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Engine with high compression ratio requires high octane gas. I'm not sure if 300e's engine has high compression ratio.

BTW, Higher octane gas is not better than lower octane gas. It's just higher octane gas explodes in higher compression. My friend use 91 octane gas in his 91 Honda Civic which is completely waste of money. He insists his car runs better with 91 gas. Actually, what he need is a tune up and adjust the timing, etc.