in the small block you used an ar52? or an ar53? sometimes it works for some,, who knows,, its been better than ngk for me,, id have used an ar53 gapped at .045, did you open the gap up from out of the package? did you try different plug gaps?


for an indy 572 head you would use an ar3910 with 15/1 ive never seen anything in idexing aslong as the ground strap doesnt hit the piston