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Plug Wire Extenders Compared

Discussion in '308/328' started by DWPC, May 23, 2011.

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  1. DWPC

    DWPC Formula Junior

    Mar 10, 2011
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    Dennis
    #1 DWPC, May 23, 2011
    Last edited by a moderator: Sep 7, 2017
    My sub-3000 RPM roughness was due to arcing at my plug wire extenders. All eight were burned through, several really blown out. I believe these Mayer extenders were OEM if not original.

    The comparison between the Mayer and Kingsborne clearly shows the big spring clip in the Mayer parts that almost touched the insulator vs. the compact circular clip in the Kingsborne.

    Since pulling the distributor caps to check plug wire continuity (all OK) is an undertaking in itself, I replaced the wires with new Taylor 7mm from SFI anyway.

    The new extenders smoothed the motor up nicely under 3000 RPM, making it pleasant to drive even at boulevard speed.
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  2. climb

    climb F1 Rookie

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    #2 climb, May 23, 2011
    Thanks for the pics. I've heard of the arcing causing holes but have never seen what they look like until now. I'd checked mine a dozen times looking for evidence of arcing but didn't know what to look for.

    Have no idea if the spring has an influence.
     
  3. maestro8

    maestro8 Formula 3
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    #3 maestro8, May 23, 2011
    It absolutely does. Think of the pointy end of the spring as a miniature lightning rod. The electrons will tend to gather at that point, and when enough do, they'll "jump" to the engine from there. Hence the arcing and damage to the boot.

    The more symmetric, circular design will receive charge evenly. Without a point of concentration, the charge will have much less tendency to jump the gap to the engine. It's not to say that it can't or won't arc, but the circular design will make it harder for the electrons to do so...
     
  4. tempest411

    tempest411 Formula Junior

    Dec 3, 2010
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    #4 tempest411, May 24, 2011
    I would think for that to happen you'd have to have awfully high resistance across the spark plug, as in from a very lean A/F mixture.

    Has anyone tried using a set of wires from an engine that has the 'extender' built into the whole wire assembly, as is common practice today. DOHC Honda engines might be a good place to look. Getting rid of the extender would eliminate a point of possible failure.
     
  5. robertgarven

    robertgarven F1 Veteran
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    #5 robertgarven, May 24, 2011
    Wow , Ive been looking at mine for 16 years and never seen any thing like that are you running a non stock ignition?

    Rob
     
  6. Tony K

    Tony K Formula 3

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    #6 Tony K, May 24, 2011
    Excellent illustration, Dennis. When I replaced the extenders in my GTBi, I made a point to buy the ones where the clips were as narrow and close to the center as possible.
     
  7. mwr4440

    mwr4440 Five Time F1 World Champ
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    #7 mwr4440, May 24, 2011
    A few of my OLD extenders looked like the least effected in the photo above.

    Actually the burn "holes" looked like the residue normally associated with a location of where the plastic was injected into the mold.



    Look CAREFULLY with magnafication and you will likely see the burns better IF they are there.
     
  8. DWPC

    DWPC Formula Junior

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    #8 DWPC, May 24, 2011
    Last edited by a moderator: Sep 7, 2017
    The four holes in the extenders on the right are small and less dramatic than the craters in the others, but simply zooming the pics shows they are scorched, are irregular and at slightly different distances from the lip.

    (Picture of all eight extenders reposted...the pic in my original post is not showing)
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  9. DWPC

    DWPC Formula Junior

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    #9 DWPC, May 24, 2011
    The ignition is all standard. All I can assume is that the old extenders came from a bad batch. The internal clip design certainly aggravated the problem. Once the shell pitting began, the arc path to ground through the insulator became progressively more direct. I'll be checking the new extenders frequently to ensure the problem was the extenders themselves and not something else, though I don't know what else it could be.
     
  10. BigTex

    BigTex Seven Time F1 World Champ
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    #10 BigTex, May 24, 2011
    What spark plugs were you using??
     
  11. mwr4440

    mwr4440 Five Time F1 World Champ
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    #11 mwr4440, May 24, 2011

    I am with you.

    I am just explaining that someone here COULD be confused between your pics of real failure and a normal manufacturing asthetic "defect."
     
  12. DWPC

    DWPC Formula Junior

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    #12 DWPC, May 24, 2011
    Last edited: May 24, 2011
    They're NGK but to tell you the truth, I don't know which ones. I checked them when they were out for the compression test, but forgot to record the number. They looked good but only had about 500 miles on them.
     
  13. BigTex

    BigTex Seven Time F1 World Champ
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    #13 BigTex, May 24, 2011
    I ask because the extenders are "resistor and non resistor" IIRC....

    It looks like those early extenders for non resistor plugs might have been bucking some resistance in the plugs themselves.

    I have run the stock c clip extenders for years, (and find some off brands mixed in on one of my cars) so I doubt that could have been the actual cause of the failure....NGK BP5ES here.
     
  14. DWPC

    DWPC Formula Junior

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    #14 DWPC, May 24, 2011
    Both the old Mayer (Mafer?) and new Kingsborne extenders are non-resistor. Kingsborne lists different extenders (red) for 2V engines as 2K ohm.
     

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