Ignition timing for stock cam/heads Magnum 5.9?

Magnum Engine Swaps

  1. MRGTX

    MRGTX Well-Known Member

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    Have you guys experimented with ignition timing much?
    While I have gone through nearly every nut and bolt on my Dart in terms of body, suspension and drivetrain, I have never messed with anything on my Magnum 300 crate motor beyond bolting up the headers and changing the oil.

    It runs fine, doesn't seem to ping on 87...but something tells me that the ignition timing, which I've never touched is leaving something on the table.

    I have a fresh distributor ready to go in this weekend...then I'll get to know my timing light and figure out if I can get any more of those (supposed) 300 horses to come out of the barn once in a while.

    What has worked well for you? How much timing do these motors like? I am running a mismatched gear ratio (the 4.10 was not a great choice to match with the A904 as it turns out) so some higher rpm power would be helpful.
     
  2. AJ/FormS

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

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    What's wrong with 4.10s/ nothing mismatched about that for the street.

    That 300 is a sweetheart of a street engine, with a nearly flat powercurve from 4000 to ~5200, a long, long powerband, and good torque from 3000 on.
    I see the cam is advertised at 250/264/110 and if in at 108 then the Ica becomes 53*. If that engine is a 9.0 Scr then the pressure at 500ft elevation become 155psi with a 144VP which is fantastic and should be fine with 87 gas. That, with 4.10s should be a ton of fun. Timing wouldn't be a big deal in a streeter. Even if the power timing was 4* short of optimum, you'll hardly know it cuz she is accelerating so hard in the first two gears and hitting 65 at about 5300, and about time to shift.
    In the lower gears timing could be really slow before you notice it because the tires will be spinning ,seems like forever.
    But where you will notice lazy timing is in cruising at steady state; the fuel economy will be poor.
    3000rpm will be about 55mph with tall tires, and the timing there should be in the neighborhood of 55*. Or more. You can get 20 to 24 out of the Vcan, leaving 30/35 for the D to bring in.
    With that set-up to continue to burn 87, I would target 10 to 14 idle-timing, and 34* at 3400 Power-timing. The rest is a crapshoot, you can play with it for weeks and unless you do before and after time trials gains will be hard to find on the street.

    But if that is a 9.5Scr engine (I couldn't nail down the Scr from my sources), then you might be in trouble.
     
    Last edited: Jul 12, 2019
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    • TrailBeast

      TrailBeast AKA Mopars4us on Youtube

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      At 5,500 feet elevation and 9.1:1 compression ratio I run 18 degrees initial and 34 total all in by 2,500 RPMs.
      Vac can makes my grand total cruise timing right at 52 degrees.
      I normally run 87 fuel.
      This is a 5.9 stock short block, Engine Quest CH318B heads with 1.92 intake valves, 214/224 cam, 1.6 rockers giving .512 lift.

      Unless you live up in the mountains you should probably stay around 16 initial or you could end up with some detonation on 87.
      Also pay attention to your total timing. (initial plus mechanical without vacuum advance)

      With an overdrive you could get pretty good mpg with that motor.:D
       
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      • AJ/FormS

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

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        Awesome even with a smaller rear gear, better than any factory 318 ever.
         
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        • MRGTX

          MRGTX Well-Known Member

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          So I just to be on the safe side, I started with 10* initial and I’m noticing some sluggishness when rolling into the throttle at low RPM. When cruising at low speeds I may be hearing some pinging but I’m not completely sure.

          Am I not running enough advance? I’m hesitant to go more advanced if that is in fact a ping.
           
        • rumblefish360

          rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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          I had it just like trailbeast pretty much. 15* initial, 34* 25/2600 rpm, 52 @ cruise. This works great for the street.

          A strip tune is more aggressive and not really warranted for the street. It just helps burn up tires! You should not have a problem doing that now.

          Re tune the carb a bit and let ok for the maximum vacuum reading possible. That will get it running crisp!

          .
           
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          • MRGTX

            MRGTX Well-Known Member

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            So I'm right at ~15* initial timing and it's significantly better! Still not impressive but better.

            I did discover that the vacuum line (connected to the side/lower part of the carb) is totally inactive. So I guess I'm running on only mechanical advance.

            Could this explain why my car feels slower than it should or is the vacuum advance really only helpful in establishing initial timing?
             
          • rumblefish360

            rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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            The way Chrysler set up the distributor and the vacuum advance is different from others. The vacuum line runs to a ported entry. This means that the vacuum line operates once the throttle is cracked. Not at idle. There could be some vacuum on that line. This is why they tell you to disconnect the line and cap it to set initial timing and then reconnect it on the final step to test for 52*’s max timing.
             
            Last edited: Jul 30, 2019
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