It's two heat ranges colder than the stock plug. When should you EVER jump two heat ranges just for an intake and some exhaust? Most L36/L26 owners I've seen running the 104s or NGK equivalents end up fouling or suffering mileage. 605s are right on the money and that goes for some of the most modded N/A builds you can think of.

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2004 Impala LS - got some mods
NAIOA Moderator

Making you think twice before picking on Impalas