The compression ratio is what determines the correct octane . General guidelines for all 2 and 4 strokes are as follows ( Turners Tuners hand book)
Compression Ratio / Octane #
8.0- 8.5 ..... 87-89
9.0-9.5 ..... 90-91
10.0-10.5 .... 91-93
Most GY6 motors are in the 8.5 to the 9.5 for a stock motor. If you dont know what it is then you have to CC the head .
Last edited by rich1; 04-18-2013 at 04:19 PM.
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