[MarkoPolo]

I do use 91 octane (Premium in Colorado) when I am towing. I figure 10 cents a gallon more is not that much. No problems with spark plugs or anything else. I truly was skeptical of this engine when I first researched it. I listened to to many internet trolls, I guess. But I am completely satisfied with it. I can't believe how much power is available when needed. It does seem to give you sort of pseudo diesel performance without all the hassles.