The main use of FRC in automobiles, with the exception of a few specialized low volume vehicles, has been until now in semistructural parts. One of the most promising process in development today, that may play major role in future structural composite fabrication, is based on SRIM technology. The rapid and extensive introduction of this process goes also through the development of deeper theoretical knowledge of the process and the development of computer simulation to aid mold design and choice of proper processing parameters. To contribute SRIM advancement, a preliminary model has been developed for viscosity changes, extent of the reaction and temperature rises, associated with the mold filling stage, as well as a simple software to evaluate the pressure drop through different combinations of reinforcements. The model is able to satisfactorily verify the variations of all the key process parameters (i.e. the amount and type of reinforcement, the injection time, the catalyst level, temperatures). In each simulation the groups of the relevant dimensionless numbers have been identified and their values have been utilized as moldability criteria.