Exhaust Glossary
Back pressure: Resistance of an exhaust system to the passage of exhaust gases. This can have an adverse effect on performance, fuel economy, and emissions. Excessive back pressure may be caused by a clogged catalytic converter, or a dented or crimped pipe.
Baffle: A barrier used to reduce noise in an enclosed system, such as the exhaust system.
California Air Resources Board (CARB): A California agency responsible for regulations intended to reduce air pollution, especially that created by motor vehicles.
Cat: An abbreviation for catalytic converter.
Catalytic converter: An automotive exhaust-system component, made of stainless steel, containing a catalyst to reduce oxides of nitrogen (NOX), and/or hydrocarbon (HC), and carbon monoxide (CO), in tailpipe emissions.
Collector: A device that collects exhaust gases from the primary tubes and channels them into a single exhaust pipe.
Dual exhaust: An exhaust system used on V-type engines with a separate muffler, exhaust, and tail pipe for each cylinder bank.
Dump tubes: Straight through exhaust headers.
Emissions: Unwanted, harmful chemicals and chemical compounds that are released into the atmosphere from a vehicle, especially from the tailpipe, crankcase, and fuel tank including unburned hydrocarbons, carbon monoxide, oxides of nitrogen, particulates, and sulfur.
Equal length headers: An exhaust system having equal length tubes from each cylinder to the collector.
Exhaust analyzer: An automotive test and service device that uses a process involving infrared energy to determine and display the composition of an engine's exhaust gases such as the two-gas type to measure hydrocarbons and carbon monoxide or the four-gas type, which also measures oxygen and carbon dioxide.
Exhaust back pressure: The resistance of the free flow of gas in the exhaust system.
Exhaust emissions: Pollutants identified by clean-air legislation as being harmful or undesirable, including lead, unburned hydrocarbons, carbon monoxide, and oxides of nitrogen.
Exhaust gas: The burned and unburned gases that remain after combustion.
Exhaust headers:
- A term used for exhaust manifold.
- A special exhaust manifold with tubes of equal length from the exhaust ports to the header of the exhaust system.
Exhaust manifold: A component, generally of cast iron, with passages of unequal lengths that carry the exhaust gases from the exhaust ports to the header of the exhaust system.
Exhaust pipe: A pipe that connects the exhaust manifold, the muffler, or catalytic converter.
Exhaust system: The tubing, mufflers, and catalytic converters that direct exhaust gases from the engine to the atmosphere.
Free-flow exhaust: An exhaust system with reduced back pressure.
Header: A free-flowing exhaust manifold used on high-performance cars.
Lambda:
- A term used by engineers to represent the air/fuel ratio.
- A European auto maker's term for the oxygen sensor.
Laminar airflow: The smooth, continuous movement of one layer of gas or liquid over another.
Lean mixture: An air/fuel mixture with too much air.
Muffler: A device in the exhaust system used to reduce noise.
Muffler bearing: A non-existent part.
Muffler clamp: A clamp that secures the muffler, or pipe, to the bracket or hanger.
Muffler hanger: A hanger that is used to secure the muffler.
O2 sensor: A term used for oxygen sensor.
Oxygen sensor: A device found in the exhaust manifold, which generates a small voltage dependent on the amount of oxygen present in the exhaust stream, used as a signal to the engine-control computer to determine the amount of fuel necessary to maintain a proper air/fuel ratio.
Resonator: A small auxiliary muffler, after the main muffler, used to help reduce engine noise without restricting the flow of exhaust gas.
Safety wire: A strong wire, usually stainless steel, used to hold pre-drilled nuts or bolts in place, preventing them from turning.
Secondary air: Air that is pumped to the pollution-control devices to promote chemical reactions that reduce exhaust gas pollutants.
Silencer: A device, such as a muffler, designed to reduce noise.
Skin effect: A thin, unburned layer of air/fuel mixture next to the combustion camber surface.
Try-Y headers: An exhaust manifold setup that pairs cylinders according to their firing order to provide better exhaust scavenging.
Tuned exhaust: An exhaust system having equal length passages.
Y-pipe: A Y-shaped pipe, such as an exhaust pipe, that merges two passages into one.
