Thanks Gerry.
I've heard the "six sizes" rule of thumb before. Probably a good starting point.
Not sure, might leave it in.
I always thought of the power valve in the secondary of a vac. sec. Holley a little differently than has been described, but am open to the idea of re-thinking it. Especially from folks who have possibly experimented and tested far more than I.
Entertaining theory only perhaps...
But if you were rolling along at a steady throttle state, say 3/4 for example. And the venturi vacuum combined with the secondary diaphragm spring were enough to allow the secondary to be open to some degree, it could be running on the primary and secondary main jet circuits but have enough vacuum signal for the power valves to be closed. Roll in more throttle opening, thus a vacuum drop and the power valves may open and provide enrichment on demand.
This built on a foundational ideology that a mechanical secondary attached to my foot may often result at times in a throttle opening that is a mismatch for engine demand, while a properly setup vacuum secondary operates more on engine demand.
This also combines with the recognition that for example- an engine dyno load doesn't necessarily accurately represent the loads and demands of real-world application.
Now i have to go back and evaluate- Is the power valve signal tapped form the same location for both pairs of venturi?
Forgive me, I have been living in a ECU controlled EFI world for too long now... This may be little more than throw-back cranial exercises.
