Originally Posted By: SirTanon
The last two sets of plugs I put in my car were supposed to be pre-gapped.
On one set, 2 of the 4 were undergapped (.044 instead of .051)
On the other set, all 4 were undergapped.. by even more.
I ALWAYS check.
Denso claims that the performance of their iridium plugs can make up for slight differences in factory-set gap. I'm a bit skeptical, but that's what they claim. Some people claim that standard plugs with nickel alloy electrodes actually run better, but of course won't last as long since the electrodes wear down. The precious metal electrodes of course fire through the thin wires, so I guess that prevents erosion of the nickel alloy around the thin wire.
I remember on my 1995 Integra GS-R the specified gap was a rather large 1.3 mm. I heard something about it running really hot as a result, and substituting standard plugs wasn't recommended.