Rotary gap motors



I received the motor for my rotary gap yesterday.  It is rated at 10,000 rpm
at 115 v ac or dc.  I tested it with my variac and tried to measure the speed
using a tachometer that I built from a kit for measuring the speed of
airplane props.  It seems to be running at 15,000 rpm with no load.  Does
that sound reasonable?  I know I need to control it to keep it the rpm
somewhere between 4000 and 5000.

When I get the gap finished, I want to build a wooden box to sit over the top
of it.  I was planning to mount a fan on one end and drill a 2 or 3" vent
hole in the other end - to provide some cooling.  Is a 100cfm fan large

Thanks,  Ed Sonderman