Above: A Solex (Kadron) venturi being removed. They come out from the bottom of the carb. Weber IDF and IDA's come out through the top.
Venturi Performance Differences
In my Complete Kadron Manual, I made the statement:
"There is no direct comparison in performance gains in Weber vs. Kadron venturi sizes, because of the fundamentally different nature of how the two carbs work."
And then proceeded to describe how the plenum Kads and the single bbl per cylinder Webers were different on that technical level. Something vital I should have added was this info -
Venturis with the same inner diameter do not, I say again do not, perform the same on different types of carbs. For a moment this doesn't make sense, if you're judging solely by the inner diameter of the venturi.
Venturis affect intake velocity. Carb barrel diameter, or more precisely, the throttle body, affects volume. Of course, after a certain point, the venturi does become a restriction. But long before you reach that point, what's controlling your engine performance and drivability is the intake velocity caused by the venturi, which creates the vacuum "signal" (actually a suction) to pull fuel through different passages in the carburetor out of the float bowl and dump it into the intake manifold.
Different carbs have different fuel passages triggered by different vacuum signals. This is why the same venturi size on two different types of carbs does not produce the same performance ... right up to the point the venturi becomes a volume restriction.
So, all variables taken into account, the Kad (based on different vacuum signal) gets more power from a given venturi size than a Weber.
FJC
