Usually, there is something outside the exhaust taildrum, which is called "exhaust funnel". Its function is probably known to all, that is, it catalyzes the pollutants in the exhaust gas and makes the exhaust gas cleaner. The modified exhaust taildrum 20 is also located at this position, which seriously affects the exhaust flow rate. Generally, the three-way catalytic converter is a dense honeycomb with 8 to 900 holes (800 meshes and 900 meshes), which can divert waste gas and fully catalyze it. In order to fully catalyze, a condition is needed, that is, a sufficient high temperature, and the closer the drum is to the exhaust valve, the higher the temperature of the exhaust gas, and the easier it is to produce obvious catalytic effect. Most automobile manufacturers, in order to meet the standards more easily for environmental protection, choose the original equipment to be set at the head position close to the exhaust valve. However, in doing so, it is easy for the drum to hinder the smooth discharge of tail gas, and even the back pressure at low speed is too large, resulting in the loss of combustion efficiency.