[pstrbrc]

Came acrosss this thread for the first time today-waiting for a server to finish doing its updating stuff, so just killing time.
EGR dilution as a way to increase FE at part-throttle on an ignition-type ICE has fascinated me for a long time. Some work I did as an engineering student way back in the late 70's was working towards that. Problem was, we didn't have anything close to the electronic controls that are available today.
OK. Some of the control problem you're going to encounter has to do with the contradiction that your intake will draw through whichever has the least restriction. You experience this when a car with an intake gasket leak runs like cr@$ with the throttle closed, but can run just fine at quarter throttle or more. That's becase when the throttle plate is closed, you are developing high intake vacuum, which can suck a lot of air through a little gascket leak, but when you open the throttle, lowering the vacuum, the amount of air drawn through the gasket leak is much less, AND the metered air flowing past the throttle plate is much greater, and the cpu/metering valve puts in fuel to match this air across the throttle. So, under high vacuum, if you use a monster egr valve, it will be next to impossible to adjust it in such a way that is meaningful. You see, the point of egr is % dilution, and at small throttle openings, that means very little exhaust recirculation, or the car don't run.
Here's a thought:
Ford used variable cam timing on some of the Zetecs (Contour, Cougar, ZX-2) to advance the exhaust timing in such a way that the exhaust stroke wasn't completely scavenged. They were able to use this instead of egr to meet nitrous standards. So how much the intake charge is diluted has much less to do with intake vacuum. The smaller the throttle opening, the smaller the charge that went in on the previous cycle, and so the easier the subsequent exhaust gasses have of getting out during the exhaust cycle, so the lower the total number of exhaust gas molecules left. Now, this isn't exactly linear, but a whole lot more linear than egr.
So, I'm thinking of putting a Zetec /exhaust VCT in my Escort. MegaSquirt the intake, control the VCT solenoid (it's PWM, and I think 12v, but it might be 5v. Have to play with it, 'cause there is limited info on the solenoid.) with an Arduino board if I can't build a pwm circuit in the prototyping section of a v.3 MS board.
But, for those engines that can't alter the exhaust timing, how about an exhaust throttle? You know, they used to call them heat risers? I think GM used them as late as '81 on their V-8s. They used a vacuum dashpot, but you could hook it up to a manual push cable, hook up a pressure gauge to read exhaust pressure, and experiment away.