Riddle me this..mechanical vs vacuum advance

Small Block Mopar Engine

  1. Challngd73

    Challngd73 Well-Known Member

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    Ok so I have another thread in here about troubles with my La based 408 stroker having troubles staying running in gear at low rpm, and what appears to be a fouling issue of the plugs. It’s a blueprint 408, that I bought never run, from a 3rd party. The tech from blueprint got back to me with some inquiries I had about the motor build, and in his response he said “timing needs to be mechanical only, no vacuum advanced used.”
    When I got my motor, it has an msd distributor in it with vacuum advance and that is always how we have tried to time it. I’m assuming the shop I bought this motor from added the msd vacuum advance distributor. Would running vacuum advance and trying to time the motor with it cause any of my issues? Sorry if it is a dumb question, as any old car I have ever had, they all had vacuum advance.
     
  2. toolmanmike

    toolmanmike Moderator Staff Member FABO Gold Member

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    No vacuum advance to help prevent detonation I bet.
     
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    • halifaxhops

      halifaxhops It's going to get stupid around here! FABO Gold Member

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      Really depends can you call me I will pm you my number.
      Hoppy
       
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      • halifaxhops

        halifaxhops It's going to get stupid around here! FABO Gold Member

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        Thats what I am thinking and easier starts also, I have to talk to him. @Johnny Mac One of yours?
         
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        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          I would think that with the large amount of bolt on’s to that long block- mechanical advance is a way to lower the variables.
          With that said- is the cam so radical that this motor has low vacuum?
           
          Last edited: Sep 17, 2021
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          • halifaxhops

            halifaxhops It's going to get stupid around here! FABO Gold Member

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            I agree, tons of variables there.
             
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            • Challngd73

              Challngd73 Well-Known Member

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              Adv duration on cam is 285 int/297 exh
              .545 int/.545 exh, .241 int/.247 exh @ .050 with 110 Lsa. Mechanical flat tappet. Hoppy I’ll call as soon as I can, I just got this Info and I’m driving to PA for the RV show with the mrs.
               
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              • halifaxhops

                halifaxhops It's going to get stupid around here! FABO Gold Member

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                Where the farm show?
                 
              • Challngd73

                Challngd73 Well-Known Member

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                RV show in Hershey PA.
                 
              • halifaxhops

                halifaxhops It's going to get stupid around here! FABO Gold Member

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                I am NW of there prob 40 miles, was just wondering.
                 
              • Challngd73

                Challngd73 Well-Known Member

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                Wow probably will drive right by you. Driving down from Rochester NY.
                 
              • halifaxhops

                halifaxhops It's going to get stupid around here! FABO Gold Member

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                I am kind of off 322.
                 
              • TT5.9mag

                TT5.9mag Two atmospheres are better than one

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                You can run vacuum advance on anything. As long as you TUNE it to the engine. On a street driven car it will be beneficial while cruising. Tuning the initial, the curve, and the mechanical for total timing is the same with or without the vacuum can. And should be done with the can disconnected and the hose plugged.
                 
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                • Bewy

                  Bewy Well-Known Member

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                  There is no 'riddle' about vac adv v mech advance. They do different things, work differently, but both change the ign timing. Bit like a cam & headers: different things, but both can add power to the engine.
                  From the specs that you provided, this engine is going to like a lot of timing at idle. Maybe as much as 30+ degrees.
                  Chrysler rarely made mistakes, but they did by not using manifold sourced vac adv MVA ]. They used the useless ported vac adv. MVA does everything PVA
                   
                • Bewy

                  Bewy Well-Known Member

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