Lean mixture operation and high transient response has been accomplished by the introduction of newly designed Central Injection (Ci) system. This paper describes the effects of Ci design variables on its performance. Lean mixture operation has been attained by optimizing the injection interval, injection timing and fuel spray angle in order to improve the cylinder to cylinder air-fuel ratio distribution. Both air-fuel distribution and transient engine response are affected by the fuel spray angle. Widening the fuel spray angle improves the air-fuel distribution but worsen the transient engine response. This inconsistency has been solved by off-setting the injector away from the center axis of the throttle body and optimizing the fuel spray angle.Applied to 1.8L 4-cylinder engine FWD vehicles, this new Ci system gives 10% improvement in fuel economy in the Japanese 10 mode driving cycle over a conventional stoichiometric feed back carburetor system, and keeps satisfactory driveability and NOx emissions.