Don,where does your theory of air volume inside the plenum come from. I am still reading up on runner lengths and plenums. I have a very large lid from the tunnel ram pictured above , it made the cut from what I was told ,10 different designs. A turbocharged road race engine with mechanical injection and threaded for NOS. While the lid was in storage something heavy was sitting on top of it and I have to get it popped back out an rewelded in some spots.
I have picked up tidbits of information from here and there, in several books that I have in my library, and on the internet. I participate on another BB that has a great technical discussion on intake manifold design for turbocharged engines. A few engineers have contributed, and continue to contribute on that particular thread. Some have shared interesting computer aided flow dynamic studies on particular intake configurations, including various throttle body mounting distances and angles.
Even so, I will be the first to tell you that I am, by no means, an expert on intake manifold design, although, it is something that has intrigued me for quite some time.
From what I have gathered, an IR intake system where the intake runner inlet is open to the atmosphere (no plenum) tends to provide a broader and flatter torque curve.
A helmholtz intake system (helmholtz resonator), which is an extreme example of using the intake manifold to fine tune the engine, uses plenum, intake tubes and chambers of specific sizes and lengths to provide peak power tuning at a specific rpm range, which tends to be narrow, with the chance that power may be hurt outside of the specific rpm range.
What I've picked up from my reading and studying is that if you want to cancel out pressure pulse tuning within the intake plenum, in essence try to emulate an IR (independent runner) intake system to provide a broader, flatter torque curve, then you want to provide as much intake plenum volume as is practical (space constraint limitations) to help dampen the pressure pulse waves bouncing around inside the plenum. You want the intake runner to feel as if it is breathing into the open atmosphere.
An intake plenum volume of 2.5 to 3 times the engine displacement volume for a V6 engine configuration is a figure that I have seen a few times. Once in a book, and once on the internet. It's not a figure that I've arbitrarily come up with on my own.