An air connector is described mountable opposite an intake or exhaust port in an associated intake or exhaust pipe of an internal combustion engine to allow the port to communicate selectively with the associated pipe and with a compressed air storage tank. The connector comprises a stopper mounted on a rod movable by an actuator between an open position in which the port communicates with the associated pipe and a closed position in which the stopper seals around the entrance of the port to isolate the port from the associated pipe. An air passage is provided in the stopper and the rod to allow communication between the port and the compressed air storage tank when the stopper is in the closed position, and a check valve is arranged in the air passage and biased in a direction to prevent escape of air from the compressed air storage tank in all positions of the stopper.