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Discussion Starter #1
Okay, I have searched and searched on here and can not find the info I know I referenced 7 years ago, last time I replaced my plugs. I know after much research at that time I bought NGK 7781 plugs, and there was discussion about slightly different gapping than factory and I had followed this. But I can not remember what gapping info was discussed. Any of the other longtime members know what i am referring to or anyone have any info for me? Thanks!!!
 

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My recommendation is the recommended 0.050 plug gap. A wider gap may give a “hotter” (higher voltage) spark, but that is also higher stress on the coil insulation and can lead to early coil failure (they do fail). The gap of course also wears wider over the miles, so it’s important to replace them on a mileage schedule (I recommend 75k miles or earlier rather than the factory-recommended 100k miles - also reduces chance of plug binding up in the cylinder head threads - also use anti-seize sparingly on the spark plug threads - keep it away from the tip where it could vaporize onto the plug tip insulation, shorting out the plug).

It could very well be that many of the coil failures happen because plugs were either “over gapped” (on purpose or accidentally) or left in too long (worn electrodes => wide gaps), electrodes broken off (Bosch plugs) which gives huge gap and coil stress, or people messing around and temporarily firing the ignition with plug not installed or not grounded - also huge effective gap and coil stress, and plugs installed with low torque causing high resistance to ground also resulting in high voltage across the insulation and potential for arc-over.

The coil has the capability of putting out *way* more voltage than the insulation can handle. When the spark plug fires, it shorts the coil output to engine ground, limiting the actual peak voltage to that point in the rise of the coil output at which the gap fires. Wider gap => higher voltage on the coil’s insulation. The first time the voltage arcs thru the insulation weakens that point in the insulation forever, making the arc-over threshold at that point in the insulation lower from that point on - it effectively punches a hole thru the insulation, creating a new easiest path to ground. Any subsequent arcing thru that point makes the hole bigger and also creates a carbonized (conductive) track (path to ground) from the charred insulation material.

Go ahead and over-gap your plugs if you want to totally wreck your life (just kidding). Seriously - do it if you want. Just make an informed decision and be aware that you’re increasing the chances of coil failure over time if you do. Replace or re-gap earlier (maybe 50k miles) if you do because the gap grows further as the electrodes wear.

EDIT: I just looked it up in the FSM. Plug gap spec. is 0.048-0.053”. I target to 0.050, if I’m just under, I leave it. If a little over, I tweak it down until I’m at 0.050 or just below. Remember - the gap grows with miles.
 

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I buy the NGK 7781 for the 02+ cars and purchase the Champions for the 98 - 01 cars. I always get them from rockauto because they are so damn cheap!
 

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Discussion Starter #4
Okay, thanks...I think that is what I was remembering is people gapping them slightly more for a hotter spark. This old gal just turned 180,000 miles the other day and is celebrating her 17th bday as well as my 8 years of ownership this month. Still in great overall shape and need her goin for awhile longer!!!
 

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Excellent job of keeping her on the road!

Thanks!!!! Best car I have ever owned. This one will be painful to let go of when the time comes :(
 

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What does your "hotter spark" expanded gap get you according to your research. Curious.
 

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Discussion Starter #8
What does your "hotter spark" expanded gap get you according to your research. Curious.
Like I said, couldn't find the old threads to reference, just remember conversations about it. Personally I don't care much, I will be going with the .050, just figured I would ask if anyone remembered before proceeding. :)
 
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