to the aircleaner, will that be sufficient to avoid fumes entering heater/ passenger compartment ? Tutorial mentions using a '60-'61 roadtube that runs through shroud then between cylinders...I assume that the current bypass dumps out into fan air flow ?? If so will this provide adaquate PCV ventilation ??..if not, and I need to run the road tube..will it just slip in through the top of the shroud in the current hole ?
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'64 Monza coupe 110/4 spd

64powerglide
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Re: PCV

Post by 64powerglide »

I don't know why GM figured they needed that bypass hose going to the air cleaner, I would think the vacuum tube would work fine for venting the crankcase. Just cap that fitting & see how she works.
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bbodie52
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Re: PCV

Post by bbodie52 »

I believe it has to do with the engine speed (RPM) and the state of intake manifold vacuum at different throttle positions. In some operating conditions, intake manifold vacuum is high and draws crankcase fumes effectively through the PCV valve or fixed orifice (a calibrated vacuum leak). But if the throttle is opened wide, intake manifold vacuum may drop, while crankcase pressures increase as the engine works harder and spins faster. If the vacuum port fails to draw off enough crankcase pressure, it has to have someplace to go (other than out through the dipstick tube, while spraying oil all over the engine). That is one purpose of the link to the air cleaner — to permit the crankcase to "breath" as filtered air and excess fumes are allowed to be drawn in through the carburetor throat.

It is critical that the parts of the PCV system be kept clean and open, otherwise airflow will be insufficient. If you close off the air cleaner portion of the PCV system, you will likely be giving your engine an oil bath from time to time as excess crankcase pressure exits via the dipstick tube — forcing crankcase oil up the tube along with the pressure and spraying oil everywhere! :nono: :sad5:

If you want to know more, you can use the following link to read a Wikipedia article. I have also included a series of videos to further explain the PCV system. The key is to keep it operating as the engineers designed it. All parts of the PCV system are essential to allow it to operate properly, reduce crankcase pressures and to reduce oil contamination.

:link: http://en.wikipedia.org/wiki/Crankcase_ ... ion_system



PART 1


PART 2


PART 3


PART 4


PART 5


PART 6
Brad Bodie
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Image 1966 Corvair Corsa Convertible

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Ayr Hed
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Re: PCV

Post by Ayr Hed »

I hear you Brad....what have other guys done to address this issue of no PCV provisions on custom air cleaners ? Run a road tube without the PCV valve ? That's the way it was done on Granddad's 1951 Pontiac !
'64 Monza coupe 110/4 spd

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Re: PCV

Post by bbodie52 »

The videos above point out that the early engines that were equipped only with a road draft tube ended up with sludge buildup and oil contamination as the blowby caused excessive crankcase contamination that was not handled adequately by the road draft tube system. The engines did not last as long and the air was contaminated by the crankcase exhaust fumes from millions of road draft tubes. The development of the PCV system greatly improved crankcase ventilation and reduced the development of oil contamination and crankcase sludge. At the same time it reduced smog and air contamination by burning the crankcase fumes before they exited the engine via the tailpipe.

In your other post I included some photos and a link showing how Corvair owners have modified the Corvair PCV system to function as originally designed with custom air cleaner systems. Here is that link...

:link: http://www.persh.org/Corvairs/PCVsystem.htm
Brad Bodie
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64powerglide
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Re: PCV

Post by 64powerglide »

I would think with the throttle wide open your vacuum would be at maximum in the balance tube but as you said more pressure build up might be more than it can handle even at maximum vacuum. Is it possible to put a vacuum gauge on each inlet & see how much vacuum it has at different RPM's. I would shorten the oil tube as short as I could get it to try to try to prevent the oil from coming up. How far into the crankcase does the PCV tube go, 1/2 inch through the top of the block? Guess it's trial & error????
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Ayr Hed
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Re: PCV

Post by Ayr Hed »

Thanks Brad...QED :tu:
'64 Monza coupe 110/4 spd

64powerglide
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Re: PCV

Post by 64powerglide »

Those carb photo's look like the best way to go. I had a 65 Spitfire with SU's & I put Chrome air cleaners on & on one I drilled the back & put on a 1/4 pipe nipple then a hose to the vented valve cover. About the same thing as those adaptors for the air cleaners in the photo's. Problem solved I would say, at least a good idea of how. :tu:
Brad, I don't know where you find all this info but I know everyone appreciates it. :ty:
64Powerglide, Jeff Phillips

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Re: PCV

Post by bbodie52 »

64powerglide wrote:I would think with the throttle wide open your vacuum would be at maximum in the balance tube but as you said more pressure build up might be more than it can handle even at maximum vacuum. Is it possible to put a vacuum gauge on each inlet & see how much vacuum it has at different RPM's. I would shorten the oil tube as short as I could get it to try to try to prevent the oil from coming up. How far into the crankcase does the PCV tube go, 1/2 inch through the top of the block? Guess it's trial & error????
When your car is idling-whether it's fuel injected or carbureted-the throttle plate or plates are restricting the amount of air the engine can breathe in. The pistons are attempting to "suck" the mixture past the throttle. (Of course, in reality, it is atmospheric pressure that is attempting to "push" air into the engine as the pistons travel downward on their intake strokes.) When throttle is closed, vacuum is high in the intake manifold, from the throttle plate(s) to the combustion chambers. By contrast, at wide open throttle there is relatively little restriction to outside air entering the intake manifold, so vacuum in the manifold is very low.

