Originally Posted by jmproductions

I posted this on another thread about a month ago:

I changed my plugs from the NGK TR-55 (copper) to the AC Delco 41-985. Truck idles and runs noticeably better. Here is what I have learned about spark plugs in our NA motors recently:

1. According to a dealer technician: OEM plugs have been made by NGK (.060 gap, this is the one that says AC and NGK on it), Denso (? gap) and AC Delco branded only (.040 gap). Which plugs your truck originally came with depends upon when it was made.

2. The current correct OEM plug is the AC Delco Iridium 41-985 for all V8s (4.8, 5.3 & 6.0) gapped at .040. I kind of doubt that this one is made by NGK because their iridium plug is supposed to be gapped at .060.

3. A copper plug (and many other brand platinums according to an expert) will not perform properly and should not be substituted for any of our OEM platinum and iridium plugs.

4. Plug construction is also a factor in determining proper gap.

5. Platinum and Iridium plugs should NEVER be regapped because there is only a small deposit of the rare metals on the electrode and it can be easily be damaged or rubbed off.

I learned this through painstaking research over the last few weeks, I hope it helps anyone interested. Obviously people running nitrous or FI have other issues to consider in determining which plug to use, for the rest of us I wouldn't consider using anything other than the AC Delco 41-985 or the NGK PZTR5A-15.