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Thread: pcv or evac:which is better for drawing vaccum?

  1. #1
    Senior Member EXPERT BUILDER
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    pcv or evac:which is better for drawing vaccum?

    pcv from valve cover to intake or evac from collector to valve cover....what are the diffrences on a bbc with a single plane,dominator set up with a plate.my exhaust is free flowing(no chambered mufflers).



    goal: to make cheap mans vacuum pump.....ideas???comments???thx in advance!

  2. #2
    Senior Member MASTER BUILDER
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    at WOT I would think header collector to valve cover would give more vacume. pretty much the same as how a carb works with Bernollis principle.

    edit, at idle a pcv probably draws more vacume.

  3. #3
    Has anybody tried electric vacuum pumps? There's a guy on RJ selling them for $160. Unless I come across a deal at a swap meet for a mech. pump I will be running the valve cover to collector. I have a motor plate that might make mounting the mech pump a challenge.

  4. #4
    Senior Member RACING JUNKIE
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    Moroso makes a evac kit for about $40 Its the valve cover to collector type, works great at WOT which is when you need it most.
    ><Cp
    ***IN GOD WE TRUST***

  5. #5
    Senior Member DYNO OPERATOR
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    Use both at the same time.

    By theory when one is open the other will be closed.

    PCV is open only at times of high vacuum. Pcv is closed during full throttle. Crank evac system is mostly closed at high vacuum and is open when at low vacuum.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  6. #6
    Junior Member APPRENTICE
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    This is the exaust setup I have:

    Long tube headers > 3"-2.5" reducer > 2.5" H pipe > 2.5" delta 40's with 3" pipes going all the way back.

    Now lets say I properly installed the collector evac kit and ran both of them to one valve cover and the other valve cover would have a hose running directly to intake vac. Does that seem ok?

    Should I add a pcv valve, seporator, one way check valve?

    http://www.racingjunk.com/gallery/profile/255255

  7. #7
    Senior Member RACING JUNKIE
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    Quote Originally Posted by edvancedengines
    Use both at the same time.

    By theory when one is open the other will be closed.

    PCV is open only at times of high vacuum. Pcv is closed during full throttle. Crank evac system is mostly closed at high vacuum and is open when at low vacuum.

    Ed
    How would you go about plumbing in a setup like that.To pull off one v/c with a pcv,doesn't the other have to have a breather so that it draws thru the engine?Looks like you would need 4 breather holes that way.Not trying to dispite you,just honestly curious.
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  8. #8
    Senior Member RACING JUNKIE
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    The only thing I dont like about a pcv system is the oil vapors that are pulled into the intake plenum and intake ports valves etc, which leave nasty flow inhibiting deposits. Rather crap that junk out my exhaust and say adious.......
    ><Cp
    ***IN GOD WE TRUST***

  9. #9
    Senior Member EXPERT BUILDER
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    i kinda agree with suckin into the intake tract oily fumes is kinda icky-is it a concern? if not,where to plumb into on my dart tall deck intake?by the way ive also got a nitrous plate kit on...what is opinions of electric vacuum pumps?if i just run evac to header is it ok to just use one valve cover lined down to one collector(cause i have air to fuel ratio sensor welded in one collector already)

  10. #10
    Junior Member APPRENTICE
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    :idea: So when is someone going to step up to the plate and get a patent on a AFFORDABLE electric or belt drive evac pump for the high performance street guys and become a multi millionaire?

    I would do it but I dont have the funds to get it started


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