Originally Posted by polyspheric
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?


This is a really good post. Some thing like the Offenhauser Small Block Chevy Ram Intake Manifold.