might be confusing terms... For best volumetric efficiency, you need 100% wide open throttle. Its a ratio of how much air is going into your engine, vs theoritical max amount based on displacement. (a 5.7l engine sucking in 5.7l of air is 100% volumetric efficient, which is essentially impossible without a turbo or some really clever tricks of the intake, which are only good at very specific RPM's) A throttle plate destroys volumetric efficiency, that is its purpose, to throttle the engine.
In terms of VE, the absolute best engine is one that runs at 100% output all the time, and doesn't even have a throttle plate in the way to slow down the air. That is the reason VE isn't generally talked about in terms of economy, because you generally don't have the luxury of sizing an engine perfectly to the load. In most real world applications you need a throttle plate.
The OP's engine is maybe around 30% VE at partial throttle steady state 3200 rpm, and maybe 85% VE at WOT max rpms.
