Armen
Serious Thumper
Offline
Half-Witted Wrench-Jockey from Jersey
Posts: 1452
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Good question. First of all, let's start with what is the octane rating? All gasoline can burn fast. All gasoline can explode. In an engine, gasoline exploding is called 'Detonation'. When gas becomes hot enough, it will explode. A particular gasoline's resistance to exploding is rated in octane. By refining a gas further and throwing in some additives, the octane rating can be raised. The gas in the engine can become overheated from many sources. Very high compression-them more you compress the fuel/air mixture, the hotter it gets. SO, higher compression motors run the risk of detonation with lower octane fuel. Outside factors-ambient temperature or lack of cooling (sitting in traffic in the summer), can raise the motor temperature and cause detonation. Incorrect fuel/air mixture, incorrect timing, tight valve clearances, incorrect oil will also make the motor run hotter. A poorly designed combustion chamber will also promote detonation (way long explanation for that). So, if a bike is prone to detonation, higher octane fuel may solve or reduce the problem. Having said that, understand that the same fuel that is more resistant to exploding, is more resistant to igniting. So, if a bike is happy on 89 octane beaver piss, using OhMyGodItsSoHigh octane fuel, may make the bike harder to start, run worse, and leave more unburned crap in the combustion chamber. So, I run the lowest octane the bike is happy with. Oftentimes, brand name gas stations put additives in their fuel to make them work better (detergents, etc), so I usually buy brand name gas from a station that moves a lot of gas (selling more fuel means the stuff has less time to sit in the underground tank and get nasty).
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