Royal Enfield is more than a motorcycle to many in India. It is a lifestyle, a cult following that has come a long way since the beginning. If you care about your bike and the environment, please do not change the silencer ever! The stock silencer of Royal Enfield is designed to create back-pressure in the engine that helps in complete combustion of the fuel and noise reduction. Changing it will definitely reduce the mileage of the bike and increase air pollution.