It is essential to keep in mind that the analysis here is based on the premise that the temperature ratio represents the temperature extremes of the working gas. Because of heat transfer limitations, the gas temperatures will always be closer together than the temperatures of the metal surfaces of the heat exchangers. This makes the actual gas temperature ratio ? larger than the ratio of the cold-to-hot end surface temperatures. This temperature ratio discrepancy becomes more pronounced at higher engine speeds. This needs to be taken into account when choosing the swept volume ratio for an engine design. The optimization table shows that as the effective gas temperature ratio ? increases, the optimal swept volume ratios are lower. Once again the general advice that emerges is to favor a swept volume ratio lower than ?*. Again, how much lower depends upon how effective the heat exchangers are and how fast the engine will be run.