HOW A CONVERTER WORKS

The purpose of any catalytic converter is to reduce harmful emissions from the
exhaust of a "Properly Tuned" combustion engine. It accomplishes this through a
combination of heat and a precious metal catalyst that causes the harmful
emissions to either oxidize or reduce to safe elements in the exhaust flow. If the
engine is out-of-tune and not calibrated to OEM specs, the catalytic converter's
efficiency is greatly diminished and could lead to a converter failure.

The precious metal catalyst is bound to an extruded ceramic honeycomb
substrate. The ceramic has hundreds of flow channels that allow the exhaust
gasses to come in contact with a maximum amount of surface area where the
catalyst reaction takes place. The catalyst must come in direct contact with the
exhaust gasses for the reaction to take place. If the ceramic inside your converter
becomes clogged or coated with carbon, lead or oil, then the converters efficiency
is greatly reduced.

There are three basic types of automotive catalytic converters; Two-Way,
Three-Way and Three-Way + Air. Each type uses a slightly different method and
chemistry to reduce the harmful elements in exhaust emissions. Early model
converters used a pelletized catalyst, but most modern converters are now
designed with a free-flowing honeycomb ceramic catalyst. The type of converter
required on a particular vehicle varies with model year, engine size and vehicle
weight. Some vehicles even make use of more than one type of converter or a
pre-converter to meet emission reduction standards.

Two-Way
Oxidation Converter
A Two-Way converter, used on cars between 1975 - 1980, oxidizes unburned
harmful hydrocarbons and carbon monoxide into water and carbon dioxide. The
first vehicles with catalytic converters had Two-Way reduction only capabilities.
HC, CO OXYDIZES TO H20 and CO2


Three-Way
Reduction/Oxidation Converter
A Three-Way converter is a triple purpose converter. It reduces nitrous oxides
into nitrogen and oxygen. And, like the two-way converter, it oxidizes unburned
harmful hydrocarbons and carbon monoxide into water and carbon dioxide.
NO2 REDUCES TO N2 and 02
HC, CO OXIDIZES TO H20 and CO2


Three-Way + Air
Reduction/Oxidation Converter
A Three-Way + Air converter performs the same functions as the Three-Way
converter. It oxidizes and reduces. The difference is the addition of secondary air
between the two internal catalyst substrates that improves the oxidation
capabilities of the converter. The secondary air is pumped into the middle of the
converter between two seperate catalyst coated ceramic substrates. The front
ceramic performs the reduction and the back ceramic performs the oxydation. Its
like having two converters in one.
NO2 REDUCES TO N2 and 02
HC, CO OXIDIZES TO H20 and CO2


Pre-Converter and Main Converter
Each of the three types of converters mentioned above have a common need in
order to function properly. Each needs to reach a minimum operating temperature
before any emission reduction or oxidation takes place. This warm-up period
immediately after a vehicle is started is when the catalytic converter is least
efficient and the vehicle expels the most pollutants. Some vehicles employ a
pre-converter in the exhaust system immediately after the manifold to help during
this warm-up period. The pre-converter’s small size and proximity to the engine
allow it to heat up and start functioning in less time than the main converter. It also
pre-heats the exhaust gasses and helps the main converter reach operating
temperature sooner.