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Technically, if the piston were to go faster than the speed of sound, it would create a shock wave in the chamber. However, this is not going to happen, for many different reasons. First, the force needed to move the piston up and then have it change direction would quickly destroy the inside of the piston engine. The energy lost through friction could reach dangerous heats. Then, as the piston moves nearer the speed of sound, it would begin developing a vacuum just behind it, which would make it more difficult to pull the piston up.