Catalytic Converter: Debuted in 1975. These devices get red hot on the inside and essentially burn the carbon monoxide and hydrocarbons left over from the engine’s combustion process. They are also known simply as a ‘catalyst’.
‘Pelletized’ was the early style of catalyst. Exhaust gases flow through thousands of pellets which are coated with platinum and palladium. This style genuinely snuffs horsepower, as much as 20 or more on the average 70s car.
‘Screen’ style was the later version which is still used on modern cars. Instead of pellets there are layers of screens inside. The screens themselves are coated with the platinum and palladium. This style creates less backpressure and doesn’t decrease horsepower much on a street car.
Leaded fuel will destroy a catalytic converter. This is why ’75 and up American cars also have a fuel inlet restrictor on the gas filler neck that allows the nozzle from only an unleaded fuel pump to fit.
Back in the day, it was a popular modification to remove the catalytic converter and fuel inlet restrictor on cars just to be able to save money by using cheaper leaded fuel. This change became obsolete when leaded fuel was discontinued in the U.S.