I don't think going over the best FE point is an issue. The point of this exercise is to cruise efficiently at low power where the engine is so far behind the power curve, there is nowhere for the efficiency to go but up. I'm an engineer. Hypermiling violates the engineer's code of being lazy. So after improving the aerodynamics of the body, big changes have to made by improving the thermodynamics of the engine.
The goal is to modify what I've got. Closing the valves would be no small feat. If the engine was non-interference, the cam shaft could be clutched(?)...but that would still be seriously difficult since it would have to engage like a dog clutch to re-time the valves. I'm going to go with the free flow open valve approach for now and accept the pumping losses.
Remember that the pumping losses are always there. Whether it's six banging or three banging. The question is what the thermal efficiency is that's making up for those losses. On one of the previous threads on this subject, someone mentioned that they had a four banger that became a two banger and it ran like cr@p. The primary issue is not how well it runs, but if it runs like cr@p efficiently. A six banger should be more tolerant of running half dead than a four.
Diverted exhaust would still need a muffler or it would sound like an air compressor, which generally are not that quiet. It wouldn't need to be big since the air volume is much smaller than hot exhaust. It could even be routed back into the main pipe ahead of the muffler.
The dead cylinders would not act as a supercharger. The volume of the dead cylinder is the same as the volume the active cylinders. It would just move air through a more complex path to accomplish the same thing.
If the transmission shifts based on vacuum or throttle position, it would tend to undo some of the advantages of this system. How to lie to the tranny...?
GM, Dodge, and Honda are all doing it now. It's a cool technology, but it involves more than just shutting off injectors. It seems like if you drive them right you could get some impressive mileage, but as soon as you get into the throttle your back to full cylinder operation again. Well, that's true for the Chevy's and Dodge's I've driven. I don't have any experience with the new Honda's.
I will be going on a road trip on 27JUN and will be travelling interstate much of the way... entire tanks of gas at a time I am sure. I can then let yall know if there is a significant diffrerence at least with the honda's when it comes to shutting down from 6 to 3 cyl. Not that this is the point of this thread but I thought I would throw it out there. Knowledge can't hurt...