To Vacuum Advance or Not to Vacuum Advance

Fuel and Air Systems

  1. mopardude318

    mopardude318 Well-Known Member

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    Wow... you guys really got me wanting to change my mechanical advanced MSD distributor to a vacuum advance one. Had no idea there were that many benefits. Lol.

    Now the question is which one do I run for an aluminum head, large cammed hydraulic roller 408? And what would be compatible with my MSD Digital 6+ ignition box?
     
  2. 512Stroker

    512Stroker We are all here because we are not all there.

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    That is what I did, got rid of my MSD for a FBO distributor. Give Don a call at FBO he will curve one for your engine. The distributor he did for me with a vacuum advance ran great out of the box. I do believe you can run your MSD box just make sure you ask him for the correct cap so you can keep your current spark plug wires.
     
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    • mbaird

      mbaird mbaird FABO Gold Member

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      I found a youtube vid of a vacuum gauge thru the 1/4 and the vacuum built as RPMs built thru each gear and was up to 6”s as he
      ran thru the traps .

      I will try to find and link it.
       
    • yellow rose

      yellow rose Doctor of Thinkology.

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      What????? That means the carb was too small. Or something was seriously wackadooooooooo.
       
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        I'ma thinking it was calibrated in something other than vacuum
         
      • mbaird

        mbaird mbaird FABO Gold Member

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        It was a vacuum gauge.
        . It may have been due to a restriction such as a small carb. But most of us run a carb smaller than the max the engine can handle on our street/ strip cars.
         
      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        reads more like CC-pressure. If you find it, I'd like to see that phenomenon.
         
      • mbaird

        mbaird mbaird FABO Gold Member

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        image.jpg

        I can find it on my smart TV in youtube but not on my phone to attach the link.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        That or restricted intake class.
        I always think circle track for running restrictor plates or spec'd 2 bbl carbs, but could be drag racing too.
        There are (or were) some NHRA stock classes where 2 bbl 273 B-bodies fit in. R Stock, T Stock? Something like that. A coworker and somewhat of a mentor when I first got into this stuff had run in it. Claimed to have held the national record for a while, and I believe he did.
         
      • mbaird

        mbaird mbaird FABO Gold Member

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        Here is 3rd gear...
        image.jpg
         
      • mbaird

        mbaird mbaird FABO Gold Member

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        He had his foot into it for 10secs so it was a fairly fast car.
         
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        • mbaird

          mbaird mbaird FABO Gold Member

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          The whole point of this is... can Vac Adv help in dragracing ? And I think that with many Non Maxxed out street/strip cars it very possibly could.
           
        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          Its definately worth the discussion and investigating. I need to pencil in trip to a drag strip. I was planning to go when my mechanic gets his Omni done. That will be with a 3310 '750' frankencarb on a 340. But after that, I have a 650 vac secondary that I want to retry. So that would be a pretty good typical enthusiast carb/engine combo.

          Can't help on the youtube link. Simple code like Html or I get lost.
          Any other info on the car? Little air cleaners?
           
        • mbaird

          mbaird mbaird FABO Gold Member

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          That was the only shot in that Video. He has others and it might be a Mopar he is running. Maybe a Magnum?
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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          Wait; it idles at like 2" vacuum, and when he shuts it off, it's still at 2" vacuum. I'm skeptical as to what that gauge is actually measuring; I mean where. It doesn't seem to be intake manifold vacuum; the gauge acts more like it's hooked to a cc evacuator system, or IDK the fresh-air intake, ahead of the supercharger.. IDK but I doubt it idles at 2 inches
           
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          • mbaird

            mbaird mbaird FABO Gold Member

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            I was thinking it might be hooked to ported vacuum and the needle was resting until he hit the throttle. But something does seam off about it.
            Someone needs to video their gauge.
             
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            • mderoy340

              mderoy340 Well-Known Member

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              My 340 immediately goes to zero and stays there until I lift. I run vac on ported and leave it hooked up at the track. 9" at idle in gear, 11" at 2k launch, vcan set to move at 10"
               
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