What do they do?

Catalytic converters reduce the levels of polluting toxic gases expelled as exhaust gas from the engine combustion chambers prior to being expelled through the exhaust. Currently tested for during annual MOT are; carbon monoxide, hydrocarbons, nitrogen oxide, and particulate mass. Regulations allow for variances, so have a range of acceptable measures. Making automotive emissions less harmful is a big priority for a more environmentally conscious society, making regulatory changes in this area a real possibility.

How do they function?

The exhaust gas is catalysed by a redox reaction; platinum initiates the oxidation process of carbon monoxide to carbon dioxide, followed by rhodium completing the reduction reaction of nitrogen oxides into nitrogen and oxygen. During the 1980s three-way catalytic converters (as described above) became standard in the automobile industry, as remains the case today.

Should I upgrade?

Catalytic convertors can be damaged by unburnt fuel when running too rich, oil consumption due to piston rings fail, or coolant leaks due to a head gasket fail. If damaged the internal components can cause a rattling sound which will deteriorate with time. Most stock catalytic converters are inefficient, detrimental by up to three percent of engine power. Installation of a modern, more efficient catalytic converter can reduce this power loss to around one percent.