Because of reduced displacement volume and inherent stoichiometric operation of downsized turbocharged gasoline direct injection engine. torque and power decrease and transient response delay problems have been pointed out. In this paper, effect of turbine wheel inertia and ignition timing on transient response and combustion were studied using 2.0 L downsized turbocharged GDI engine equipped with TiAl(Titanium Alluminide Alloy) and Inconel turbine wheel turbocharger.