The concept of double compression, and double expansion stages (DCEE) for improving the efficiency of piston reciprocating engines was introduced in SAE Paper 2015-01-1260. This engine configuration separates high, and low pressure units thereby effectively reducing friction losses. The presence of an additional expander stage also allows an extra degree of freedom to manipulate the combustion heat release rate so as to achieve better optimum between heat transfer, and friction losses. This paper presents a 1-D modeling study of the engine concept in GT-Power for assessing the sensitivity of engine losses to heat release rate at a given speed-load point. The simulations were constrained by limiting the range of maximum motoring pressures from 200 bar to 300 bar, and the maximum pressure during combustion to 300 bar. The maximum motor pressure was varied by constraining the compression ratio of the high pressure unit and adapting the low pressure unit accordingly. The end of combustion was constrained to 20°, 40°, 60°, and 80° ATDC.