The manufacturing process of the exhaust valve in large marine diesel engines consists of an upset forging and final forming process. In the past, the exhaust valves in large marine diesel engines have been made through free forging by using the stretch forming method. This method has used the ingot and the billet as a preliminary forming process. Nimonic 80A, a superalloy, is presently used for the material of the exhaust valve. For the forming method of the valve, the electric upset method is used. Solid bar is raised up to the forming temperature by using electric energy and is continually deformed by upset pressure. The electric upsetting processing is a useful method for the high quality of exhaust valves in large marine diesel engines. It can keep the continuous grain flow, excellent mechanical property, and corrosion resistance because of the elaborate macrostructure of the valve face. The purpose of this paper is to predict the optimum process condition through simulation of the exhaust valve with a diameter of 73mm. The experimental result of an exhaust valve with a diameter of 19mm is in good agreement with the simulation result using the "QForm" that can solve electric upsetting problems. Finally, the optimal manufacturing process of the electric current and the upset load are surveyed.