every 3000 miles - its better for the life of ur car anyway w/ the nos set up. I tried HKS iridium #7 and they werent ideal, and then i went back to the NGK platinums, but now i'm on ngk coppers since the big nos users recommend them so much.
a quote from 2 yrs ago:
"call me when you are man enough to go to a *real* track and run some *real* times or are you afraid you might mess up your cool snow plow front bumper or your darth vader hood??. Until then Jack "I don't know how to turn a knob" B. you have nothing to say about me or my car. Put up or shut the f*ck up :-)." Kyle "Grumpy Bear" Puckett