Distributor curve help needed

Electrical and Ignition

  1. Ricks70Duster340

    Ricks70Duster340 Child of the King, widower FABO Gold Member

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    I just checked the curve of my stock distributor (ported vacuum blocked) and need some help to optimize. Car is a 70 Duster with a stock 360, stock converter, 3.23 gears, 28" tires. Distributor currently has FBO black & gold springs with no limiter plate.

    500-24*
    1000-24*
    1500-25*
    2000-27*
    2500-33*
    3000-38*
    3500-41*
     
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    • QuickDart360

      QuickDart360 Well-Known Member

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      Have you spoke to Don at FBO? He can help with the curve set up as well.
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      Yeah, it needs a limiter. 41 is too much total. That's a pretty low RPM for it too. It would probably work better with 34-36 total in by 2500-3000. How does it start hot? Does it lug the starter any? What about spark knock (ping)? 24 is gettin pretty high for initial.....but some like it. Maybe back it off to 20 and put the limiter on the 14* slots and see how it does. It'll probably be really close spring wise with one light and one medium spring.
       
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      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        Not sure I agree.................if it is starting out at 500 with no advance or not? timing at 24BTC at 500? If so there's less than 20 crank degrees in the dist????

        What kind of cam you running 24BTC initial and with a stock converter and 3.23??
         
      • toolmanmike

        toolmanmike Moderator Staff Member FABO Gold Member

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        Yep, way too much initial. 15° is probably enough.
        Set your initial at 16° and your total will then be at 33° which is about right.
         
        Last edited: Jul 16, 2021
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        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          a. Mostly for drag race or general use?
          b. Are you going to use vacuum advance?
           
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          • Ricks70Duster340

            Ricks70Duster340 Child of the King, widower FABO Gold Member

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            Not sure about the cam, but it feels dead stock.
             
          • Ricks70Duster340

            Ricks70Duster340 Child of the King, widower FABO Gold Member

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            All street use, and using ported vacuum
             
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            • Ricks70Duster340

              Ricks70Duster340 Child of the King, widower FABO Gold Member

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              No hot start issues. Pings just a little under load in 3rd gear (auto) when it is really hot outside.
               
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              • toolmanmike

                toolmanmike Moderator Staff Member FABO Gold Member

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                Zactly! A stock 360 doesn't need that much initial and non sure not that much total
                Yep back it up like I suggested. 24° initial is unnecessary and 41° total can get you into trouble with detonation. Let the vacuum advance ad in what it needs. You can usually adjust that as well through the vacuum port.
                 
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                • RustyRatRod

                  RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                  Yeah, it definitely needs the total limited. You may need to back off initial.....but I wouldn't do it if it doesn't rattle once you get the total limited to about 34 or so.
                   
                • 67Dart273

                  67Dart273 FABO Gold Member FABO Gold Member

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                  Pretty much what I was thinking.............if I understood his post, 41 and 24 is 17* crank in the distributor which should be fine I'd think
                   
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                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

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                    OK. So my suggestion is to reshape the curve.
                    But you can start with simply reducing the initial.
                    I would not take it down to 15* just yet. If you do, it will probably be a dog from off idle to3000 rpmish when you stomp on it.

                    Here's what you measured.
                    upload_2021-7-16_12-26-48.png

                    Try something like 18* at 500 rpm.
                    upload_2021-7-16_12-33-46.png
                     
                  • Ricks70Duster340

                    Ricks70Duster340 Child of the King, widower FABO Gold Member

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                    I did put it back to 16* initial and it is most certainly a bow-wow. Very lazy at low speeds. Will put it up to 18 and try again.
                     
                  • RustyRatRod

                    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    Yup I figured. LOL The reason is because it has LOW cylinder pressure. That's why it likes a LOT of timing and if you back it off, it'll run like a dead dog. It's just something you're gonna have to play around with.
                     
                  • CFD244

                    CFD244 FABO Gold Member FABO Gold Member

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                    Make sure that your balancer is true TDC. Maybe you are not at 24* at idle?
                     
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                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      Made a goof in the graphs above (at 3500 rpm) when I plotted out the timing you measured.
                      Fortunately doesn't change the main point.

