Computer simulation studies are currently underway for the proposed FEL amplifier experiment to be carried out using the existing 38 MeV, L-band linac based FIR FEL system at the Institute of Scientific and Industrial Research (ISIR), Osaka University. This paper describes the time-dependent and time-independent simulation results using Genesis code. Dependence of FEL amplifier characteristics are investigated such as the power spectrum and profile, frequency spectrum and FEL bunching parameter on parameters like the beam current, input power and interaction length. The operating current regime and input seed laser powers required for the optimum amplification are given.