In response to Larry Mayo's problem, I had the following thoughts:
since the turbine motors Larry refers to are nothing more than vacuum
cleaner motors,  he might want to experiment with a bypass motor as
used in wet-dry vacuums.  These have separate motor cooling fans and
should not be damaged by running with little or no main air intake.

I grant you that they will be harder to adapt to nickelodeon use
because the enclosure will need two more vent holes:  motor intake and
exhaust in addition to main air intake and exhaust.  The manufacturers
warn that the two air streams must be kept separate.  No doubt it will
be harder to muffle the operating noise, but the smaller of these
bypass motors are the same basic dimensions as the air-over motors
Larry is having a problem with, so this might be worth trying.

W. W. Grainger and probably many others sell bypass motors made by
G. S. Electric and/or Lamb Electric, to name just two manufacturers.
I hope this helps, or at least gives Larry a fresh perspective.

Regards,

Joel Hoshaw