By the way, one reason I got the HP2 (apart from being such a wicked machine) is that I get to keep the Cat even though I've replaced the exhaust with and Akrapovic, something I could not do with the Dakar without losing the Cat. I do have an environmental bent. The main by-products of combustion are:Nitrogen gas (N2): Our atmosphere is 78 percent nitrogen gas, and most of this passes right through your engine.Carbon Dioxide (CO2): A harmless, odourless gas composed of carbon and oxygen. It is also a greenhouse gas that contributes to global warming.Water vapour (H2O): Another by-product of combustion. The hydrogen in the fuel bonds with the oxygen in the air. These three emissions are mostly harmless, although carbon dioxide emissions are believed to contribute to global warming. However since the combustion process is never perfect, other more harmful emissions are produced in the process.The three main regulated emissions, and also the ones that catalytic converters are designed to reduce, are:Carbon monoxide (CO): A colourless, odourless gas. It is poisonous and extremely dangerous in confined areas, building up slowly to toxic levels without warning if adequate ventilation is not available.Hydrocarbons or volatile organic compounds (VOCs): Any chemical compound made up of hydrogen and carbon.Oxides of nitrogen (NOx): Chemical compounds of nitrogen, they combine with hydrocarbons to produce smog.In order to reduce emissions, modern engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to what is called the stoichiometric point, which is the calculated ideal ratio of air to fuel.Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For petrol engines the stoichiometric ratio is about 14.7:1. This means that for every litre of petrol, 14.7 litres of air will be burned. As engine and driving conditions change, this ratio changes as well. Sometimes it will run richer or leaner than the ideal 14.7:1.You can work it out if you have loads of spare time but the short answer is that if alll of the fuel is burned using all of the available oxygen in the air/fule mix then your bike's catalytic converter does a very good job of removing most of the regulated emissions, BMW claim up to 95% reduction in total emmisons with the use of a converter against an engine without one.Have a great weekend, I'm going riding  😀