The increasing number of motorized vehicle users causes increasing air pollution in atmosphere. This condition is due to the exhaust gas content generated by the consumption of this fuel. To resolve this, one of the efforts is to use a mixture of bio-oil in diesel fuel. Bio-oil is a dark brown liquid composed of highly oxygenated compounds produced through pyrolysis, where its properties are close to heavy fuel oil. This study aims to determine the effect of cylinder head variations on the mixture of bio-oil and diesel fuel on the performance of an engine. The engine used in this research is a single-cylinder engine with a direct injection system. When the standard cylinder head variations are used, the best noise, specific fuel consumption, and gas opacity values are obtained. The best noise value is 92.1 dB with a composition of 15% bio-oil and 85% diesel fuel. Meanwhile, the best specific fuel consumption value is 0,236 gram/watt. second with a variation of 20% bio-oil and 80% diesel fuel mixture. The best opacity value is obtained at 30,3% when bio-oil fuel composition is 15% and diesel is 85%.