newbC6

I am swapping out TR6's for some NGK 7's. What would be a good gap for a LS2 running around 7 lbs and 100% meth at 4 psi? .30?

JetstreamGS

.030 should be fine. I’m wondering will switching to a colder plug affect the tune?

CI GS

Why are you switching to a colder plug? For that level of boost and meth, I would put a stock LS9 #41-104 Iridium plug (= 6 NGK heat range) in it and forget about having to gap it. I’ve run that plug on both pump 93 + BOOSTane and 104 race gas at 12+ psi of boost with no meth and never saw any sign of KR and it idled perfectly.

newbC6

Well ive developed a slight knock at and above4 psi of boost. I've had the same tune for the last two years and I noticed it this summer on 90 plus days . its tuned at 91 and ive been running 93 and tossed in some mmt to see if that would eliminate it. Im trying to avoid taking it back to the tuner at this point and wanted to see if a colder plug would eliminate it. I'm not experiencing any noticeable loss of power just a slight rattle . I was thinking either spark or maybe carbon deposits causing a hot spot. The meth is 100% and comes in at 5psi.

Could a hotter plug or fouled plug cause any thing like that? Or carbon build up? ( it has 80k miles on her)

CI GS

Okay, if you can hear knock, that’s something to be concerned about, but it’s probably not so much the plug being too hot (a TR6 is a fairly cool plug) as it is a tuning issue - either a lean tip in condition/PE not coming in early enough, too much advance at that point, etc. Can you bring the meth in earlier at say 3-4psi? That may help to cover any lean condition and/or knock from too much ignition lead.
in any event going to a colder conventional plug may only make the car idle a bit tougher and foul the plugs quicker. If you did need a 7 heat range, then a TR7IX Iridium plug would be a better option than a regular plug, in my view.

newbC6

I can switch it to spray at 3 (I believe) it's just a little boost switch. So bringing meth on earlier shpuldnt affect my AFR correct? No need for a re tune. I will give it a shot.

CI GS

It may affect your AFR, but it may be that’s whats needed (if it’s actually going lean for a bit). I’ve never used meth so I’m not sure how you control it, but if you can bring it in a little earlier, that should cover any lean spot you may have. Ultimately, I think you may need soon tuning to deal with this issue, because I really can’t see why you would need a #7 heat range plug.
BTW: Do you have a wideband on the car? If not, it would be best if you got one and a Dashlogic and you can monitor the AFR, timing and all sorts of things, which would take the guesswork out of trying to troubleshoot issues like this.