I'm no expert, but I would have to say that the ZZ design intake is completely from as from a air flow respect. To many sharp edges, no radius on the ports. I've spent countless hours on a flow bench trying to understand air flow. I've been working on one for my truck, will try to post pictures.
Another thing I noticed is the length of the spray bar that they use in some of there manifolds, way to long, or should feed it from both ends. By feeding it from one end ony the pressure drop is major when the solenoid is activated. We had issues on a pro-mod car with a set of spray bars in the manifold plenum and they were only 15" long, let alone 30" like a cummins.
scot