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Air injection reactor (AIR) is a very early automobile emissions control system, it reduces the products of incomplete combustion (hydrocarbons and carbon monoxide) by injecting fresh air into the exhaust manifolds of the engine near to the exhaust valves. In the presence of this oxygen-laden air, further oxidation occurs in the manifold and exhaust pipe.

Generally the air is delivered by pump (sometimes called a 'smog pump') driven from a belt off the engine through tubing and valves to the inlet manifold(s). To prevent backfiring a diverter valve is used. When the engine is coasting this valve vents the air to the muffler (silencer) and at high engine speeds allows excess air to escape through a relief valve. Non-return valves prevent exhaust gasses entering then pump.

This technology was introduced in 1966 in California, and was in use for the next several decades. It is not generally in use subsequently, having been supplanted by cleaner burning engines and better catalytic converters.

There is some debate as to A.I.R. effects on the exhaust valves. Some owners claim that the system has kept their exhaust valves clean and prolonged their life, others have blamed them for burning out valves and seats. This appears to trend with the brand and engine configuration, and may be affected by each implementation.

A.I.R. systems have been known to cause exhaust manifolds to glow red (incandesce) due to excess heat.

A.I.R. systems cause increased back pressure in the exhaust. Some engine combinations are more sensitive to this than others, usually higher revving engines or those with high performance cams that include increased valve overlap.

A.I.R. systems do cause some parasitic drag on the engine. but despite criticism from many backyard mechanics, they cause very little loss of engine power, typically around 1-2 horsepower (HP). This amount is unnoticeable except through repeated testing and is incidental to the usual poor tuning in older vehicles. Gains from removal are typically either psychological or due to an improperly maintained system.

• Details with diagrams of the Chevrolet Camaro AIR system www.camaros.org

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