"leaning" with EGR or air?

[GasSavers_Erik]

With all of the talk about "lean burn", a/f ratios, keeping the throttle open to increase dynamic compression and reduce pumping losses... what are the advantages and disadvantages to using extra exhaust gas vs. extra air to dilute/lean the mixture.

Leaning mixes (with air) means they will burn hotter and can preignite or misfire.

What about simply diluting with high EGR? It burns cooler and since exhaust gas is inert (non reactive) you really wouldn't be changing the a/f ratio. Disadvantage- I could see how that non-homogeneous EGR/AF mixtures may be hard to fire off with a single spark plug.

How about a throttleless gasoline engine that varies speed and power output by increasing or decreasing the proportion of exhaust gasses that the engine is breathing? Compression would always be at max and there would be no vacuum for the pistons to pull against during the intake stroke.

The reason why I bring this up is because I have been running my 87 civic with and without my EGR vacuum line hooked up and I seem to be getting better mpg with EGR.

Maybe even more EGR could be better... anyone ever try increasing EGR?