The difference in 87, 89, 93 etc is not quality. It has to do with ignition characteristics. The wrong octane for a given engine, due to compression ratio, can either ignite prematurely or not completely thus causing very poor performance. And can also foul up sensors and such down the exhaust stream.
You can buy high quality 87 gas and also very poor 93 octane. Point being... Higher number doesn't necessarily mean higher quality.
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