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					Originally Posted by ganseg  Pure gas has about 20-30% more "power" than ethanol, but we are only talking about up to 10% ethanol in your gas.  Lets use 25% less power on that 10% of your fuel - that is a 2.5% difference.  93-91.5 octane is a difference of 1.6%.  Either way, you can't feel or measure that in power or gas mileage.  
 Where I am willing to spend a little extra money is when my car is sitting and when I go to the track.  And I would start filling with pure gas at least a fillup before my last fill so that when it goes in storage or to the track, the whole system is pure gas.
 
 I would not add octane.  The little tubes of it you get at gas stations and autoparts stores add like .1 octane.  There are bigger cans of a worthwhile product called Race Gas that can actually bring fuel up to 100 octane, but that is not for the average situation.
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Thanks for the math lesson as I forgot my HP:-)