It has nothing to do with "velocity". It's simply a way to strangle off the air and prevent high engine speeds. A flat plate with a hole the same size as the small end of the cone drilled into it would accomplish the same results- - - - -the cone-shaped restrictor just minimizes the turbulence involved in restricting the airflow. Just replace that part with an insulator like Chevy engines use, and resist the temptation to run at wide open throttle in the lower gears. That restrictor was an attempt to make commercial engines idiot-proof, but the idiots just found more creative ways to blow up engines.

If you insist on using that restrictor, just have a machinist make a phenolic block that duplicates the flange, and transfer the cone into the new part.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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