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Old 10-22-2010, 12:27 PM
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PCV question

Is there an advantage to running a hose from the valve cover to the carb? I know there needs to be crankcase ventilation. My question is, could I just vent it to the air, or leave it as is? Is there any advantage to either?
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Old 10-22-2010, 01:49 PM
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What you are doing is burning the gases that have been built up in the crankcase. You aren't going to make any more HP but you will be polluting less.
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Old 10-22-2010, 02:09 PM
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The PCV valve needs manifold vacuum to operate, so one end goes in the valve cover and the other end of the valve has a hose to manifold vacuum. There needs to be an air inlet somewhere else. This wants to be filtered air so you don't suck sand and dust into the engine. The factory ran a hose from the other valve cover to the air cleaner housing as a source of filtered air. Alternately, you can use a breather with a filter on the valve cover or oil fill tube.
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Old 10-22-2010, 02:20 PM
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Alternately, you can use a breather with a filter on the valve cover or oil fill tube.

Yes, this is what I have set up on the other valve cover. I asked this question, because I have some hotrod buddies telling me, to just vent to the atmosphere so the valvetrain gases don't get sucked into the intake.
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Old 10-22-2010, 07:04 PM
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Here click the link and you can reads as much as you want to about pcv PCV setup SBC. . And my personnel experience the breathers you use on the valve covers without a pcv not a very good idea . JMO They are better then nothing but you really do need the pcv to be correct and get the benefit's from it. Again JMO I have ran both ways.



Cole
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Old 10-22-2010, 07:23 PM
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Being 58 years old I remember when engines did not have PCV and those engines were much messier along with the engine compartments due to all the oil vapors just blowing around instead of being burned . The PCV system doesn't make an engine run any worse than it would without it and it keeps the engine and engine bay cleaner so why would you want to eliminate it ?
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Old 10-22-2010, 07:25 PM
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Quote:
Originally Posted by adantessr
Being 58 years old I remember when engines did not have PCV and those engines were much messier along with the engine compartments due to all the oil vapors just blowing around instead of being burned . The PCV system doesn't make an engine run any worse than it would without it and it keeps the engine and engine bay cleaner so why would you want to eliminate it ?
Exactly this is so true.


Cole
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Old 12-20-2010, 06:16 PM
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This is the issue Im having, My engine bay gets oily and messy. Was wondering the same thing.
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Old 12-20-2010, 06:44 PM
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The old engines before PCV valves did not just use a breather cap and that does not work very well, you will get moisture and crud accumulation if that is all you have. If you rely on just a cap on the valve cover it will take a slight crankcase pressure to force out the blow-by gasses so it will not do so very well and and as pointed out it will get messy, very messy! The older cars from years ago had a vent tube that came out and ran down the back of the engine, this tube had the end cut at an angle so that while driving the air passing over it created a slight vacuum from the venturi effect. This did work quite well as far as sucking out the gasses, moisture, etc but it was very polluting and it did make a mess under the car and around the back of the engine.
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Old 12-20-2010, 08:29 PM
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Quote:
Originally Posted by oldred
The old engines before PCV valves did not just use a breather cap and that does not work very well, you will get moisture and crud accumulation if that is all you have. If you rely on just a cap on the valve cover it will take a slight crankcase pressure to force out the blow-by gasses so it will not do so very well and and as pointed out it will get messy, very messy! The older cars from years ago had a vent tube that came out and ran down the back of the engine, this tube had the end cut at an angle so that while driving the air passing over it created a slight vacuum from the venturi effect. This did work quite well as far as sucking out the gasses, moisture, etc but it was very polluting and it did make a mess under the car and around the back of the engine.
Ok, so whats the solution?
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Old 12-20-2010, 08:41 PM
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Quote:
Originally Posted by Dajerseyrat
Ok, so whats the solution?


A pcv valve.

The old vent tube would hardly be a good solution even if one could be rigged up, those old engines that had them usually had a port in the back of the intake or even the block for the tube. The tube had a wire mesh strainer type gadget on the end that went into the engine but the other end just had that angle cut and went down into the airstream under the car. Why do you not want to install a PCV valve? They work quite well and are easy to install even if you don't have any of the plumbing there, quite simple really. That breather cap on the valve covers or oil filler tube on those old engines that some people sometimes thought was to vent gasses was actually to filter air being sucked into the engine from the vacuum created by the vent tube. The idea that these breathers were the vents came about because the only time the vent tube worked was when the car was moving along at a pretty good speed, at low speeds or idle there was no vacuum at all and gasses could actually vent out the breather cap during that time. If the tube became clogged which happened all too often then oil and gasses would indeed be forced out these breather caps creating a real mess and causing poor engine ventilation, when all was working properly however these breather caps were to filter incoming air and not to vent the crancase.

Last edited by oldred; 12-20-2010 at 08:55 PM.
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Old 12-21-2010, 09:16 AM
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The solution is quit listening to those so called hotrod buddies and install a PCV valve system.

Vince
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Old 12-21-2010, 10:55 AM
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Quote:
Originally Posted by 302 Z28
The solution is quit listening to those so called hotrod buddies and install a PCV valve system. Vince
I concur - go with the closed PCV system.
There's no shame in adapting newer technology to an old problem.
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Old 12-21-2010, 10:59 AM
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Quote:
Originally Posted by 302 Z28
The solution is quit listening to those so called hotrod buddies and install a PCV valve system.

Vince
Sounds good, however I am unsure of the proper routing, any diagrams or pictures would help greatly.
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Old 12-21-2010, 11:22 AM
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The plumbing is simple and you won't need the hose from the air cleaner to the valve cover for the filtered air going into the engine, just use the breather cap you already have on the valve cover if it is a filter type-if not replace it with one that is. As for the PCV plumbing you just need a rubber grommet for it to fit in for the other valve cover, these can be found in various size combos at Advance, Auto Zone, Oreilly's, etc on the rack they have for specialized parts like door handles and other odd parts. Then all you need to do is to install the PCV valve and grommet into the valve cover and run a vacuum hose to a manifold vacuum source with 1/4" or larger vacuum hose, find a manifold vacuum port that the line fits and you will have it.



Those guys who are just using a breather cap to vent their crankcase have a really poor ventilation system that is hardly working at all. Their thinking is that it worked ok years ago but by just having the breather cap without that vent tube they have the equivalent of the old system with the vent tube clogged! Basically just having breather caps without also having that vent tube properly placed won't work for squat and don't let your buddies tell you otherwise.

Last edited by oldred; 12-21-2010 at 11:32 AM.
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