I have searched and read too many threads to count. The only thing I have concluded is NOT to use E3, Splitfire, etc. I have even seen that the NGK V-Power is not liked as much the standard NGK.
First, I have a 1997 4.0L Automatic. I am using the Davis Unified Ignition Firepower Kit, performance coil, cap, rotor and wires. DUI recommends the Autolite AP985 (single platinum) gapped to .065". It is nearly impossible to gap these that much, so I settled on .050".
I had an issue that ended up being fuel related. In the process of diagnosing, I took it to a friend at the dealership. He frowned on the use of Autolite in a Jeep. He also said the AP985's were a little too short. At first glance, they do look slightly shorter than the Champion 412's. Once the seating rings are on, they both seem to have the same amount of thread left. The Champion's ring is much thicker. Once seated, I'm not sure how much difference there would be.
I have read that the stock 1997, 4.0L likes plain old copper plugs. But my ignition isn't stock.
I have read that Champions from the dealer are better than the ones from the local autoparts store, even with the same part number. I find this a little hard to believe. Differences of batches mabye, but a "better" plug???
I have also read that some dealerships are switching all their plugs (even for older Jeeps) to NGK because of quality issues with Champion. Even though, my friend has heard no such thing.
Are there any EDUCATED opinions about these plugs? What about platinum vs. plain copper?
I am most likely going to try a set of NGK 6779's (non-V-Power) next. With my ignition I will be trying .050" gap again. Unless someone can give me a better choice...
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I would use copper. Copper is the best material for a spark plug in terms of performance. It will require a change more often but it is better. I know of big horsepower motors running on copper plugs because the performance is just better.
Just match to an NGK that is proper and will be the correct temp plug.