In order to move towards higher level of technology and to face advanced challenges, Thunder Tiger started its R & D of model four- stroke engines. After the important breakthrough of key accessory developments, the first Thunder Tiger made four-stroke model engine, F-91S, took the global. Its classic appearance with outstanding quality, high performance, low noise, and less pollution offer a more fresh and serene environment for the industry. Thunder Tiger four-stroke engine- F-91S adopts the designs of pent- roof combustion chamber and single-ring which highly improved the efficiency of volumetric and compression. Due to the complete manufacturing design under strict ISO 9001 quality control system, all of the engine parts are able to meet the highly-precise quality requirement. Inside its splendid features, the engine can also produce high-performance power output. The successful development of four stroke engine leads Thunder Tiger an advanced field where the company will keep the spirit of research and innovation to strive constantly for perfection towards higher goal.