Abstract: An air swirling device comprises a pipe member connected in between an air cleaner and an internal combustion engine; a plurality of swirl-flow ducts spirally formed in the pipe member; and a central-flow duct axially formed in the pipe member and surrounded by the swirl-flow ducts; with each swirl-flow duct being formed by a swirl plate spirally secured to an inside wall of the pipe member and juxtapositionally partially linked to each adjacent swirl plate; whereby upon suction by the engine, the inlet air will be guided and swirled by the plural swirl-flow ducts to form swirling air flow, as accompanied with a central air flow through the central-flow duct, for homogeneously mixing fuel with air for enhancing a complete combustion of fuel to thereby increase the engine performance. The air whirling device may also be modified to be installed between the engine and an exhaust or tail pipe.