Originally Posted by ExpensiveTaste
I'm no expert, but I don't think you are correct. Without modifying cam timing, porting the head, using bigger valves, or increasing incoming air pressure, volumetric efficiency will not change...I could be wrong but this is how I understand it.
When viewed as a working system (engine+turbo+induction+exhaust), VE will change. The lower exhaust back pressure (afforded mainly by the big turbine housing) will improve the pumping efficiency of the engine. If the VE of the engine alone will not change of course but that isn't really worth discussing since the engine is just one part of the system.