Caveat: The various systems described here and on linked pages are generic in nature and NOT specific to a particular make/model of Chevrolet. You need to consult your Chevrolet's service manuals for particulars.

Prior to emission standards, the crankcase was vented to the atmosphere.

Draft tube and ventilator on an early small block Chevrolet V8 engine. The ventilator was attached to the engine block under the intake manifold to collect crankcase fumes and was vented to the outside atmosphere via the draft tube.

Over the years various attempts have been made to control exhaust emissions. In 1958 the Positive Crankcase Ventilation (PCV) system was introduced as standard equipment on the 348cid Chevrolet engines in heavy trucks.

In 1966, California introduced stricter emission standards for vehicles built in (or to be sold in) the state. Thus, the Air Injection Reactor (AIR) system was born.

An alternative to the A.I.R. system, the Controlled Combustion System (CCS) introduced in 1968 on some engine/transmission combinations was used.

In 1968, Chevrolet introduced the Carburetor Heated Air (CHA) system to help improve fuel economy and eliminate carburetor icing.

The Transmission Controlled Spark (TCS) system was introduced in 1970 and had some variances in 1971 and 1972.

First introduced in 1970 for vehicles sold in California, the Evaporation Control System (ECS) was mandated in 1971 for all cars and trucks under 6,000 pounds to be equipped with such a system.