What is EGR for?

[SwissJeeper]

What exactly does EGR do? Does it affect idle-smog? Can I use an Edelbrock 1400 (EGR) carb on an Edelbrock Performer 2131 (non-EGR) manifold?

[BobBarry]

The EGR should be closed at idle (by-design), so it should not affect idle emissions. It replaces some of the oxygen-rich intake charge with inert exhaust-gas, which allows means you can calibrate the carb leaner (less air requires less fuel). It does NOT reduce intake-charge temperatures (I'd like to see somebody explain how hot exhaust can cool the incoming air...), but it reduces combustion-temperature temps, simply because the engine is burning less fuel, which puts out less energy.

It is a type of "variable-displacement" mechanism, but rather than reducing the engine's displacement mechanically, it does so pneumatically.

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Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[Shane]

Bob is right on what he said and the reason it is used is because a high combustion temp emits oxides of nitrogen, lowering combustion temp. reduces these NOx(x being variable)

Its all about emisions.
Shane

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1982 J10 Model 25 Pioneer
My Daily driver since 1988
D44,258(.030" over),T5,NP208,AMC20

[Ralph]

Bob's right, nothing to add. However, I'd like to point out that atomized fuel being drawn in through the intake manifold passages does in fact cool the intake manifold. The effect is called latent heat of vaporization, similar to the principles that govern air conditioning.

Carburetors and TBI systems are called "wet flow" fuel delivery systems because of this. In contrast, "dry flow" fuel delivery systems such as MPI must often cope with higher intake manifold temperatures because only air is flowing through, and no atomized fuel to cool the runners. A thermal barrier coating such as Jet-Hot applied to the bottom of the manifold has proven to be beneficial.

[This message has been edited by Ralph (edited December 19, 2000).]