Not really... posted by Snoguitar on May 16, 2003 at 03:10 PM
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in simple terms the rate at which the gas evaporates. Translated into combustion terms its the rate of volitility or how fast and completely the gas burns when ignited. Thats why your nissan states "premium fuel only". You'll notice if you run lower octane fuel the engine detonates and on some cars they get the "run on" characteristic. This is caused by a slower rate of burn or a low volitility. When the engine is hot and you shut the car off the engine wants to continue running because there is still unburned fuel continuing to burn and produce combustion even without ignition. Each time the engine chugs and the piston cycles it pulls in more fuel and the burn cycle continues to ignite the incoming fuel and so forth. With an engine that produces positive intake pressure such as the TTZ detonation becomes more critical. As you force air into the cylinder you in effect increase the compression ratio, the more you force the higher the ratio, simple math. Since a turbo charged or supercharged, or any other way you can cram more air into the cylinder relies on the rate of rotation or RPM it becomes more critical that the fuel rate of burn (volitility) is as high as you can get it or at least at or above the known acceptable limit.
