29 Oct 11 10:44, Mark Hofmann wrote to Roy Witt:   
      
      
      
    RW>> If your Dodge had the Hemi V8 engine, it would have a dual coil over   
    RW>> with dual wires, one to a plug in the cylinder under it, the other   
    RW>> to a plug in the opposite bank. Yes, they have two plugs per   
    RW>> cylinder. One coil fires when the cylinder is near tdc, while an   
    RW>> opposite coil will fire the 2nd plug when that cylinder is on an   
    RW>> exhaust stroke. All in the name of emissions control. Someone told   
    RW>> me a hundred years ago that the Chrysler hemispherical combustion   
    RW>> chamber was inefficient and I guess this proves it.   
      
    MH> Our Durango has a 4.7 V8, non-Hemi.   
      
   I've worked on one of those. Reminded me of what they called their   
   poly-combustion chambered engines of the mid 50s.   
      
    MH> I didn't know that the Hemi engines had two spark plugs per cylinder.   
    MH> I do know that when you eventually change the plugs, they typically   
    MH> replace the coils at the same time.  Can be a bit on the expensive   
    MH> side..   
      
   Figure $112 for a double set of platinum plugs and about $50 per coil.   
   Ford uses a coil-on-plug setup that also requires replacement at plug   
   change time. At least they don't have to worry about replacing plug wires.   
   Sometimes those Ford coils die long before the plug is worn out.   
      
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