The Sources of the Pollution Problem
The basic problem with the internal combustion engine is that it emits a number of pollutants in the process of producing power, such as:

Hydrocarbons-these emissions result when the engine does not burn all the gasoline taken in. Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, a major component of visible smog.

Nitrogen Oxides (NOx)-created by high-temperature combustion, nitrogen and oxygen atoms form NOx. Like hydrocarbons, they contribute to ozone and the formation of acid rain.

Carbon Monoxide (CO)-a product of incomplete combustion and occurs when carbon in the fuel is partially oxidized rather than converted to carbon dioxide (CO2).

Carbon Dioxide-in recent years, the U.S. Environmental Protection Agency (EPA) has started to view carbon dioxide, a product of "perfect" combustion, as a pollution concern. Carbon dioxide does not directly impair human health, but has been labeled as a "greenhouse gas."

Evaporative Emissions-Hydrocarbons also escape into the air through fuel evaporation from a variety of sources including the fuel tank and carburetor as well as during refueling.

The Cures
When smog control devices first appeared most performance enthusiasts became convinced the end of life as we knew it was near. Although catalytic converters were touted to significantly reduce hydrocarbon and carbon monoxide emissions, they were restrictive-on some engines the effect on performance was like hammering the tailpipe closed. To add to the problem, with the unleaded gas catalytic converters required, the lifespan of exhaust valves became shorter and it appeared the naysayers were right. However, technology eventually came to the rescue once again. Manufacturers stepped up and began using better materials for valves and seats and consumers began to notice that parts like spark plugs and exhaust systems lasted longer without lead in the fuel. Maybe things weren't so grim after all.

By 1980 more sophisticated emission control systems came along including the "three-way" catalytic converter, which turned carbon monoxide and hydrocarbons to carbon dioxide and water and also helped reduce nitrogen oxides to elemental nitrogen and oxygen. And to top it off, these new converters didn't restrict flow like the earlier versions, so many performance vehicles had that beloved rumble out of the exhaust pipes once more. But the big reason emissions systems have become more effective and we have better performing powerplants in terms of horsepower, mileage, and longevity is directly attributable to the sophistication of today's computer controlled engine management systems. Let's face it, nothing looks cooler than a small-block with a handful of carburetors and a magneto, but nothing runs better than a new LS series engine with computer controlled fuel injection and electronic ignition.

A contemporary automotive Electronic Control Module (ECM) makes continuous changes to the engine's state of tune with information from a variety of sensors such as:

Mass Airflow (MAF) Sensors-measures the volume and density of air entering the engine. The computer uses this information in conjunction with input from other sensors to calculate the correct amount of fuel to deliver to the engine, as well as ignition timing.

RPM/Crank/Cam Position Sensors-used to control ignition timing.

Manifold Absolute Pressure (MAP)-for altitude compensation and load correction.

Coolant Sensor (CTS)-monitors operating temperature for fuel/spark adjustments.

Manifold Air Temperature (MAT)-monitors intake air temperature.

Throttle Position Sensor (TPS)-feedback for fuel control.

Knock Sensor-detects and protects the engine from detonation and adapts the system to octane levels.

Pre-Catalyst Oxygen Sensors-controls A/F ratio.

Post-Catalyst Oxygen Sensors-performs catalyst diagnostics.