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  •  » Got an idea about vacuum advance(which I don't use!)....

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    2/14/2021 6:12 PM  #1

    6sally6
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    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,853

    Got an idea about vacuum advance(which I don't use!)....

    As we all know....vac. advance  tuning is a trial & error process because you can't 'set-it' in the driveway!
    When it is connected to ported vac it works butt....as soon as you give it some gas the vac. advance drops to zero!
    When hooked to mani vacuum the vac. advance is activated all the time.
    What about......................(for guys using ported vac advance)......hook up the vac advance to MANI first and with a vac gauge compare the difference between when the vac hose is plugged off. 
    Make a note of it.......(example  30 degrees)
    THEN.......when you attach the hose to the ported side you will KNOW how much vacuum advance you have!
    At least this will give you a starting point when trying to tune the vacuum advance.
    IF it rattles under acceleration....stop and give the adjustment screw a turn (in the canister)
    6sal6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    2/14/2021 7:38 PM  #2

    MS
    Forum Originator

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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,260

    Re: Got an idea about vacuum advance(which I don't use!)....

    Ported vacuum increases with engine RPM

    Manifold vacuum decreases with engine RPM.

    I think the readings will vary with load.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    2/14/2021 10:15 PM  #3

    Cab4word67
    Senior 24-7 FYI Addict

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    From: Portland, Ore
    Registered: 4/06/2019
    Posts: 1,154

    Re: Got an idea about vacuum advance(which I don't use!)....

    I think when I put my new 289 (aka 297) motor back in and verifie my full advance I will try both ways just to see if the car runs better or worse. When I did my dauthers 63 nova SS 194 six  with a Clifford's intake , holly 2 bl and headers with 40s we ran no advance and the car pulled hard.  

    Slammed Big Blue, ran over the varmints that messed with the Stang. Now all is good in the NW
     

    2/15/2021 10:52 AM  #4

    RV6
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    From: Pine Junction, CO
    Registered: 3/01/2016
    Posts: 1,248

    Re: Got an idea about vacuum advance(which I don't use!)....

    The only difference between ported/manifold advance is when the throttle is closed.

    Last edited by RV6 (2/15/2021 10:54 AM)

    Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
     

    2/15/2021 3:54 PM  #5

    rpm
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    From: Bakersfield, Ca
    Registered: 9/17/2013
    Posts: 3,660

    Re: Got an idea about vacuum advance(which I don't use!)....

    RV6 wrote:

    The only difference between ported/manifold advance is when the throttle is closed.

    Really?
    https://youtu.be/r7ggHhdujj0

    Bob. 69 Mach 1, 393W, SMOD Toploader, Armstrong  steering, factory AC.
     

    2/15/2021 5:54 PM  #6

    RV6
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    From: Pine Junction, CO
    Registered: 3/01/2016
    Posts: 1,248

    Re: Got an idea about vacuum advance(which I don't use!)....

    Bearing Bob wrote:

    RV6 wrote:

    The only difference between ported/manifold advance is when the throttle is closed.

    Really?
    https://youtu.be/r7ggHhdujj0

    Hook two vacuum gauges up, one too ported, one too manifold. Go drive. You'll see the graph above happen in real time. 

    Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
     

    2/15/2021 9:31 PM  #7

    rpm
    Senior 24-7 FYI Addict

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    From: Bakersfield, Ca
    Registered: 9/17/2013
    Posts: 3,660

    Re: Got an idea about vacuum advance(which I don't use!)....

    RV6 wrote:

    Bearing Bob wrote:

    RV6 wrote:

    The only difference between ported/manifold advance is when the throttle is closed.

    Really?
    https://youtu.be/r7ggHhdujj0

    Hook two vacuum gauges up, one too ported, one too manifold. Go drive. You'll see the graph above happen in real time. 

    That ain't gonna happen. Mine, today, right now, runs best without vacuum advance. Tomorrow... who knows

    Bob. 69 Mach 1, 393W, SMOD Toploader, Armstrong  steering, factory AC.
     

    2/16/2021 9:22 AM  #8

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,335

    Re: Got an idea about vacuum advance(which I don't use!)....

    So....at start up which is preferred?

    At normal idle which is preferred?

    And why?

    Last edited by Nos681 (2/16/2021 9:23 AM)

     

    2/16/2021 11:15 AM  #9

    RV6
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    From: Pine Junction, CO
    Registered: 3/01/2016
    Posts: 1,248

    Re: Got an idea about vacuum advance(which I don't use!)....

    Startup: Ported. This is so you would start with just the initial timing. If at 8 BTDC I don't think it would matter, but some run ridiculous numbers (12+) and the added advance from manifold could make starting difficult.
    Idle: Manifold. Lean mixtures take longer to burn and the added advance helps with the burn.

    I run manifold with 12 initial. Seems to run good unless the vacuum can messes up. I have never run ported for a comparison and I should. I would imagine just cruising the difference would be negligible as the vacuum is the same between to two ports when the throttle plates are open.

     

    Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
     

     

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