[Daox]

Originally Posted by pstrbrc

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.

We're just going to have to see how far down I can dial the larger EGR valve. I might not run into the problem. If nothing else, I could use a smaller valve in addition to the larger one.

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.

I can't imagine that placing a restriction in the exhaust is a good way of increasing efficiency.