[raaaid]

well the bigger the better is not true check this wiki on octanes:

Octane" is colloquially used as a short form of "octane rating" (named for the ability of octane's branched-chain isomers, especially isooctane, to reduce engine knock), particularly in the expression "high octane". However, components of gasoline other than isomers of octane can also contribute to a high octane rating, while some isomers of octane can lower it, and n-octane itself has a negative octane rating

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for what i know the antiknokcing charachteristic dpened on what kind of engine

so the fuel is syn with engine, normally revolutions

i just learnt it can even be negative

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imagine i fuel creates a flame tongue in 0.1 seconds
the sync so the fuel doesnt expand while the piston contract and knoks depends on the speed of it

the antiknocking chararacthericstics of fuel that is the octanes determines how much does it take to burn