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"But how do it know?"
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Hi All,

I have some questions regarding spark plugs that I haven't found complete answers to. If any of you can shed a light, it would be greatly appreciated.

  • What is the significance of the spark plug gap?
    For me personally, the question stems from the fact that, while working on getting my truck running right, members often asked if the plugs were gapped to 0.045". Interestingly, when I did the first tune up on the truck when I bought it, the plugs were gapped to about 0.055". However, I have kept the gap at 0.060" for the California HD specs and haven't noticed any issues yet.

  • What is the importance of heat range?
    Quite often I read about members recommending or mentioning the fact that they are running colder plugs. Under what circumstances would one do that?

Thanks in advance,
 

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lt1silverhawk said:
Hi All,

I have some questions regarding spark plugs that I haven't found complete answers to. If any of you can shed a light, it would be greatly appreciated.

  • What is the significance of the spark plug gap?
    For me personally, the question stems from the fact that, while working on getting my truck running right, members often asked if the plugs were gapped to 0.045". Interestingly, when I did the first tune up on the truck when I bought it, the plugs were gapped to about 0.055". However, I have kept the gap at 0.060" for the California HD specs and haven't noticed any issues yet.

  • What is the importance of heat range?
    Quite often I read about members recommending or mentioning the fact that they are running colder plugs. Under what circumstances would one do that?

Thanks in advance,
In large measure the gap depends upon the electrical power being supplied to the plug. A high power coil will jump a larger gap. A larger gap is one way of insuring the mixture catches fire and that the plug is less likely to foul across the electrodes.

Heat range is the selection of a plug that transfers heat from the electrodes and the in chamber portion of the insulator at a rate that neither fouls the plug with carbon from being to fast to remove heat (this is a cold plug) nor insufficiently removes heat such that it burns its combustion chamber side parts out (this would be a hot plug). The incorrect heat range can fake the observer into thinking the mixture and/or the timing is incorrect. A too cold plug will carbon up like too rich a mixture while a too hot plug will become fried white like the mixture is too lean. The higher risk is a too hot plug as it can glow hot which will cause preignition which is destructive to pistons especially and the parts connected to them. At the cold end of the scale a fouled plug will cause misfires, inconvenient but usually not instantly destructive like preignition can be.

Bogie
 
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