Like livvie said, many long threads on this. Bottom line is this: Octane is only needed to ensure the gas/air mixture does not ignite prematurely when compressed. Engines with high compression ratios need higher octane for this reason - to prevent combustion. Octane does not add any performance into the gas itself. Typically, higher performance engines have higher compression ratios, thus needing higher octane gas. Because all these high-end performance cars need high octane gas, people generally assume the gas itself is "high performance gas". It's not. Go with what the manufacturer recommends. Running 91 octane in a car that requres 87 does more harm than anything.

*** Retired after 65,000 outstanding miles ***