The purpose of this study is to analyze the effects of variable specific heats of working fluid on the performance of a Dual engine with considerations of heat transfer and friction by using finite-time thermodynamics. The results show that the power output as well as the efficiency where maximum power output occurs will increase with increasing the amount of heat added to the engine due to combustion or with decreasing the quantity of heat loss through the cylinder wall. The temperature-dependent specific heats of working fluid have a significant influence on the performance. The power output and the working range of the cycle increase with the increase of specific heats of working fluid, while, the efficiency decreases with the increase of specific heats of working fluid. Furthermore, the power output and efficiency of the cycle decrease with increasing the parameter b related to the friction loss. It is noteworthy that the effects of heat transfer with considerations of variable specific heats of working fluid and friction loss on the performance of a Dual engine are significant and should be considered in practice cycle analysis.