I called NGK this morning after noticing the difference in gapping between the TR55 and TR6 (for reference, this is for both the V-Power and Irridiums, and the TR55 is one heatrange colder than stock, TR6 is two heatranges colder).
Factory gapping for us is .060". The TR55 comes that way and is fine. NGK'* website shows the TR6 gapped at .039", and I'd never noticed that before (I was re-gapping mine to .060", and this is what I called to ask them). The tech told me the TR6 is actually gapped at .032", regardless of the website stating .039".
At this point, I asked him what I should be gapping to, based on my mods. He gave me a range of .040" to .045" for the TR6 in my car, and he agreed that because of my hotter MSD coils (and the same would hold true for the 97+ SSEi coils) I should tend to the bigger side, or .045".
The general rule of thumb is never change the gap larger or smaller than factory gapping by .008". In this case, the listed gap of .039" could be safely raised to .047 for my TR6'*, but the ACTUAL gap as I was told of .032" could only be safely gapped up to .040". With that in mind, he told me I'd be fine up to .045", just pushing the PAPER limits. The idea is to keep the faces of center electrode and ground electrode as parallel to each other as possible, and if you go too far, you induce an angle on the ground electrode, so the gap isn't even across the face of the center electrode.
Now to dispel some incertainty with Copper, Irridium, and Platinum in Forced Induction applications:
Platinum IS CONFIRMED bad news in supercharged, turbo, or nitrous (and even alcohol/methanol) injected applications. Irridium is as good as copper, as the core of the Irridium plug is still copper, and it'* just an Irridium plating (it'* actually a copper plug pressed into an Irridium jacket).
The interesting part is that people playing with heatrange changes often select the wrong Irridium plug. In alot of cases, you should go another heatrange colder when switching from copper to Irridium. In my case, since I'm just barely into the 2 heatranges colder need, I'll stick with TR6 if I switch to Irridiums, but someone else more heavily modded would want to run up to the TR7.
NGK plugs are reverse of domestic plug manufacturers in their heatrange specs. The lower the number, the hotter the plug. Higher numbers are colder. So the TR7 is 3 heatranges colder than stock, the TR6 is two colder, and the TR55 is one colder.
I probably won't make the switch to Irridiums simply because of the frequency I change my plugs. I do it once a year. If I went to full lifetime of the plugs, I'd probably do it, but the difference between $2 a plug and nearly $8 per plug seems ridiculous for my frequent plug changes.
Here'* a good plug FAQ I suggest for anyone wondering about plugs:
This is an authorized distributor of NGK, but not NGK themselves. I got alot more information on the specifics of my application from NGK directly.
I'm buying my plugs from http://www.ngk.com/
(authorized DISTRIBUTOR, not NGK the manufacturer). I typically have to order my plugs from NAPA, as most stores don't stock the TR6 on the shelf. NAPA ships quickly, but this time I'm getting shipping to my door, rather than having to go to the store to pick them up.
I also briefly discussed O2 sensors with the Tech (who was VERY knowledgeable), and he'* checking on whether or not NGK makes the AC Delco O2 sensors. If they do, try this for comparison:
lists my O2 at $16.85 (p/n 21002)
lists my O2 at $26.40 (GM# 25162693 or AC Delco #AFS-20)
I'll be talking with him next week to confirm that the NGK is the AC Delco sensor in sheeps clothing
I'm in the process of getting my plugs and wires here for a swap before WCBF. Might have to do it DURING WCBF if they don't get here soon. I have a high resistance on 2 of my plug wires right now, and my plugs may be fouled by my recent troubles with my alternator. Last time my alternator failed, my spark voltages were low enough to foul out a set of plugs rather quickly.
Let'* use this thread to accumulate what we can for a Techinfo article.