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Technical How do breathers work?

Discussion in 'The Hokey Ass Message Board' started by flypa38, Feb 12, 2016.

  1. flypa38
    Joined: May 3, 2005
    Posts: 529

    flypa38
    Member

    Ok...maybe a bad thread title for what Im asking.....I understand their function.
    Thinking of making some custom calve cover breathers using some perforated stainless around the sides to match my air cleaner. Seems like all the ones I've seen are vented toward the valve cover though. Is there a reason venting out the sides would be no good?
    Secondly, what would be good to use inside? I might just cut up some cheap chrome ones and use everything but the tops.
    If it matters, it's on a '56 316 Pontiac wit California Custom valve covers and a road draft tube.
    Thanks for any insight!
    Johnny
     
  2. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,553

    Ebbsspeed
    ALLIANCE MEMBER

    It shouldn't matter which side of the breather draws in the air.

    Does this motor still have the draft tube system on it, or has it been changed to a PCV type setup?
     
  3. flypa38
    Joined: May 3, 2005
    Posts: 529

    flypa38
    Member

    Road draft tube.
     
  4. ghornbostel
    Joined: Jan 3, 2012
    Posts: 131

    ghornbostel
    Member

    this is where mine ended up. Started out just screwing filtered caps on the valve covers but they dripped on the valve covers. Happened to see a set of NASCAR type and they looked to be about 3" in height above the covers. Seems to keep the splashing oil in the valve covers from going out the breathers without an elaborate baffle in the tube. The are Ford truck breathers and fit on a taper. The tube at the rear of the right hand air cleaner draws from the crankcase through the stock PCV. There is a breather on each valve cover.


    000_1011.JPG
     
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  5. Is there enough vacuum at the top of the air cleaner to put the crankcase under a slight vacuum? :confused: I would have thought that you'd want a vacuum source somewhere below the throttle plates.
     
  6. ghornbostel
    Joined: Jan 3, 2012
    Posts: 131

    ghornbostel
    Member

    The more important part to me is that the air drawn into the crankcase is filtered by the breathers. I didn't want to draw vacuum from a area that couldn't be satisfied as the breathers will not allow the crankcase to hold a vacuum. The way I see it is it seems to keep the oil mist off the valve covers and engine compartment that you can't control from coming out of the breathers. But then I'm not sure I understand everything I know about it.
     
  7. Well if it keeps oil from collecting in the breathers it must be working at least to some degree. But the way it seems to be laid out in your picture left me scratching my head a bit. When I picture a PCV system I think of something that's plumbed up more like this. You're right to want only filtered air to be drawn into the crankcase, but that's usually done with either a filtered breather cap or a small breather filter inside the air cleaner.

    [​IMG]
     
  8. sunbeam
    Joined: Oct 22, 2010
    Posts: 3,925

    sunbeam
    Member

    There are 2 types of PVC systems type 1 uses a pvc valve and a vented breather works well when there is high vacuum. Not is good at wide open throttle. Type 2 has the breather vented to the air cleaner using the suction from the carb at wide open throttle.
     
  9. ghornbostel
    Joined: Jan 3, 2012
    Posts: 131

    ghornbostel
    Member

    The way my engine is set up it doesn't have positive crankcase ventilation. My oil filler caps are open with a filter inside the caps. The crankcase is open to the atmosphere. It is basically a pre PVC engine, the difference being that it doesn't have a breather pipe going from the crankcase to the bottom side of the chassis. The breather pipe is going to the air intake side of the carburators. I just don't want the byproducts of that crankcase all over the bottom of my chassis. Instead I burn them in the engine and send them out the exhaust pipe. Hope this clears that up as I was probably much to vague about what I had done. What sunbeam says above is exactly what happens when you draw vacuum at the manifold at open throttle.
     
  10. Thanks for the follow-up. ;) I just hadn't really studied a vent system laid out this way before. And from the picture posted I wasn't 100% sure how everything was routed. Does the pipe in the air cleaner stop flush or near flush to the top, or is it routed down closer to the top of the throttle bore?
     
  11. ghornbostel
    Joined: Jan 3, 2012
    Posts: 131

    ghornbostel
    Member

    The carbs are 3c IDA Webers. The tube is at the outside edge of the velocity stack of that choke. I felt that the air velocity would be the greatest at that point. The tube is flush with the back side of the cover. I kinda screwed the attachments up but you get the picture.

    000_1062.JPG 000_1062.JPG 000_1057.JPG




     

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  12. That's just a great lookin' engine. :cool: Looks like something from an old CanAm racer. :D
     
  13. ghornbostel
    Joined: Jan 3, 2012
    Posts: 131

    ghornbostel
    Member

    Thanks. Its 39 years of evolvement.
     
  14. flypa38
    Joined: May 3, 2005
    Posts: 529

    flypa38
    Member

    So will what I was planning work ok? Only difference between what I wanted to do and stock is that the filtered breather caps will be open at the sides instead of toward the valve cover. If not maybe a black solid underlay beneath the perforated stainless sheet.
    Without opening up my original breather caps, would they have been baffled to cut down on oil mist? Seems like the valve covers have some oil on them now with the cheapo chrome caps as compared to when I had the originals installed. Actually was worse when I converted to PCV, but I put the road draft tube back in anyhow so that's no longer a factor.
    Again, what would be a good filter media to use? Foam of some kind, brass wool, etc?
    I just can't find anything I like with the cal custom valve covers.......
    Thanks fellas.
    Johnny
     
  15. Sorry for kind of taking your OP off topic... :oops:

    Venting the breather caps from the sides should work OK, theoretically. The only issue you might run into is the air flow over that area of the engine at speed and with the cooling fan moving air over the valve covers. I suppose there's a slight chance of creating a low pressure area (slight vacuum) around the breathers and this might tend to try drawing oil and crankcase vapors out of the breathers.


    Either way you probably want some kind of baffling in the valve covers or breathers to keep any oil spray out of the caps. Brass wool should work fine for a filtering element, or maybe some material like whatever they call that stuff that Scotchbrite pads are made of. o_O
     

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