New 12V/48V power net architectures are potential solutions to close the gap between customer needs and legislative requirements. In order to exploit this potential an increased functional implementation and hardware integration effort is needed. Shifting of development tasks to earlier phases (frontloading) is a promising solution to streamline the development process and to increase the maturity level. This study shows the potential of a virtual 48V mild hybridization architecture together with the frontloading of development tasks by implementing virtual hybridization in an Engine-in-the-Loop(EiL) setup. Advanced simulations technics like Functional Mock-up Interface (FMI) based co-simulation are utilized for the seamless integration of the real time models and allow a modular simulation framework and a decrease of the development time. As base line, an existing and validated co-simulation consisting of a GT-POWER engine model, a SimulationX transmission model and a dSPACE ASM vehicle dynamics model is used. A Simulink-based dual 12V/48V power net model extends the base model. The 48V side is mainly composed of a belt driven starter generator (BSG) directly connected to the combustion engine (P0-layout) and a 48V Li-battery. The 48V side is coupled via a bidirectional DC/DC to the 12V AGM-battery and the 12V loads. In the next step an engine test bench is coupled with the real time simulation by replacing the simulated combustion engine. Extensive tests are carried out on the Engine-in-the-Loop test bench considering new legislative test requirements like WLTC and RDE. The results show the great emission potential of 48V mild hybrids and proof that 48V is a possible solution to close the gap between customer needs and legislative requirements.