Fiddling with idle timing and the 123 distributor

Discussion in 'E9 Projects and Restorations' started by Stevehose, Mar 4, 2018.

  1. Stevehose

    Stevehose Well-Known Member Site Donor $

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    So I've read some articles about advancing idle timing to the point where the vacuum and/or idle speed is highest then "backing it off" a degree or so to prevent pinging. This is the old school hot rod technique which while sipping my Manhattan last night I thought might have some merit. I suppose the theory is that idle increases because the higher timing makes the engine fire more precisely and efficiently, hence idle speed goes up without any additional fuel. Then they always say you have to watch out because your all-in timing will be way too high unless you get your distributor recurved. Well that's not a problem with the 123 because it can be recurved in 1 minute. Then I made another Manhattan and surfed eBay while contemplating this further.

    Today I hooked up the laptop to the 123 and manually advanced my timing from the 10 BTDC where it was currently set. Advancing it from 10 to 20 increased the rpm from 950 to 1200. If I went higher it started diminishing returns so I kept it at 20. No pinging at idle or off it.

    So then I recurved to go from 20 idle to 36 all in at the same limit as before. My total "mechanical advance" went from 26 before to 16 now with the elimination of the 10 degrees at idle. I then backed the throttle screw out and adjusted mix screws for AFR on the triple webers to get back to 950 at idle. Triple webers are sensitive to throttle plate/first progression hole position so this technique can also be used to dial that in. They also say triples "like more advance early on" so this certainly accomplishes that.

    Result? Eliminated a slight off-idle hesitation from before and it accelerates way better with no pinging. Transition AFR is a half point leaner than before (I was a little rich there but I've let it go as a triple weber quirk, now it's better) and runs great. Perhaps it's because I've eliminated an area of advance that the engine ineficiently ran through while accelerating off idle?

    Anyone ever try this or have any caveats for idle advance at 20? Want to try it yourself and report back? The improved idle with less throttle screw tells me that it is more efficient now. I am getting higher AFR's on overrun because the less-open throttles are dumping less fuel in than before. Here is the new curve:

    [​IMG]
     
    Last edited: Apr 15, 2018
    bfeng, zinz, Nicad and 3 others like this.
  2. autokunst

    autokunst Active Member Site Donor $

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    Hi Steve,
    Great post. I am looking forward to playing with these timing / advance curve settings when I get my 123 and triples reset this year. But I'm also a huge Manhattan guy, so this post spoke even more to me. :D Thanks for sharing this info!
     
  3. Ohmess

    Ohmess I wanna DRIVE! Site Donor $

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    Hi Steve -- I was looking at this last year, playing around in the 12 to 15 range. I believe I was at 12 at the Vintage, when you commented on the off idle issue. I need to get back to this soon.

    One other comment for folks looking at Steve's curve: note that you do not want the idle advance when starting the car as it makes starting much more difficult, which is why Steve's the idle advance does not kick in until 500 rpm (i.e. when the engine is running).
     
  4. sfdon

    sfdon Well-Known Member Site Donor

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    One point to ponder- many people set a higher timing number at the lowest idle row to keep the engine from dying when suddenly letting off the throttle.
    Then the preferred idle advance.
    The other issue I see is that load determines timing also. On MS ignition tables the timing is rpm and load dependent.

    Stolen with Citation from Hotrod.com......

    At WOT, the air and fuel are tightly packed and burn quickly, so we don’t need as much timing. At 2,800 rpm at WOT, 32 to 34 degrees of timing could be just about perfect for a typical pump-gas street engine. However, at very light throttle (14 to 16 inches of manifold vacuum), the air and fuel are far less densely packed in the cylinder. To make the most power possible at part throttle, we need to start the combustion process much sooner—perhaps as much as 40 to 44 degrees BTDC, depending on the engine’s individual demands.

    This much timing is only needed when the engine is under very light load....

    And lastly- mild street cams with long durations usually like 15 to 18 degrees at idle.
     
  5. Stevehose

    Stevehose Well-Known Member Site Donor $

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    Yes I think my Schrick cam likes this higher idle timing. And the additional advance from a vacuum source when load is low is why it theoretically helps cruise gas mileage. I might at some point play with adding back cruise vaccum advance, right now I am not using any.

     
  6. sfdon

    sfdon Well-Known Member Site Donor

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    I don’t miss that mechanical/vacuum/boost advance/retard circus!
    Nowadays we use advance/retard circuits to stabilize the idle.
     
  7. Stevehose

    Stevehose Well-Known Member Site Donor $

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    Me too, here's my recipe :)

    2 parts rye whiskey
    1 part Antica vermouth (the best imho)
    3-4 dashes Angustura bitters
    3-4 dashed Angustura orange bitters
    2-3 Luxardo cherries with a tsp juice mixed in
    Orange peel
    1 big ass cube of ice (from a specialty ice tray)
    Rocks glass

     
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  8. autokunst

    autokunst Active Member Site Donor $

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    Yum. That is almost exactly my recipe as well. Same vermouth - there is no substitute. The only difference is I favor Maker's Mark bourbon in lieu of the rye whiskey - just something I've come to enjoy.

    Okay, think I'm going to go make a cocktail. :)
     
  9. sfdon

    sfdon Well-Known Member Site Donor

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    Jeeeebus....
    The ice goes in the shaker!!!
     
  10. Stevehose

    Stevehose Well-Known Member Site Donor $

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    That's if you want it straight up like a martini. I like it on the rock!
     
  11. m5bb

    m5bb Well-Known Member Site Donor $

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    Now that everyone has had too much to drink I will ad that I do a similar thing with mine Steve. M30 motors like a lot of advance.
    Now that my compression ratio is under control ;) I should have a little less problem with some pinging at 3000 RPM.
     
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  12. jamesw

    jamesw Member

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    Great work Steve. Way to get the most out of the 123.
     
  13. Ohmess

    Ohmess I wanna DRIVE! Site Donor $

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    Dude -- you neglected to recommend a rye. I like Pikesville, with Bulleit as a backup plan.
     
  14. Stevehose

    Stevehose Well-Known Member Site Donor $

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    Yes Bulleit is my go to, when you're mixing it with vermouth and bitters there's no need to go too high end imho. I recently discovered Luxardo's liqueur which i will also add a little bit of.

     
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  15. brettsul

    brettsul New Member

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    HI Steve, are you able to repost the curve ?- it comes up with a cross through it.
    Many thanks.
     
  16. Stevehose

    Stevehose Well-Known Member Site Donor $

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    Fixed?

     
  17. sfdon

    sfdon Well-Known Member Site Donor

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    On a lower compression, smog exempt engine a lot of advance is wonderful.
    Lower engine temps at idle, higher torque, more stabile idle.

    On high compression engines with lower cranking speeds it can cause kick back.
    Too much advance can get you high Nox and HC along with popping. You can also get bad O2 readings because of the HC.

    On MS systems we have the ability to set advance timing at every rpm dependent on load. You might see 14* at 1000 rpm at idle but 12* at WOT at 1000 rpm.
     

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  18. brettsul

    brettsul New Member

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    Yes thanks Steve, I'll try that curve. Do you have the Vacuum map as well?
     
  19. Stevehose

    Stevehose Well-Known Member Site Donor $

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    With the triples I am currently not using the vacuum advance. I have some old ones I can post if interested
     
  20. brettsul

    brettsul New Member

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    Thanks that would be great.
     

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