                      In gray is the range where I think the timing ought to be.
                      upload_2021-7-16_12-50-56.png

                      So the next question is how to get there.
                      The first thing to do is reduce the tension of the primary spring. That's the spring with tension when the distributor isn't turning, or turning slow. On a Chrysler distributor you do that by turning the spring perch (circled).
                      upload_2019-1-26_18-55-22-png-png.png
                      You don't have to disassemble the distributor unless its really stubborn.
                      You can file a screwdriver into a tool to adjust from the top.
                      upload_2021-7-16_13-12-50.png
                      upload_2019-3-23_11-35-50-png.png

                      Or,
                      if both springs have tension on them, then turn both spring perches until they have the least amount of tension.

                      Or, better yet, if both springs have tension replace one spring with a long looped spring. In that case, don't reduce the tension on the primary spring. Not yet. Test first.
                      Example of a long looped spring.
                      upload_2019-5-23_10-38-4-png-png.png
                      The loop length and perch position determine how many degrees into the advance the second spring begines to assist.
                      But that's for later.
                       
                      Last edited: Jul 16, 2021
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                      • Ricks70Duster340

                        Ricks70Duster340 Child of the King, widower FABO Gold Member

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                        The pins in my distributor do not have those notches, so guess I will need to change the springs. Attached is a picture of my setup.

                        20210716_122114.jpg
                         
                      • Mattax

                        Mattax Just the facts, ma'am FABO Gold Member

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                        You might be able to drop it to 16 or less at idle. My concern was how it was going to respond when you drove it.

                        If its an automatic, you can experiment by checking for most power (least drop in rpm and vacuum) with placed in drive at idle.
                        But within 50 to 100 rpms above idle rpm, the timing should advance.

                        Take a look at the factory timing specs to get an idea of how quickly timing is added above idle rpm.
                        upload_2021-7-16_13-25-20.png

                        That was true even with non-performance cams (with less overlap and better compression at low rpm)
                        upload_2021-7-16_13-27-49.png
                         
                        Last edited: Jul 16, 2021
                      • Mattax

                        Mattax Just the facts, ma'am FABO Gold Member

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                        So with those you gently bend the perch.
                        Interesting though. I've only seen that on the Chrysler built magnetic pickup race distributors.
                        Wait. Is that a points distributor?

                        For street use. I'd still encourage using a long looped secondary spring.
                        With an ECU, for racing it will help insure no retard at top end.

                        8.5 on the governer (aka cam plate, aka slots) means there is around 17 degrees in the advance.
                        That matches well with what you measured. thumbs_up-gif.gif
                        Dont think you'll need to reduce the advance any.
                        I think you're pretty well set up if you pop in a heavy long looped spring and the softer of the primary springs. Then you'll be close enough to fine tune to whatever degree you're interested in persuing it.
                         
                      • Ricks70Duster340

                        Ricks70Duster340 Child of the King, widower FABO Gold Member

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                        I believe this was a points distributor that someone put a Pertronix unit into. I don't have a long looped spring, so should I replace the heavier black spring with a lighter one?
                         
                      • Mattax

                        Mattax Just the facts, ma'am FABO Gold Member

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                        You could try that.
                        Or if your good with shaping little things, make the black spring's loop a little longer.
                        Just a heads up that being a spring, not going to be able to bend it too many times.
                        I'm sure we can find you a long looped spring if you want.
                         
                      • Ricks70Duster340

                        Ricks70Duster340 Child of the King, widower FABO Gold Member

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                        I found a heavy long looped spring in my stash, so replaced the black spring with that. Also replaced the gold spring with the lightest which is silver. That change produced:

                        500-18*
                        1000-18*
                        1500-20*
                        2000-25*
                        2500-25*
                        3000-27*
                        3500-27*
                         
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                        • toolmanmike

                          toolmanmike Moderator Staff Member FABO Gold Member

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                          I think still too much initial and the heavy long slot spring doesn't get you to 34° at rpm where you need to be.
                           
                        • Mattax

                          Mattax Just the facts, ma'am FABO Gold Member

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                          ?u=https%3A%2F%2Ftse1.mm.bing.net%2Fth%3Fid%3DOIP.jpg

                          He's getting there.

                          He learn more going step by step and seeing the changes he makes.
                          beer-gif.gif
                           
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