i've been doing some reading lately on the subject of using cooled EGR at high boost as knock suppression and augmentation of the fuel mixture.
i removed the EGR from my MR2 years ago, but now i'm actually considering putting it back on.
this is one of the items i stumbled upon:
http://www.me.utexas.edu/~sae/Files/Cooled_EGR_and_alternative_fuels_V1.pdfessentially it shows that using cooled EGR at high engine speed/load not only pushed the knock threshold back by ~20%, but also resulted in a decrease of engine brake specific fuel consumption (BSFC) of about 10%.
i read a few days ago that saab engineers were able to run pump gas at 14.7:1 under full boost not only without detonating, but without losing power. seems like an interesting concept.
part of the effect is attributed to the CO->CO2 reaction, which is normally a slower component of combustion but is accelerated by the presence of water vapor in the EGR. leftover unburnt HC's are also given some credit for it.
obviously, EGR is good for part-throttle driving, since introducing spent exhaust into the intake dilutes the incoming air charge (and therefore reduces engine speed) for a given throttle angle, resulting in lower pumping losses.
i think i may give this a try next spring when i take the car out of the garage again. if i can help my BSFC with E85, every little bit counts. i get decent mileage on the highway (~26-27) but this might get me back up around 28-29 and help out with those times when i just can't keep my foot out of it.
the simplest setup i can think of to implement it currently control-wise would be to couple another PWM solenoid to the boost controller, then use that solenoid to feed vacuum to the EGR valve actuator relative to boost. i could even have it dump into the turbo inlet and let the turbo do the mixing.
question is, how the hell to cool it off? a diesel EGR cooler would get eaten pretty quick with SI engine exhaust, both from the heat and the corrosive compounds formed at those temps.