T-304 stainless steel, TIG welding, limited life guarantee, stainless steel mesh wrapped hole core, high-quality glass fiber packaging, and all double 3.5 ″ round coil silencers are installed on the air duct. Due to the friction of the inner wall of the muffler, the sudden change of the cross section of the elbow, perforated plate and pipe and the sound-absorbing material, the aerodynamic characteristics of the machine will be affected. Excessive resistance will significantly reduce the power consumption or output energy of the internal combustion engine, and even make the machine unable to run. Resistance loss is an index to evaluate the aerodynamic characteristics of muffler.