Exhaust gas gas is undesirable, noxious, or toxic substances, such as carbon monoxide (CO) from incomplete combustion, hydrocarbons (properly indicated as CH, but typically shown simply as "HC" on emissions-test slips) from unburnt fuel, nitrogen oxides (NO) from excessive combustion temperatures, and particulate matter (mostly soot). Exhaust gas temperature (EGT) is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge. EGT is also a measure of engine health in gas-turbine engines (see below). During the first two minutes after starting the engine of a car that has not
Exhaust system tandem with smog abatement legislation rendered lake pipes, as a bona fide performance prerequisite, obsolete. No meaningful performance gain to be had for contemporary vehicles, lake pipes persist into the 21st century as a superfluous, retrograde aesthetic, usually chrome plated with various options, allowing the driver to control whether exhaust gas is routed the standard exhaust system, or through lake pipes, which are commonly fashioned by laker caps which, affixed by fasteners at the terminal end of exhaust tips, serve to (1) "cap" the exhaust system when not in use, and/or (2) signal authorities that the presence of lake pipes