What are my spark plugs telling me?

Engine, Transmission & Driveline

  1. WissaMan

    WissaMan Active Member FCBO Gold Member

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    Both are from 68 440's. To me they both look like the engine is running on the rich side. What do you think?

    From a 440 TNT, low miles on engine
    upload_2020-9-9_9-21-40.png


    From a "regular" 440, 101k on the engine. This engine burns some oil too
    upload_2020-9-9_9-22-43.png
     
  2. Pete Kaczmarski

    Pete Kaczmarski Senior Member

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  3. WissaMan

    WissaMan Active Member FCBO Gold Member

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    that's actually one of the sites I looked at. Mine don't look quite as bad as the one here (at the top) but they definitely look more like this one than the "normal" one below.

    upload_2020-9-9_9-47-6.png

    I'm used to seeing plugs like this one in fuel injected engines, but I wasn't sure if I could expect this kind of perfection on a carburated engine.
    upload_2020-9-9_9-47-51.png
     
    Last edited: Sep 9, 2020
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  4. Pete Kaczmarski

    Pete Kaczmarski Senior Member

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    One thing you did not mention, over how many miles or years were the plugs in the cars.
     
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  5. WissaMan

    WissaMan Active Member FCBO Gold Member

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    Sorry, the high-mileage "regular" 440 has all new everything in the ignition, between 500-1000 miles on it.

    The 440 TNT is unknown but I am assuming low miles . The person who sold it said he barely drove it after doing engine upgrades. Everything looks very new -- plug wires, distributor, etc.
     
  6. 413

    413 Well-Known Member

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    And what was the latest driving/running this engine did. What was the outside temps?
    My experience is that driving down the hi-way they look good. But if it has been a few cold starts backing in and out of the garage they look more like yours but will clean up with driving.


    Your plugs don’t look terrible. Cover the black threads with a paper and just look at the inside color and they look better. A cold engine is a little rich, or it will die. Warm it up by going down the hi-way for 20 miles then pull over and take one out and look at it.
     
    Last edited: Sep 9, 2020
  7. WissaMan

    WissaMan Active Member FCBO Gold Member

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    Last drive before the plugs were removed:

    The 440 TNT was driven about 25 minutes on a back road with 2 or 3 WOT blasts thrown in.

    The 440 regular was driven about 20 minutes into town and back with only mild throttle input.
     
  8. rkrochen

    rkrochen Well-Known Member

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    They don’t look terribly bad. As mentioned it all depends on the type of driving you are doing. You could try installing a slightly hotter running plug to see what happens.
     
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  9. RagTop66

    RagTop66 Member

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    Ok, so what’s wrong with my engine??? Just kidding, this is what happens when a timing belt on an Audi lets go, lol!

    FF256A51-95A5-4CFD-BA27-5CC5A602DF53.jpeg
     
  10. BigblueC

    BigblueC Senior Member

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    I've got one for you. Others that I worked with couldn't figure out why the equipment wouldn't run. Come to find out one of the employees had been shutting the engine down by engaging the choke at full operation. :rofl:

    upload_2020-9-9_16-37-1.png
     
  11. CBODY67

    CBODY67 Old Man with a Hat

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    To me, I don't see anything really out of whack, other than the brown coloration on the insulator. No fluffy black stuff to suggest a too-rich mixture and no oily places on the bottom of the plug threads or insulator. Gaps look decent, as does the general condition of the electrodes.

    Are they the correct heat range, or something close? Being on the "cold" side might be the reason for the brown coloration from things not getting hot enough, long enough, to burn the deposits/coating off?

    As long as they are firing reliably, just drive the cars and enjoy them. Before putting them back in, clean the electrodes' firing surfaces and gap just a tad wider then .035", like .038".

    Years ago, a drag racing article on reading plugs stated that the only way to "read" a plug was to make a full run down the strip, then cut off the engine and coast to a stop on the return road. THEN pull each plug out and look at them. Otherwise, the author claimed, you would not get a true plug reading. FWIW

    Just some thoughts,
    CBODY67
     
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  12. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Your plugs are telling you to put them back in the car and go have some fun and stop worrying.
     
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  13. fury fan

    fury fan Senior Member

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    I'm With Pete Kaczmarski, I also run Autolite. I have tried other brands over the years at various times, and lacking empirical data, simply feel that the Autolite gave me the best longevity.

    I run #86 (which is 1 step hotter than stock) in all my bigblocks, as all have been 90-150k engines. IMO, using 86s in place of what you are showing will look better, longer. I also run MSD boxes on everything, with hotter coils/wider plug gaps, and that all helps also. I now tend to go thru dizzy caps and rotors more frequently, but those are easier to change than plugs!
     
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  14. Knebel

    Knebel Senior Member

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    I'd go one step hotter.
     
  15. furious70

    furious70 Well-Known Member

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    The drag strip read is if you need to see your mix at wot. The principle is you want to only run them in the use case you want to check your mix for. Part throttle cruise is just as valid. Just don't do a bunch of varied driving.
    My normal plugs are usually lighter tan.
     
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  16. Knebel

    Knebel Senior Member

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    Last edited: Sep 26, 2020
  17. WissaMan

    WissaMan Active Member FCBO Gold Member

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    Thanks everyone. I'm going to start by going with a slightly leaner jetting and then check it again after a couple dozen miles.