vacuum advance question

Electrical and Ignition

  1. mopowers

    mopowers Well-Known Member

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    Does anyone have a part number or stock application for an adjustable small block vacuum advance pot? Thanks!

    Also, is there a way you can tell by looking at aftermarket replacements if they are adjustable? Like this one-

    BWD V194 - Vacuum Control | O'Reilly Auto Parts

    v194_primary.jpg
     
    Last edited: Oct 20, 2016
  2. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    Since part numbers varied per application (even smog equipped per state) I would have to say there is no specific single part number for a small block.
    The only real way I know if a can is adjustable is if it is advertised as such or has the allen screw inside the port.

    Take a 3/32 allen wrench to the store with you. :D
     
    Last edited: Oct 20, 2016
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    • mopowers

      mopowers Well-Known Member

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      Did adjustable cans ever come stock on electronic small block distributors?
       
    • TrailBeast

      TrailBeast AKA Mopars4us on Youtube

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      That one I don't know for sure, but I can tell you that most all the old ones I have seen don't.
      When I was looking for an adjustable no one could tell me if what they had was or wasn't so I had to determine that for myself when I went to get it.
      They had a specific part number for the make and model/engine and per any smog states, but nothing about being adjustable unless it was an aftermarket seller like Jegs or Summit.
      I sell advance modified Mopar small block reman distributors and they all come with adjustable before I advance mod them with springs and the FBO limiter plates.
       
    • mopowers

      mopowers Well-Known Member

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      Yeah, I hear ya. I just try to gather as much info, part numbers, etc. before I got to the auto parts stores. Relying on them for that info is, well... You know how that goes. Anyhow thanks for the info.

      I have read online that if the cannister has the hex shape on it, that it's adjustable. I'm not sure how much truth there is to that though.
       
    • TrailBeast

      TrailBeast AKA Mopars4us on Youtube

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      Hm, I'll have to check into that more.
      I do the same with parts and stores because I do totally know how that goes. :D
       
    • mopowers

      mopowers Well-Known Member

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      Well, I emailed the manufacturer about the one in the link and here is what they had to say-

      "Our BWD V194 is not technically adjustable. There is an Allen screw inside the vacuum port, but it is factory set, and has Loctite on it. You would have to adjust it at your own risk, and will need to add Loctite to maintain position. We do not recommend this. Unfortunately, we do not offer an adjustable model for this vehicle. Sorry we couldn’t be of more assistance."
       
    • Yote

      Yote Well-Known Member

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      How would one go about setting an adjustable vac can properly? I understand about the Allen screw location just not sure what I would be looking to achieve in adjustment .
      Yote
       
    • TrailBeast

      TrailBeast AKA Mopars4us on Youtube

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      The basics are that you want as much timing in mid throttle cruise as you can get without pinging.
      Boy, that was a lot easier and faster to say than it is to do. :D

      For example: My own engine runs as high as 52 degrees in the mid light throttle range.
      You can do this because the less load there is on the engine means the timing can be higher during that light load, but as load goes up so does cylinder pressure and therefor preignition can happen sooner as it climbs.
      That is why cars with say 12:1 compression have to use higher octane fuel.
      (Octane raises the detonation point of fuel) so the higher the octane rating the more compression you can run because the pressure and heat in a cylinder can cause fuel to ignite without any spark at all.

      This is how diesel engines work, by compressing the fuel to the point it explodes without a spark at all.
       
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      • mderoy340

        mderoy340 Well-Known Member

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        Standard VC189 is adjustable and has 22* at the crank. Fits OEM electronic dist.
        https://www.summitracing.com/parts/smp-vc189

        Every can I've had with the hex on the end was adjustable.
        Adjusting only changes the amount of vacuum (rate) the advance starts. CCW raises inches of vac to move and CW lowers inch of vac to move. Linkage has a number stamped on it and this would be the number of degrees the can has in distributor degrees. The VC189 is marked 11R and gives you 22 at the crank.

        To limit the max advance you can mod your distributor by adding a 4-40 machine screw to limit max advance where you want it. See picture.

