In this paper, it is presented a useful combination with recently proposed criterion, Mean Cycle Pressure (MCP), and Entropy Generation (EG) for thermodynamic optimization of commonly used basic power cycles (Otto, Diesel and Atkinson). The thermodynamic performance of a system and physical size are both optimized together with proposed criterion which aims to maximize thermodynamic performance or net specific exergy of cycle to a specified size that characterized as minimum and maximum specific volumes of cycle. The analyses are based on the variations of compression ratio and the ratio of maximum temperature to the minimum temperature. The results show that, in terms of EG, Otto cycle can reach the highest efficiency and MCP values using the lowest compression ratio. Although Otto cycle has the lowest compression ratio, it has also the lowest thermal efficiency at maximum MCP conditions with the achievement of reaching 2 or 3 times smaller dimensions. Beside this, the compression ratio that maximizes the MCP is the lowest for Otto cycle. On the other hand, increasing of the temperature ratio for a constant compression ratio increases the MCP and EG and increasing of the compression ratio for a constant temperature ratio maximize the MCP for all cycles. At maximum MCP conditions, the smaller thermal systems or power cycles may be designed in response to a slight increase in entropy generation and a slight decrease in thermal efficiency. From the analyses it can be viewed that proposed criterion is appropriate for thermal system optimization for different purpose of using and will give important constraints and criteria to the designers and engineers.