Work = Force * distance
Force = Pressure * Area
Work = Pressure * Area * distance
Swept volume = Area * distance
Work = Pressure * Swept volume
italia,
the different ratios of change of pressure and density are explained by the temperature lapse rate. That's what you see running it through the gas law as I did above. The pressure drops more than the density as you climb, but that's due to the temperature dropping as well - lapse rate, or the RT/V term with R and V kept constant. Compress it to the same MAP again and the temperature comes right back up, meaning trying to find the MAP difference in the difference between temperature and density ratios is chasing a red herring. In the manifold, conditions will be the same in the end once MAP is equal.
(Don't forget the disclaimer, not doing a lot of thinking here
)
Regarding the quote, there's no need to consider the prop for it to make sense. What the text is saying is that as RPM increases, the RPM of the supercharger (geared to the crankshaft) increases as well and delivers a higher MAP. You initially left out the bit about it applying to a supercharged engine.