The G-CAT Catalytic Converter is a closed loop catalytic converter fitted to BMW motorcycles as standard. In this system, digital engine electronics ensure that exhaust gas levels are well below the legally required norms. Engine management functions are performed by an interactive regulatory system consisting of Motronic, the catalytic converter, and the oxygen sensor. This system works effectively to reduce pollutant levels in the exhaust gas. A metal based catalytic converter using precious metals such as palladium and rhodium on its surface is used to cleanse the exhaust gas. These catalytic precious metals convert harmful substances such as carbon monoxide, hydrocarbons, and nitrogen oxides into harmless ones. The key to the effectiveness of the catalytic converter is the proportion of air to fuel in the combustion process. A proportion of 14.7 parts air to one part fuel is ideal. The oxygen sensor measures the residual oxygen content in the exhaust gas and thus provides the control unit with the data it needs for the composition of the air to fuel ratio. This ensures appropriate exhaust levels for long term environmental protection. A closed loop catalytic converter with its attractive sound is installed in high quality exhaust systems. This makes it the optimum choice, from both a general and environmental perspective.