The exhaust manifold is connected with the cylinder block of the engine, and the exhaust gas of each cylinder is collected and guided into the exhaust manifold with branched pipelines. The main requirement for it is to reduce exhaust resistance as much as possible and avoid mutual interference between cylinders. When the exhaust is too concentrated, the cylinders will interfere with each other, that is, when one cylinder is exhausting, it just hits the undischarged exhaust gas from other cylinders. In this way, it will increase the resistance of the exhaust, thereby reducing the output of the engine. The solution is to separate the exhaust of each cylinder as much as possible, one branch for each cylinder, or one branch for two cylinders, and to lengthen each branch as much as possible and shape it independently to reduce the mutual influence of the gas in different tubes.