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Technical You guys have an answer?

Discussion in 'The Hokey Ass Message Board' started by Ghost28, Apr 16, 2014.

  1. Ghost28
    Joined: Nov 23, 2008
    Posts: 3,154

    Ghost28
    Member

    I picked up a small block chevy the other day. It has a performer aluminum manifold on it, when I pulled the carb off and looked over the manifold it had two 3/8th inch holes drilled into it under the carb into the oil valley area. Would this be done to reduce the vacuum pressure in the engine?
    John
     
    Last edited: Apr 19, 2014
  2. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,830

    Mike51Merc
    Member

    Possible homemade pcv system. Vacuum pressure "lives" in the intake passages, not in the crankcase.
     
  3. onetrickpony
    Joined: Sep 21, 2010
    Posts: 427

    onetrickpony
    Member
    from Texas

    You sure those holes go all the way to the crankcase? I've seen something similar but it went into the exhaust crossover as part of the EGR.
     
  4. NMCarNut
    Joined: Nov 28, 2009
    Posts: 630

    NMCarNut
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    Is vacuum pressure equivalent to suck blow?

    As stated this might be an attempt at a pcv system, but a rather piss poor one in that it has no regulation (other than the hole size) and no oil separation from the fumes.

    Plug the holes and install a proper system.
     
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  5. onetrickpony
    Joined: Sep 21, 2010
    Posts: 427

    onetrickpony
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    from Texas

  6. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,830

    Mike51Merc
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  7. Ghost28
    Joined: Nov 23, 2008
    Posts: 3,154

    Ghost28
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    They apear to be cast into the manifold rather than drilled and they don't go all the way to the oil valley. I guess they are factory holes.
     

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  8. onetrickpony
    Joined: Sep 21, 2010
    Posts: 427

    onetrickpony
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    from Texas

    The passage from the head is blocked at the pad where the EGR valve mounts. EGR valve sits beside the carb and meters the exhaust to those two holes.
     
  9. I have never seen that before!! Maybe edelbrock could give you a answer, or shed some light on these holes?
     
  10. Ghost28
    Joined: Nov 23, 2008
    Posts: 3,154

    Ghost28
    Member

    This sounds like a good answer...Thanks
     
  11. NMCarNut
    Joined: Nov 28, 2009
    Posts: 630

    NMCarNut
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    Learn something new every day. Unless you need EGR to pass emissions I'd still block 'em.
     
  12. "50 state street legal means more sales"
     
  13. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    had to have them on post 76 cars here in Illinois if they pulled a visual exam ( which was rare but it has happened in the past) . we ussually plated the egr over after testing and reset the timing back .
     
  14. King ford
    Joined: Mar 18, 2013
    Posts: 1,347

    King ford
    ALLIANCE MEMBER
    from 08302

    Maybe hidden nitrous injection
     
  15. droppedstepside
    Joined: Feb 6, 2009
    Posts: 37

    droppedstepside
    Member
    from new jersey

    I was thinking a hidden nitrous system as well.
     
  16. Bigchuck
    Joined: Oct 23, 2007
    Posts: 1,139

    Bigchuck
    Member
    from Austin, TX

    Just what is "vacuum pressure"? Vacuum is the absence of pressure.
     
  17. vacuum pressure would be suction.
     
  18. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,830

    Mike51Merc
    Member

    Vacuum is negative pressure, but pressure nonetheless.



    Posted using the Full Custom H.A.M.B. App!
     
  19. Atwater Mike
    Joined: May 31, 2002
    Posts: 10,086

    Atwater Mike
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    'Blow' is only an expression...(!)

    ...And AMEN to a non-regulated re-circulatory moving of C/O. Positive Crankcase Ventilation was always regulated through a valve!
     
  20. krooser
    Joined: Jul 25, 2004
    Posts: 4,585

    krooser
    Member

    Got the same holes in my SBO intake…I welded up the EGR deal.
     
  21. Commish
    Joined: Jan 9, 2010
    Posts: 379

    Commish
    Member
    from NW Ok

    Vacuum is negative from 0 PSI, but it is not pressure.
     
  22. loudbang
    Joined: Jul 23, 2013
    Posts: 29,116

    loudbang
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    Vacuum is any LESS pressure than the pressure being introduced to to area.
     
  23. 48FordFanatic
    Joined: Feb 26, 2011
    Posts: 1,336

    48FordFanatic
    Member
    from Maine

    It depends on your reference point you use 14.7 ( atmospheric ) or absolute .
     
  24. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,830

    Mike51Merc
    Member

    Vacuum has many different definitions and so does pressure.

    Vacuum (used in the automotive sense) is pressure. When we say Vacuum we mean suction as in negative pressure pulling atmospheric pressure in. Saying there's no such thing as negative pressure is like saying there's no such thing as negative gravity. An astrophysicist may say there's no such thing as negative gravity, but don't tell that to an aeronautical engineer or the designer of a rollercoaster.

    Absence of pressure is equilibrium. No suck, no blow. No pressure, no vacuum. You can't say that a strong vacuum is a big absence of pressure.
     
  25. loudbang
    Joined: Jul 23, 2013
    Posts: 29,116

    loudbang
    Member

    Ah no the higher pressure is pushing itself into the area of low pressure there is no suck. :p
     

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