If they are too cold a spark plug it would hurt your car not help it. What are your mods? Stock GTP's need Autolite 606's or 605's. Basic 3.4" setup's and maybe 3.25" rockered cars run Autoilte 104's. Anything lower IMO should run copper core 103's. I have a 3.25" Xp'ed setup (mods in sig) and I have run 103's since I put the cam in.