Corvette C3 Emission Systems

Emission regulations for cars were tightened in the 1970s, which also impacted the development of the Corvette. Various methods were developed to reduce emissions. California's pioneering efforts to combat air pollution were particularly evident in the Corvette C3 generation, where slightly different technical solutions were offered for the California market over several years.

The stricter emission standards also led to a reduction in engine power. For example, the base model of the 1975 Corvette produced only 165 horsepower. Some states or cities do not impose emissions requirements on older vehicles, which is why many Corvettes have had these “horsepower-robbing” systems removed.

Car emissions have frequently made headlines in recent years, alongside discussions about upcoming bans on new internal combustion engine vehicles. Classic cars, however, are typically driven only a limited number of miles each year, resulting in relatively low overall emissions. The development of synthetic fuels could further secure the future of these vehicles. Nevertheless, the emission control systems introduced in the 1970s continue to effectively reduce emissions in surviving classics 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.

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.

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.

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.

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