Originally Posted by
Fitero
Where I can surpass the original design is by making the ports with better flow characteristics. Their method of joining two bells in the center has left a sharp ridge, which for a venturi is anathema and results in disruption of laminar air flow.
So again, a simple measurement of the bell diameters, port length and centre I.D. is all that is needed to make the copy.
If that can't be obtained, then you are right in that I would have to rely on available port calculations to get a brute proximity.