Considering the growing concerns about the depletion of fossil fuel resources and air pollution, the investigation of alternative fuels with cleaner combustion has gained importance. In this study, the effects of gasoline–n-butanol blends on the performance of the Iran National Engine were experimentally examined. The tests were conducted under controlled laboratory conditions at engine speeds of 2000, 2500, and 3000 rpm and four load levels of 25, 50, 75 and 100 percent. The tested fuels included pure gasoline and three blends NB5, NB10 and NB15 containing 5, 10 and 15 percent by volume of butanol, respectively. The results showed that at full load and 3000 rpm, the NB15 blend increased torque by 13.7% and brake power by 12.4% compared to pure gasoline. At medium loads, the NB10 blend exhibited the most stable combustion and a more uniform torque output. Additionally, the addition of butanol reduced exhaust gas temperature by approximately 4 - 5 percent, indicating more controlled combustion and reduced thermal stress on the engine. The observed performance improvement is attributed to the higher octane number, the presence of oxygen in the molecular structure, and the high heat of vaporization of butanol, which lead to a more homogeneous mixture and enhanced flame stability. The results indicate that using fuels containing 10% and 15% n-butanol can effectively improve combustion quality and engine power, representing a step toward the development of sustainable and efficient fuels.