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The objective of the study was to confirm whether or not it is possible to use the restraint ratio as an evaluation parameter for the thermal fatigue durability of the exhaust manifold. The study revealed that there was a conformity between the thermal fatigue observed in the material experiment and the restraint ratio. The ratio, under certain temperatures, is an effective tool in estimating the thermal fatigue durability of the manifold. An analysis was carried out by regarding the local restraint condition of the exhaust manifold as a spring system. This provided a method where the restraint ratio was reproduced for the manifold under engine operation temperatures of up to 300°C. As a result, the actual restraint ratio can be obtained by performing a relatively simple process. Since the restraint ratios that were calculated correlate with those that were actually measured, quantitative evaluation of thermal fatigue durability using the restraint ratio was found to be possible.