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It was presented in the previous paper (1) that oil leakage from valve stem seal (VSS) can be controlled by design and the characteristics of the newly designed composite VSS with a filled polyetrafluoroethylene (PTFE) layer lip are: a constant lower limit of oil leakage, minimal loss of power at low speed due to low friction, extended life over 300,000 km of vehicle traveled distance. It was also reported that oil leakage for lubrication can be determined by the stress distribution across the seal lip contact width touching the valve stem under a certain interference. However, the variable pressure inside Intake and Exhaust ports of an engine will affect the stress distribution of the seal lip causing the change in oil leakage. This report presents the design evaluation method and results of the improved VSS with filled PTFE layer lip which keeps the oil leakage constant even though the inside pressure of the engine port changes.