I was always told that all gasoline has the same BTU energy potential. The additives that increase the octane to 89 or 92 prevent knocking that occurs with higher compression engines. That using 92 octane in a car rated for 87 was just a waste of money. 
- Jim
'96 Mystique GS, Ztech - ATX,
with CD changer, Sylvania Cool Blues, sunroof, keyless entry, and 9mm blue wires
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