Government required emission regulations.
catalytic converter
In UK, all new cars from 1992 had to have a catalytic converter fitted, which required a strict diet of unleaded fuel. Many had 'cats' fitted as standard well before then.
All cars made since 1975 in America have a catalytic converter.
The main usage of a MagnaFlow Catalytic Converter or any other catalytic converter is commonly the reduction of toxic emissions in the exhaust systems in cars.
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No, diesels can and do have them also.
Absolutely not. The fumes released from any engine can be deadly without a catalytic converter and severely harm the environment no matter how efficient the engine is and no car can legally not use a catalytic converter.
Because that is how they are made to run. They were added to cars to cut smog emissions and meet federal/state standards. Lead ruins the catalyst in the converter.
Almost all cars have only one catalytic converter. Some can have two, four, etc.
to limit the air pollution the car puts into the atmosphere.
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If your question is "Does a diesel car have a catalytic converter" then I might be able to help. Some countries require catalytics on diesels, and some US states also require them. Most newer cars and trucks will have them mounted. A diesel engine will actually run better without a catalytic, but having one will cut down on the black soot coming out of the exhaust pipe. California I know for sure will start to require smog checks on diesels. one way to automatically fail is if you have removed your catalytic converter. I've owned several diesel trucks...