I see your point, but in my limited experience with boosted engines the manifold pressure seems to be more or less constant but dependent upon RPM. I don't know but I'm going to guess that the cylinder fill vacuum is greater than typical boost pressures seen on gasoline engines.
Not entirely sure what you mean. I'm just saying ithe boost, whatever it is, on the backside of the valve is filling the cylinder so there isn't going to be a differential across that valve equal to boost pressure by the time that valve is closing.
(It's not just 15psi boost behind valve and zero psi in the cylinder as the cylinder is being filled by that 15psi, for example)
