PCV or Breather caps???

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FlDart360

FlDart360

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The previous owner did away with any type of PCV setup on my 360. In its place are two nice Edelbrock valve covers each with a breather cap. My carburetor is a 670 Holley and my intake is an RPM Air Gap. Just curious does it matter?

Thanks.
 
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Should have one of each. Breather on one side and a pcv tapped into the carb on the other.
 
Yes it matters. Your engine needs a closed crankcase breather system, to continuously get rid of moisture and blow-by gasses. Moisture in the oil pan combines with hydrocarbons to form acids that attack your bearings.
but additionally, every street carb I have ever seen, has a port on it for that system, and the carb is calibrated to be working with that system. This is your idle-air bypass. If you eliminate it, you will have to introduce that idle air somewhere else, usually by increasing the curb-idle opening. This puts your throttle valves too far up the Transfer slots, and makes the engine run rich. In compensation, the mixture screws are screwed in too far, which leans the tip-in, sometimes causing a hesitation. So now everything is all crossed up. In compensation, the timing is advanced, the throttle closed and the mixture screws brought back on line. But with this compensation come two new problems; 1) the power-timing is advanced a like amount, and you may be putting the engine into detonation, and 2) you may put the engine into detonation at any time, any rpm, with just a little too much throttle. Detonation is bad news, usually breaking the pistons or shattering the plugs. The fix for this is running premium fuel, possibly needlessly costing you hundreds of dollars a year.
If you have a performance cam, it often needs all the bypass air you can find. The PCV system is the first and easiest place to go looking for it.
At heavy loads the engine naturally produces more blow-by, and the PCV system gets overloaded. At this time the valve cover breather will work in reverse, as a pressure relief. If it is not plumbed to the airbox, or somewhere else, it will puke oil vapors onto the valve cover and make a mess.
If you are a streeter,on the basis of reducing or eliminating acid formation alone, your engine needs the PCV to be operational.

Ok, I may have exaggerated the carb adjustments a little, but the end result is the same; your streeter needs an operational PCV system.
 
AJ hit the nail on the head. I'll add that instead of an open breather on the side opposite the PCV, an oil separator with a hose fitting should be plumbed to the air cleaner.
 
PCVs work but they also can suck.
The one on my stock 318 works well, the one on my mild bb sucked.
I went with that wagner one, yes more expensive than the parts store one but it has worked extremely well.
I'm no expert on pcvs, but I spent some coin on everything else, and the parts store pcv would suck oil too, and leak on the valve cover.
No more, and it seems to run a bit smoother.
 
AJ/FormS said:
Yes it matters. Your engine needs a closed crankcase breather system, to continuously get rid of moisture and blow-by gasses. Moisture in the oil pan combines with hydrocarbons to form acids that attack your bearings.
but additionally, every street carb I have ever seen, has a port on it for that system, and the carb is calibrated to be working with that system. This is your idle-air bypass. If you eliminate it, you will have to introduce that idle air somewhere else, usually by increasing the curb-idle opening. This puts your throttle valves too far up the Transfer slots, and makes the engine run rich. In compensation, the mixture screws are screwed in too far, which leans the tip-in, sometimes causing a hesitation. So now everything is all crossed up. In compensation, the timing is advanced, the throttle closed and the mixture screws brought back on line. But with this compensation come two new problems; 1) the power-timing is advanced a like amount, and you may be putting the engine into detonation, and 2) you may put the engine into detonation at any time, any rpm, with just a little too much throttle. Detonation is bad news, usually breaking the pistons or shattering the plugs. The fix for this is running premium fuel, possibly needlessly costing you hundreds of dollars a year.
If you have a performance cam, it often needs all the bypass air you can find. The PCV system is the first and easiest place to go looking for it.
At heavy loads the engine naturally produces more blow-by, and the PCV system gets overloaded. At this time the valve cover breather will work in reverse, as a pressure relief. If it is not plumbed to the airbox, or somewhere else, it will puke oil vapors onto the valve cover and make a mess.
If you are a streeter,on the basis of reducing or eliminating acid formation alone, your engine needs the PCV to be operational.

Ok, I may have exaggerated the carb adjustments a little, but the end result is the same; your streeter needs an operational PCV system.
Click to expand...
That basically explains every issue I’m having with my Jeep haha. Guess I should fix that
 
Rebuilt the 2 barrel carb on my 318, kit had a new base gasket so I was very happy as I had to make one at first.

After a few weeks, milky oil, oil pushing out of dipstick at regular intervals, wth?
Ran a little crappy too.

New base gasket was not cut out in center where the pcv port came into the baseplate of carb.

