Corvette C3 emission systems 1968 - 1982

Emission restrictions

Emission restrictions for cars were tightened in the 1970s, which was also reflected in the development of the Corvette, different ways were developed to reduce emissions. California's pioneering effort to reduce air pollution was also seen in the cars of the Corvette C3 generation, for several years slightly different technical solutions were offered to California to reduce emissions.

The stricter emission restrictions also meant a reduction in engine power, the base model of the 1975 model produced only 165 hp. Some states or cities do not have emissions regulations for older cars, and for this reason, many Corvettes have been stripped of these “horsepower-robbing” systems.

Car emissions have been in the news a lot, as has the banning of new combustion engine cars in the near future. Classic cars are often driven relatively little per year, so the emissions are therefore not very high and possible synthetic fuels can save the future of classic cars. However, these systems developed in the 70s still reduce car emissions even today.

Air Injection Reactor (AIR) aka "smog pump"

The air injection system works by introducing fresh air into the exhaust system at all engine speeds, but bypasses air briefly during deceleration and at high speeds, preventing backfiring through the exhaust. The additional air reacts with unburned hydrocarbons and carbon monoxide present in the exhaust gases, converting them into carbon dioxide and water vapor, which are much less harmful to the environment.

The AIR system consists of an air pump (smog pump), valves, hoses, and air injector tubes that direct fresh air to the exhaust manifold.

Exhaust Gas Recirculation (EGR)

The Exhaust Gas Recirculation (EGR) system works by recirculating a portion of the engine's exhaust gases back into the intake air stream. The recirculated exhaust gas contains inert gases, such as carbon dioxide and water vapor, which help to cool the combustion process and reduce the amount of nitrogen oxides (NOx) released into the atmosphere.

The EGR system consists of a vacuum-operated valve that admits exhaust gases to the intake manifold, a hose connected to the carburetor above the throttle valve, and a thermostatic vacuum switch (TVS). When idling, the throttle plate blocks the vacuum port, so the vacuum cannot reach the EGR valve and it stays closed. Under acceleration, the vacuum opens the EGR valve, allowing the exhaust gases to circulate into the intake manifold, but only when the engine is at normal operating temperature because the TVS only lets the vacuum through then.

Positive Crankcase Ventilation (PCV)

The PCV valve is located on the engine's valve cover and controls the flow of blow-by gases into the intake system. The valve is designed to regulate the amount of gases flowing into the intake system based on the engine's operating conditions.

When the engine is operating, a partial vacuum is created in the intake manifold. This vacuum draws blow-by gases from the crankcase, through the PCV valve, and into the intake manifold. The blow-by gases are then mixed with the fresh air/fuel mixture and burned in the combustion chamber, reducing the emissions of harmful pollutants, such as hydrocarbons and carbon monoxide.

In addition to reducing emissions, the PCV system also helps to prevent crankcase pressure buildup, which can lead to oil leaks and other engine problems.

Year	PCV usage
1968 - 1982	All Corvettes

Evaporation Control System (ECS)

The Evaporative Emission Control System (ECS) is a closed fuel system used to reduce the amount of fuel vapors. The ECS reroutes wasted fuel back to the fuel tank and stores fuel vapors instead of venting them to the atmosphere. If the fuel system is not sealed, fuel vapors are constantly released even if the car is not driven. The ECS was introduced in 1970, and it was required for California buyers, in 1971 for all Corvettes.

The ECS consists of a sealed fuel tank/cap, a charcoal canister, and a series of hoses and valves. Vapors from the fuel tank go into a charcoal canister, which has a filter at the bottom. When the engine is running, stored fuel vapors are drawn into the intake manifold and burned in the combustion chamber.

Year	ECS usage
1968-1969	No
1970	Only California
1971-1982	All Corvettes

Early Fuel Evaporation (EFE) / Heat riser

The Early Fuel Evaporation (EFE) and heat riser systems shorten the engine's warm-up time and thus reduce hydrocarbon emissions. The EFE system consists of a valve in the exhaust manifold, an actuator, and a thermal vacuum switch (TVS). The EFE was introduced in 1975.

The TVS lets vacuum through only when the engine is cold, and the vacuum is applied to the actuator, which closes the EFE valve and routes the hot exhaust gases to the base of the carburetor. In pre-1975 Corvettes, a heat riser handled the same thing, where the valve was controlled by a bi-metallic spring.

Year	Heat riser / EFE usage
1968-1974	Heat riser
1975-1982	EFE

Catalytic converter

A catalytic converter is a device used in the exhaust system of vehicles to reduce the amount of harmful pollutants emitted into the atmosphere, and it was introduced to all Corvettes in 1975.

The main function of a catalytic converter is to convert toxic gases and pollutants, such as carbon monoxide, nitrogen oxides, and unburned hydrocarbons, into less harmful substances like carbon dioxide, nitrogen, and water vapor. The converter works by using a catalyst, usually made of platinum, palladium, or rhodium, which is coated onto a ceramic honeycomb or other substrate. When the exhaust gases pass over the catalyst, a chemical reaction takes place, which breaks down the harmful pollutants into less harmful components.

Year	Catalytic converter usage
1968-1974	No
1975-1982	All Corvettes

Parts

Some spare parts related to emission systems are difficult to find since not all of them have been reproduced. You can contact Corvette Parts Central, they have a wide range of new, used, and reproduction Corvette parts.

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