Originally Posted by sonoronos
Where did you get your 2-5 hp number from? Or is that sort of a....back-of-the-buttcheeks sort of number?
Yes. This is a number that is as you put it so eloquent "back of the butt cheeks" I guess what I am trying to say and was unable to: "if you use regular in X-fires, unless you drive it very hard you will not experience pinging and it will not damage the engine, but you will loose a minute (1-20 HP) power.
IF OTH you drive it hard, then by all means use premium. (Or super for our EU friends). Another thought: If you run regular on a regular basis then changing the spark plugs to one step colder may be a smart idea. Just an additional thing to keep detonation from occurring.