When you floor the accelerator pedal, you can watch manifold pressure (another word for vacuum) swing from strongly negative to nearly zero (atmospheric pressure). When your engine is "on the overrun," like using engine braking down a steep hill at high RPM, you'll see really high vacuum readings. Naturally, turbocharged and supercharged will show very different results, with readings swinging into the positive at high speed. IAP's vacuum gauge is not designed for turbo or supercharged vehicles. Your vacuum gauge is also a sort of "poor man's" fuel mileage indicator; when vacuum is low, you are burning more fuel.
http://www.international-auto.com/fiat- ... gauges.cfm

On a carbureted engine, manifold vacuum (and vacuum in the Corvair vacuum balance tube) is at its highest when the throttle butterfly valves in the carburetors are closed. High RPM with the throttles closed (as when coasting and decelerating) increases manifold vacuum to the maximum — produced as the pistons attempt to draw in air on the intake stroke at a high RPM with the intake openings closed.

When the throttle is opened, intake manifold vacuum approaches zero. As engine RPM increases with the throttles open, intake air velocity increases as the speeding pistons rapidly pump (draw) more air volume through the carburetor throats. This airflow creates a vacuum within the carburetor restriction (venturi) that draws fuel from the float bowl to mix with the airflow passing through the venturi. The resulting fuel/air mixture feeds each cylinder during the intake stroke, which provides a compressed combustible fuel/air mixture that ignites and produces the power stroke. This is why the above description states "Your vacuum gauge is also a sort of "poor man's" fuel mileage indicator; when vacuum is low, you are burning more fuel. When the throttles are open, vacuum is low, but air velocity is high — drawing in more fuel through the carburetor venturis which increases engine power.

Getting back to the PCV system, it was designed by engineers to deal with crankcase ventilation requirements in a wide range of engine operating conditions — full throttle, closed throttle, partial throttle, high RPM, low RPM, and everything in-between. The baffle plate and vents, the PCV tube, the PCV valve or fixed vacuum orifice that is connected to the vacuum balance tube, and the PCV breather connected to the air cleaner, are all part of a dynamic system design that is intended to function continuously during all engine operating conditions.

Shortening the dipstick tube to prevent oil from being ejected because of excessive crankcase pressure buildup should not be necessary or desirable. Excess crankcase pressure buildup that would force oil out of the dipstick tube is an indicator, or symptom, of either a faulty PCV system and/or excessive piston blowby due to bad rings, pistons, or cylinders. Modifying the dipstick tube does not fix the problem! A compression test or a leakdown test will reveal a faulty piston seal. An inspection of the PCV system would reveal any faults with that system.
Crankcase Cover and Vent
Crankcase Cover and Vent
PCV Tube Connections.jpg
Corvair Crankcase Ventilation (1963-1969) and Turbo
Corvair Crankcase Ventilation (1963-1969) and Turbo
Conclusion

The goal of the Corvair owner is to maintain the PCV system operation originally intended by GM engineers by cleaning the system (PCV Valve or Fixed Orifice) regularly. If the system is modified — as with the installation of custom air cleaners — the original tubing connections must be re-established with the newly installed custom air cleaners to ensure proper operation of the PCV system. A road draft tube is a poor substitute, as would be installing valve cover breathers or an oil filler cap breather. The properly operating PCV system minimizes crankcase contamination caused by normal piston blowby, which helps to prolong the life of the engine and ensure proper operation.
Brad Bodie
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Re: PCV

Post by Spyder4364 »

I have a 64 spyder with a lot of modifications big pistons custom cam 140 heads big wheel on 65 turbo 65 turbo carburetor MSD ignition with electronic boost controller with dash adjustable control.a knock sensor on the dash. If I am not very careful the boost will peg the gauge at 20 psi but is higher than that. I have had problems with oil being blown out the dip stick which I know have controlled with high vacuum in the crank case pulling just before the turbo wheel and thru a oil separator can in line I would like a recommendation for oil and oil volume I have all the Otto pan and valve covers plus a main connector plate so I really don’t know how much oil to put in

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Re: PCV

Post by terribleted »

Stock dipstick? Still needs to be full on the dipstick. add oil until it is at the full mark. If it is empty when you start and you keep track how much you put in you will then know the capacity.
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