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Just my thoughts;
EGR was originally designed to reduce peak combustion chamber temperatures(high NOX emissions), which should reduce power since its a direct function of the difference in temperatures between the intake charge at the instant before combustion occurs and the peak pressure die to combustion of the same charge. In most cases when you disconnected EGR you created heavy spark knock and had to reduce the timing to compensate.
My VX has EGR and I wont disconnect it, because its illegal (you could be fined $2500 as an individual) and I believe it is an integral part of the lean burn system. Now I could be wrong (wouldn't be the first time).
Air injection was rendered unnecessary when fuel shutoff was utilized with fuel injection, and possible some of the more sophisticated later carburetion setups at the end of the carb era. Without high vacuum fuel delivery there was no necessity in adding air to the unburned fuel in the exhaust. Fuel injection fuel shutoff solved the problem.
I would imagine EGR could also be eliminated by simply working with back pressure and valve, size and valve timing to keep a residual amount of exhaust gas in the combustion chamber. In my opinion there is always a small amount that would remain anyway, without forced induction or other means of purging the last remnants. No way the piston can force all the exhaust gas out of the cylinder, due to non displacement combustion chamber volume.
In 1975 when Nissan introduced fuel injection the system was good enough (in the time period) to allow them to eliminate the air injection, EGR, and cat converter. I always like that year but the fuel injection was fairly primitive compared to modern systems.
The nice thing about no EGR was the fact that the inside of the intake manifold didn't have the tar like residue due to the mixing of PCV vapors with exhaust gases. Later systems had EGR.
The same year California cars had cats and EGR.
regards
gary
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