EGR?

[Dave Williams]

-> Exhaust is an inert gas as far as an engine is concerned.

 Not quite inert.  It raises charge temps, which promotes better fuel
atomization.  It reduces pumping losses, which returns otherwise-lost
horsepower.  The added charge temp also changes the combustion
characteristics of the intake charge, extending the early phases of
combustion and reducing the later ones.  As a secondary effect,
generation of charge steam as end product is increased, extending the
cylinder prsure curve and returning more "lost" horsepower.

 On fuel-injected GM V8 pickup trucks, disabling the EGR valve will cost
2-3 mpg, right off the top.  The first test a line mechanic does when a
customer brings a vehicle in with a lost-mileage complaint is an EGR
valve test.


-> EGR is
-> used to reduce peak combustion chamber temps which limits the
-> formation of NOx.  In the bad old days (1970's), EGR was added and
-> ignition timing was retarded. This combo made for badly running
-> engines.

 Back in ancient times, yes.  Modern EGR control strategies are more
sophisticated, and the engines aren't laboring under the burden of
early, primitive emission control systems either.  Many "EGR" complaints
of the old days were actually due to secondary faults only peripherally
related to the EGR itself.


-> I would not use EGR in a hot rod unless you are using a fuel injected
-> engine which already has a good EGR setup.

 Adding EGR to a carbureted engine can be difficult as it will drop the
cruise vacuum *and* the air velocity across the venturis, which will
result in a lean cruise mixture.  It can be difficult to calibrate
carburetors to handle this.  However, many carbs run rich at cruise,
such as the primitive Holley four barrels.  You might fangle an O2
feedback to a PWM EGR valve and get a worthwhile return in fuel economy.

==dave.williams at chaos.lrk.ar.us======================================
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