Guest Blogger: Street Rod 101
When combustion temperatures get to 2,000 to 2,500 degrees Fahrenheit,
nitrogen is being produced. When this nitrogen mixes with oxygen, nitrogen oxide, referred to as NOx is now created. NOx is considered a form of air pollution and is detrimental to the environment. One method used to reduce nitrogen oxides is to cool down the combustion process. This is done by using an EGR (Exhaust Gas
The EGR valve, as shown in the diagram below, is used to mix small amounts of the exhaust (less than 10%) with the intake. This essentially cools down the combustion. The exhaust gases, which are considerably cooler than the combustion
temperatures, help to cool down the process of combustion.
Looking at the diagram below, the EGR valve has a movable diaphragm in its center. Connected below the EGR diaphragm there is a valve which opens and allows some of the exhaust gases to pass through passagways into the intake manifold. The EGR valve in this diagram is controlled or lifted by a vacuum port on
the carburetor. Note that depending upon the year the engine was manufactured, this control may also be based on the engine coolant. In newer engines the lifting of the EGR diaphragm and valve is operated by an electrical solenoid, controlled by the engine computer.