Exhaust gas is inert and doesn't burn like air/fuel. EGR comes on at cruise and puts a layer of inert gas in the cylinder which in turn allows less room for air/fuel mix which means a smaller flame which in turn lowers combustion chamber temps and NOx emissions. This is pretty much the reason it only comes on at cruise, and will stall a car if it opens at idle. This is how I understood it in school. It offers no performance benefit with it there or not there so long as it is functioning properly.
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87 iroc with the usual go fast stuff
heavier than your half ton.
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