541" X 5,622 RPM at 100% VE is 110 CFM?
But that assumes continuous flow though each successive passage (booster venturi, manifold runner, intake port) which never happens. The port has a duty cycle (not on-off, but high-low) roughly related (but not linear) to the cam event. The CFM calculation assumes maximum vacuum @ WOT of 29.92" Hg.
The frequency of vacuum pulsing remains constant with RPM, but the amplitude (pressure cycling) is lower in the manifold, and even lower at the booster due to plenum volume.
Large displacement at moderate RPM makes it worse (as opposed to a smaller engine at higher RPM).
Where to go from here?
Obviously, a big plenum box extending sideways over the valve covers helps with the height problem.
Tuned length runners must be really long to work at moderate speed, and not really needed with big inches, and any port extension inside the manifold deducts volume from the plenum.
Anyone got ideas?
I used 93% efficiency to suggest a typical moderate build. At 100% it slides up to 116 cfm per runner. As a whole, the math says 936 cfm for a 541 at 100%. Then, you get into real world restrictions, carb sizing bumps, and such.
Breaking it down into a single cylinder is a bit easier because heads are rated per runner, not as an engine set.
It would be nice to have a variable runner EFI intake but that's a completely different can of worms. While I might like it very few would want to put "that ugly thing" on their engines and Mopar guys are notoriously cheap.
I would think that frequency of vacuum pulsing would remain proportional to RPM instead of being a constant value. Amplitude would certainly be lower at higher rpm due to changes in density.
Plenum volume is a bit of a mess on a carbed engine since fuel puddling can occur at low air speeds. Having a wide carbed plenum can also play havoc on fueling since liquid (no matter how small the droplet) has far more density, and therefore inertia, than air. Fuel can fall down go boom at low air speeds and get splattered against a wall at high air speeds.
Throttle body injected engines need a bit of open plenum below the injectors. Divided dual plane intakes often struggle with those systems.
Port injected engines are more tolerant of plenum changes because the flow is dry.