Good thing I check and recheck stuff because I completely missed the carb gasket thing, but when I made that first gasket I was feeling lazy and preferred cutting out one oblong hole instead of two circles.

20181215_194600.jpg
 
I had a Ford 351 4V CJ that I bought very cheep from the owner, he complained that the front and rear intake seals keep blowing out. I took one look and knew what the problem was, he had the stock oil breather cap on one side and had put a spark plug in the PVC hole. No problem at idle but 1st time he revved it the seals would pop out.
 
Update on PCV. Found a nice Edelbrock unit from summit that contains a PCV valve and goes nicely with my valve covers. Thanks to everyone for their input.


IMG_0183.JPG.jpg
 
matthon said:
PCVs work but they also can suck.
The one on my stock 318 works well, the one on my mild bb sucked.
I went with that wagner one, yes more expensive than the parts store one but it has worked extremely well.
I'm no expert on pcvs, but I spent some coin on everything else, and the parts store pcv would suck oil too, and leak on the valve cover.
No more, and it seems to run a bit smoother.
Click to expand...


Sometimes you have to experiment with the parts store units. With patience you find the right one for the application or just get the Wagner unit and have adjustability. I run one off the shelf and it is not sucking oil up, “course the baffles in your cover are just as important as well”!
 
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Baffles? We don't need no stinking baffles!
 
130 dollar PVC valve......with available add ons. That's just funny right there.
 
Glad you got it in OP; a wise move. Now.... did the engine's idle change and need significant re-adjustment after the PCV was put in? Is there any new hesitation when you first lightly open the throttle? And have you measured the vacuum in the intake at idle?

The reason to ask is that ALL PCV's are dual flow units. There is a low flow level for when the engine is at idle and other low engine airflow situations like mild cruising and tooling around town, and a high flow level for heavy cruising, going up hills, WOT, etc. These 2 flow levels generally reflect the load on the engine, and the trigger for the PCV valve to change from low to high flow level is the vacuum level under the carb, in the intake manifold. If you have a cam that idles rough, generally the idle vacuum level will be low, and stock type PCV valve will open up to the high flow level at idle. That will throw off carb adjustments in the areas discussed in post #4.

In that case, you don't want a stock PCV but one that has the flow level transition at a lower manifold vacuum level. You can find some from the parts stores, as suggested in post #12, or use an adjustable one; and MP has one for stock valve covers. I can't find any info on the one you have as for the transition vacuum level.

So if the engine's idle and off-idle throttle response has changed for the worse, then you may have some further measurements and adjustments to make.
 
I’d use or reinstall the valve cover breather and PVC for a street or light street strip car. If your car is mostly to fully a race car, then I’d run just breather on the valve covers or a e-vac system into the header collector.
 
nm9stheham said:
Glad you got it in OP; a wise move. Now.... did the engine's idle change and need significant re-adjustment after the PCV was put in? Is there any new hesitation when you first lightly open the throttle? And have you measured the vacuum in the intake at idle?

The reason to ask is that ALL PCV's are dual flow units. There is a low flow level for when the engine is at idle and other low engine airflow situations like mild cruising and tooling around town, and a high flow level for heavy cruising, going up hills, WOT, etc. These 2 flow levels generally reflect the load on the engine, and the trigger for the PCV valve to change from low to high flow level is the vacuum level under the carb, in the intake manifold. If you have a cam that idles rough, generally the idle vacuum level will be low, and stock type PCV valve will open up to the high flow level at idle. That will throw off carb adjustments in the areas discussed in post #4.

In that case, you don't want a stock PCV but one that has the flow level transition at a lower manifold vacuum level. You can find some from the parts stores, as suggested in post #12, or use an adjustable one; and MP has one for stock valve covers. I can't find any info on the one you have as for the transition vacuum level.

So if the engine's idle and off-idle throttle response has changed for the worse, then you may have some further measurements and adjustments to make.
Click to expand...


The most obvious thing was about a 200 RPM increase at idle. I adjusted the idle screw to take care of that but haven’t road tested yet. I haven’t had any issues with hesitation to contend with before so I hopeful this won’t upset things too much. Will try latter today to get some test and tune time after completing some honey-dos.
 
Wonderful Hot Rod !

In defense of the previous owner, he may have read an article from Hot Rod.
Quote:
Venting a typical V-8 engine isn’t a complex affair. A breather atop each valve cover is usually all that’s needed. Of course, replacing one with a PCV valve to introduce a bit of vacuum into the system and to redistribute the unburned hydrocarbons back into the engine via the carburetor or throttle body yields a cleaner and much more environmentally friendly solution.
 
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