So, Quick Trip advertises that all their grades of gasoline are TOP TIER gauranteed gasoline(another TOP TIER gasoline is Chevron... if you don't know what it is just Google it). I have been using their premium 91 octane just like the owners manual says to but I've noticed that many of thier stations around Des Moines, IA have their Mid-Grade gas specd at 90 octane with a 10% ethanol mixture. Has anybody ran this gas or a similar gas with an 90 octane rating? Just curious if this might be ok. It would save alot of money in gas but if there is a chance it could cause knock/timing to be retarded/damage engine I won't even try it. Anybody?