[Christ]

I think you're looking a little too far into it...

Regardless of engine size (except single cylinder low speed engines) the manifold is constantly under vacuum. When the piston pushes part of the mixture back into the manifold, it's still under vacuum, it's just under slightly less vacuum.

There is still more pressure on the other side of the throttle plate, which keeps positive airflow in the correct direction (into the cylinder, out the exhaust side.)

Even with a 6 cylinder engine, the Atkinson cycle is still effective, as a result of this fact. The only reason for introducing boost is to keep more air/fuel in the cylinder, even though some of it gets pushed back out still. Since boosting engines increases the VE of the engine by adding more air than it could normally induct at the same RPM under vacuum, it also lessens the power loss associated with not having a full cylinder when not under boost.

In other words, the only reason to add boost is to compensate for the Atkinson effect's power loss.

If you add boost, you're increasing the VE of the engine without sacrificing power. If you use Atkinson and Boost (Miller) then you're still getting the FE increase of the Atkinson cycle, while increasing the VE of the engine (less pumping loss).

It's a best of both worlds scenario.

I don't believe the actual Atkinson engine ever intended for the cam to be designed to allow reversion in the intake tract, as this is counter-intuitive for power to be made. As I noted earlier, the real Atkinson design changed only the crankshaft, by adding an ellipsus that would allow the piston to have two effective stroke lengths. A much shorter stroke would be used for intake and compression, then a longer stroke used for combustion and exhaust.

This would yield a result that had less pumping loss than a stroker, but similar torque, with the same fuel use as a smaller displacement engine. VE would also be increased. kinetic energy created per BTU of fuel also increases (energy cannot be created nor destroyed blablabla) due to the longer stroke creating more leverage on the crank during the combustion event.

The idea of the "Atkinson cam" is bunk, essentially. It may increase FE, but it sacrifices power to do it, which is exactly the opposite of the true Atkinson design.