It�s not unheard of for people to go one grade colder (to an 8) on XTs, but there�s really no need unless you�ve done some serious tuning which results in higher combustion temperatures such as raised compression etc.

As for iridium, some people swear they can feel a difference, but personally I can�t (other than cost). I think most people that notice a difference in performance (usually claims of smoother running) do so simply because they�re going from an old plug to a new one; they�d probably notice the same improvement just putting a fresh standard plug. The main reason iridium plugs exist is that they last longer so manufacturers (of cars particularly) can extend service intervals, not to improve performance.

If you do decide on iridium just watch out for fake NGKs, of which there are quite a few circulating on eBay. If the price looks too good to be true � it probably is!

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