Timing Light Accuracy

Electrical and Ignition

  1. mopowers

    mopowers Well-Known Member

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    I've been running 91 oct E15 CA pump gas. Heads are RHS/Indy X prepped by IMM. I'm assuming by 'Q' you mean quench? I'd have to double check, but i believe it's around 0.037"? If I recall, pistons were 0.015" out of the hole and I'm using 521SD gaskets.

    I'm picking up another timing light tomorrow btw.
     
  2. yellow rose

    yellow rose Master Of Insanity

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    I've seen 4 different timing lights give 4 different readings. Buy a new, non dial back timing light and if your damper isn't degreed get a timing tape and ONLY use THAT timing light. Let the plugs tell you how much timing you need on THAT timing light. I don't care if it says 20 total or 60 total.

    Obviously that's an exaggeration, but I've seen up to 6 degrees difference in lights. Buy a light and use it on your stuff.
     
  3. RustyRatRod

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

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    Problem is, it's hard to find a decent one now because none of these new POS "cars" needs a timing light.

    ....and I ain't payin 300 bucks for somethin off a tool truck. YR makes a lotta sense. Just buy one and go by IT.

    btw, @yellow rose .....where you been pecker?
     
  4. yellow rose

    yellow rose Master Of Insanity

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    Busy busy busy. I have one more load of laundry to do tonight, and as soon as the dishwasher is done (I suspect about an hour and a half from now) I'll unload that pig and be done for the night. Tomorrow starts all over. My parents aren't doing well and I'm taking care of them for awhile. After two years of taking care of the inlaws I hoped I'd get a break but evidently, 2019 is going to be another year of taking care of family.
     
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    • RustyRatRod

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

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      You have my admiration for that. Will add them to our prayer list.
       
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      • AJ/FormS

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

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        Those are Iron heads, right? Glad you figured out how to make that work. I bet that's a sharp combo.
         
      • mopowers

        mopowers Well-Known Member

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        After using a buddy's Matco timing light this weekend, it gave the same reading as my old Craftsman. Apparently this little 340 just likes a TON of initial ignition timing - I ended up with 30* initial.

        Yes, they're iron heads.
         
      • yellow rose

        yellow rose Master Of Insanity

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        If you are using an aftermarket box of a Chrysler module the timing retards with RPM. You can't see it with a timing light, but it happens. As much as 2 degrees per 1000 RPM.

        I've never lost sleep over a timing number that seems high to everyone else. Most guys don't test. They only do what others have told them.

        If your stuff runs better with 30 degrees initial with your timing light, do it. Unless it's hurting parts.
         
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        • mopowers

          mopowers Well-Known Member

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          I've got a 4-pin GM HEI. Seems to run the same with a couple different ones.
           
        • Mike69cuda

          Mike69cuda 64 is the new 17 FABO Gold Member

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          Could be inaccurate timing marks. If the engine has been apart over the years, who knows. If you feel like chasing it some more the next move would probably be to check it with a piston stop & see if TDC is really where you think it is.
           
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          • mopowers

            mopowers Well-Known Member

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            That was the first thing I checked and the mark is dead nuts.
             
          • yellow rose

            yellow rose Master Of Insanity

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            That's OK because the HEI will retard with RPM too. You can't see it with a timing light but you damn sure see it with a good distributor machine. That's why locking out the timing is a bad deal.
             
          • mopowers

            mopowers Well-Known Member

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            Are there HEI modules that don't retard with RPM?

            Would it worthwhile to screw in as much timing it takes to make it detonate, then pull it back some? Seems like a light becomes pretty useless if the ignition is retarding on it's own at RPM.
             
          • yellow rose

            yellow rose Master Of Insanity

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            I'm not up on the HEI as I should be. But, most any electronic device has a slew rate so I'm pretty sure every HEI has retard with RPM like any other. How much you can only learn by testing the entire system with a distributor machine. And then tune accordingly.
             
          • KitCarlson

            KitCarlson Well-Known Member

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            Perhaps some quantitative information about timing lights and ignition delay would be helpful.
            Xenon strobe tube flash delays are typically a few microseconds. A microsecond is a millionth of a second. That delay is fairly small, has little impact setting base timming, and only fractions of a degree even at 6000 RPM. 6000 RPM divided by 60 converts RPM to 100 Hz, then multIply by 4, is 400. The reciprocal of 400 is 0.0025 or 2.5 milliseconds.

            The turn off time for an ignition transistor, modern IGBT is also a few to several microseconds. Old style bipolar or darlington transistors may be 10 times slower.

            At 6000 RPM, on a V8 ignition events occur at 90 degrees intervals of crank. The time between ignition events is 2 5 milliseconds. As an example, 5 microseconds delay divided by 2.5 milliseconds, times 90, is only 0.18 degree.

            Mopar variable reluctance distributors have more significant errors, a few degrees due to runout, slop, and crude powdered metal reluctor, and other mechanical parts and linkages.
             
          • Johnny Mac

            Johnny Mac www.blueprintengines.com FABO Vendor

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            I have that same one...works well for me, even with digital and cdi ignitions.
             
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