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Both of the previous posts are very close to why octane is important.
The amount of octane depends completely on the speed of the flame front as it propagates across the cylinder after initial spark. If an engine is designed that has a flame speed that progresses too quickly, and the engine designer needs to slow it down, then a higher octane fuel is specified. Higher octane fuels burns more slowly than lower octane fuels.
Now, the Japanese motorcycle engines are specifically designed for lower octane fuels, and will generate the most horsepower using these fuels. *If* you spend the extra and put higher octane fuels in these motors and dyno test the engine, you will see a drop in horsepower due to the higher octane fuel. This is because the flame speed is now too slow!!
When an engine has just enough octane to prevent detonation, then no further increase in octane level is required. Going higher in octane will just cost you more in fuel and reduce the specific output of the engine. The right amount of octane = the right amount.
Jim.
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