        Someone else may chime in with a part # for an 8.5* can which would give you 17* at the crank. They used to make them but I don't have the part #.

        dist mod 002.JPG
         
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        • RustyRatRod

          RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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          Exactly as above ^^^^^^ the cans with the hex are all adjustable, while the cans that lack the hex are non adjustable.
           
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          • AJ/FormS

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

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            Kudus to you for figuring out how to make that can work!

            I myself run a minimum of 44*@2000, on account of I have overdrive,heehee; with an additional 8 available, but seldom used, through the Jacob's dial-back. So up to 52 it is;imagine that!

            https://www.summitracing.com/parts/smp-vc189
            I was unable to verify that this is a 22* can in the advertising. But if it is 11 on the arm, then it is the same as what I have,indeed a 22* can; nice homework , mderoy.
             
            Last edited: Oct 20, 2016
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            • RustyRatRod

              RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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              If you read the MP engine book, it clearly says that up to and a little over 60* part throttle is normal with a hot street engine. It's all in what combo you have.
               
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              • AJ/FormS

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

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                Thx Rusty, I did not know this, and I have the book,somewhere......lol

                I tried up to 64* or so, but with my 10.7 SCR, and tight squish aluminum heads, I found no advantage.
                The dial-back allows me to add timing from the cab. My usual method of determining the optimum cruise advance, is to travel a known route 13 miles long that is dead-flat. I run it with the timing set at a baseline, and a throttle stop that allows a repeatable butterfly angle. Then I add 3 degrees and watch the speedo and tach. If speed goes up,I repeat. And so on until speed plateaus.
                With my overdrive, 60 MPH is 2064rpm, and 44 was the magic number. In direct the tach jumps to 2650, and the timing jumps to 49*.
                The maximum mechanical advance I run is 34* at 3400, to which the Vcan adds 22* for a total of 56*; and to that I could add 8*;so a grand total of 64*. But on my combo I find no advantage in the additional up to 8 degrees.
                The Jacob's unit, as I have now set it, allows up to 8 more degrees in every situation. It has a range of 15*. I haven't dicked with it in a few years now.
                But the thing to think about is that every combo is unique, and that there is a lot of potentials that some guys leave on the table by not exploring the timings of their combo

                On another note,using this same device is how I discovered the cure for my low-speed jumpiness. She likes retard at 500/600 rpm, pulling herself around the parking lot at idle in the 10.97 starter gear. Yup 14* was too much. Sometimes I take it down to the minimum 7 degrees......
                Rumpidy-rumpidy-rumpidy......ruumpidy.......ruumpidey...........rhuuumpideeey......
                 
              • KitCarlson

                KitCarlson Well-Known Member

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                I think your engine is crying for 3D electronic advance. :) That is one way to get it timed right all the time, regardless of driving conditions, or throttle position.
                 
              • TrailBeast

                TrailBeast AKA Mopars4us on Youtube

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                Well that's nice to know for sure guy's.
                Thanks
                 
              • mopowers

                mopowers Well-Known Member

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                Thanks for all the info guys. That is an ingenious way to limit amount of vacuum advance above.

                BTW, here's a chart with the BWD part numbers and specs for all of their vacuum advance canisters. It doesn't have the application info on it though. Maybe I'll go through and fill that it one of these days.

                vacuum advance chart.png
                 
              • TrailBeast

                TrailBeast AKA Mopars4us on Youtube

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                We use these for our advance modded distributors. FBO Systems
                 
              • mopowers

                mopowers Well-Known Member

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                Yeah I'll be picking up one of those for my dad's truck as well. Thanks.
                 
              • gliderider06

                gliderider06 Well-Known Member

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                Very Interesting! Can one also limit the amount of advance by cutting/welding about 1/8" out of a 11R arm? I need to limit my total Vacuum advance myself.
                 
              • AJ/FormS

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

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                No shortening the arm only repositions the advance plate.

                When you are checking over the chart, bear in mind that not all of those fit on the same engine; some are for point-types,some for electronic, and some are for counter-rotating dizzys.
                 
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