This has all been hashed over before over in the fuels forum last summer. That was the situation that some fuels engineer finally came on there and said.


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Tommy Meisel says:

I gotta chime in as a mechanical engineer (retired) who has a basic understanding of engines and combustion processes. The size of the combustion chamber in these small two cycle engines and the frequency of combustion (at 7000 rom you light the fire 117 times a second) does not allow secondary flame fronts to form and collide with the primary flame front and cause ping. On your four stroke automobile, at 4000 rpm you are lighting the fire 33 times a second. A secondary flame front caused by preignition (aggravated with higher compression) has enough time to make it ping. Higher octane fuel just burns slower, that all. By the time any secondary flame front meets the primary one, it is too late.

Engines are designed to utililize certain fuel characteristics. On an engine that would be ping limited, if the manufacturer knows you are using a high octane fuel, he can raise the compression ratio, increase the timing and change the valve timing and overlap to increase power. Some do.

But our model engines are not ping limited.

Our gassers are pretty oblivious to the octane of the fuel. If it runs without preignition, the octane is high enough.

The manufacturer may specify higher octane fuel for other reasons, maybe he feels it has less additives, maybe he feels it gives him a competitive advantage by making his engines appear more sophisticated and needing "better" fuel. Who knows?

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Enjoy,

Jim