Mechanism of Intake Pumping Losses

I'm a mechanic and I'm debating the exact mechanism of the so called "pumping losses" or "pumping work" of conventionally throttled 4 stroke spark ignition engines.



We know that EGR is employed to reduce intake pumping losses and actually increases engine efficiency for slightly better fuel economy, but we disagree about how.



My claim is that higher intake manifold pressures actually transfer energy to the piston on the intake stroke.



My feeling is that if there is an extremely high throttle restriction, and lets say, 30"hg of intake manifold pressure, the engine will lose more energy on the intake stroke as it *drags* the pistons down the cylinders.



I'm basing it on the surface area of the pistons, and the engine speed. I feel the inefficiency created by throttling comes from discarding the energy in the atmospheric air.



Can't have something for nothing. My colleagues seem to think the energy is lost across the throttle.



I can understand a reduction in volumetric efficiency due to the throttle, but not combustion efficiency.



What is the truth, really? Where is the energy wasted on an engine without EGR? Is it related directly to MAP, or to the throttle angle?



Dying to know.



Thanks,