Premium Gasoline

I recently bought a new Nissan Cube Krom, should I use regular or premium gasoline?

The owner's manual says "Use gasoline with a AKI higher than 87, research using 91 AKI gasoline"
But will using premium gas harm the engine?

91 octane is tough to find around here. A few nut not all Sunoco stations has it. If 91 octane is what the book says to use do not go down to anything less. It's perfectly OK to use a higher octane if you so chose. The higher the octane the slower and cooler it burns. As a side note, higher octane fuel prevents the engine knock sensor from retarding the spark advance. You'll get better fuel economy and horsepower.

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