One-dimensional(1D) simulation tools, the computing speed of which is relatively fast , usually solve simple complexity problems. The solving process of 1D tools is mostly based on one-dimensional dynamic equations and empirical laws and in some cases it cannot obtain a similar accuracy with the three-dimensional(3D) simulation tools, which is usually time-consuming. The 1D-3D co-simulation, which combines the advantages of the two simulation tools while minimizes the disadvantages, is a method that integrates and runs the two simulation tools concurrently. Specially, coupled simulations can offer detailed information where needed 3D domain while offer system level information in the rest of the whole system. The approach not only minimizes the computational cost, but avoids demand for imposing accurate boundary conditions to the 3D simulation. This study describes a detailed analysis of the integrated 1D-3D simulation for different exhaust manifold geometry on a turbocharged gasoline engine. Firstly, the exhaust residual gas fraction of each cylinder was evaluated using 4-1 and 4-2-1 exhaust manifold, respectively. Then, the contribution of the reduced residual gas fraction to the knock index and fuel efficiency was analyzed. After that, the effect of the reduced residual gas fraction on the engine performance was studied under the same knock index. The research results show that the 4-1 exhaust manifold has a larger residual gas fraction due to the more severe pulse interference. The 4-2-1 exhaust manifold can improve the fuel economy of the engine due to the relatively less pumping loss and also attributed to the enhanced combustion efficiency for the fixed engine operating point. The 4-2-1 exhaust manifold can also augment the engine torque by approximately 5% under the same knock index.