In this study, the effects of the use of improved fusel oil on engine performance and on exhaust emissions in a spark-ignition engine were investigated experimentally in consideration of the water, gum, and moisture content at high compression ratios according to TS EN 228 standards. In the study, a four-stroke, single-cylinder, air-cooled, spark plug ignition engine with an 8/1 compression ratio was used at three different compression ratios (8/1, 8.5/1, 9.12/1). Experiments were performed for six different ratios of fuel blends (F0, F10, F20, F30, F40, and F50) at a constant speed and different loads. The data obtained from the experiments were compared with the original operating parameters of the engine while using gasoline. According to the test results, the optimal engine performance was at a 9.12/1 compression ratio and with a F30 fuel blend. With the increase from an 8/1 to 9.12/1 compression ratio for the F30 fuel blend, the overall efficiency increased by 6.91%, and the specific fuel consumption decreased by 2.35%. The effect of the optimum fusel blend on the emissions was also examined and CO emissions were reduced by 36.82%, HC emissions were reduced by 23.07%, and NOx emissions were reduced by 15.42%, while CO2 emissions were increased by 13.88%.