Liquid-cooled engines are quieter than air-cooled engines, and the engine of the PCX takes this benefit to the next level with several noise-reducing technologies. At typical urban cruising speeds, the engine of the PCX reduces rpms while producing maximum torque—approximately 16 percent more torque than a 125cc air-cooled engine. For example, at 60 km/h on level ground, the PCX runs at 300 rpm lower than the Spacey 125. Reduced rpms mean reduced engine noise and vibration, resulting in a ride that is more refined than that of previous 125cc scooters.
For additional quietness during startup, the PCX is the first 125cc scooter to feature an ACG starter, which is controlled by an ECU (Electronic Control Unit) and serves as both a starter motor and an alternator. After starting up the engine of the PCX, the same device immediately begins serving as an alternator. The ACG eliminates the cranking noise associated with startup, resulting in exceptionally quiet starts. Idle stop function* further enhances quietness and fuel economy by automatically stopping the engine after the rider stops the vehicle at traffic signals and in similar situations.