750 Brawler vs 650 AVS 2 at the track, right OOTB !

Volumetric Efficiency is a common term, in use for decades. It is actually incorrect, but has never been corr4ected because everybody has got used to it...
What is being measured is the mass [ not volume ] of air ingested by the engine.
As for volume, the volume of air pulled in is the same for any given rpm; what changes is the density of that air.