By combining the high fuel saving areas of these two working modes. the fuel saving map 2/4-stroke switchable secondary expansion internal combustion engine and be obtained, as shown in Fig. 16. The fuel saving rate was over 10% in most working conditions for the 2/4-stroke switchable secondary expansion engine, which could cover most frequently-used condition for a general vehicle engine. The fuel consumption of this new engine was higher than that of the traditional 4RB2 engine only in the low load condition above the speed of 3000 RPM, which is not the commonly used condition. Form Fig. 16, it can also be discovered that the fuel saving rate was higher in the speed below 3000 RPM compared with the high speed conditions, which means the secondary expansion Internal combustion engine based on the burned gas transferring could obtain higher fuel economic performance in the low speed condition.