"George" wrote:
That said, going down from 4" to a 1 1/2 isn't as good as just slapping my
old noisy wet/dry, with its high vacuum on my Bosch sanders. I'm sure the
fluid dynamics folks can tell you why.

I've noticed the same thing. I've got a BT-3000 saw, which comes with a
blade shroud leading to a 2-1/2" port on the back. My 600 CFM dust
collector's 4" ductwork reduced down to 2-1/2" is almost useless
connected to it. My shop vac does a much better job. I now use the DC
mostly on my 12" planer with a 4" hose. The planer produces vastly more
debris than the table saw, yet the DC gets every drop.

Interestingly enough, I get much better dust collection with the regular
throat plate than I do with a zero-clearance insert. I suspect it had
to do with the wider slot in the regular plate allowing greater airflow.