Octane number is a reference to measure quality of gasoline as the fuel of gasoline engine. Gasoline with higher octane number gives less tendency to knocking. Naphtalene is a chemical solution that gives positive effect to rise the octane number. Octane number of gasoline can be measured by CFR engine. Using a motor Daihatsu CB-23, the best power obtained by using a grain of naphtalene (3,75 grams) for 3 litres of gasoline and ignition timing is 12° before TDC. Using this ratio, CO & CO2 that are produced in the exhaust gas is nearly the ame with pure gasoline usge but less HC and O2 are produced.