The demand for injection molded reinforced plastic products used in the automotive industry is growing due to the capability of the material for volume production, high strength to weight ratio, and its flexibility of geometry design. On the other hand, the application of fiber filled plastic composites has been challenging and subject of research during past decades due to the inability to accurately predict the mechanical strength and stiffness behavior owing to its anisotropic characteristics. This paper discusses a numerical simulation based technique using multiscale (2 scale Micro-Macro) modeling approach for short fiber reinforced plastic composites. Fiber orientation tensors and knit lines are predicted in microscale analysis using Autodesk Inc.’s Moldflow® software, and structural analysis is performed considering the homogenized structure in macroscale analysis using ANSYS® software tool. This approach accurately captures the stiffness and stress behavior of reinforced plastic materials. Further, a case study is discussed with application of developed approach on reinforced plastic supercharger couplings which are used to connect two coaxial shafts for torque transfer. It is observed that critical locations in couplings are high stress regions with undesirable fiber orientation and presence of knit lines, which further reduced the strength of the coupling. Modification of gate location is recommended to improve fiber orientation and change in location of knit lines, in order to increase the coupling strength which is verified numerically and through testing using this developed approach.