You are right about the general rule of thumb being plenum volume should roughly equal engine displacement, on a normally aspirated racing motor. This prevents the engine from bogging during closed to wide open throttle....
OK, then let me ask about a single 4bbl. engine? I have in front of me a MP W2.
In order to figure out plenum size it is HxWxD correct? And then X's 2 for the suggested engine size that it should feed?
And somewhat less for a street/strip engine, less for a street engine, etc...
Runner length is left out because it is seen as an extension of the intake port?