the fan is driven right off the pto shaft so the fan is spinning 540 rpm. I think i am going to move the fan farther back in the housing. I looked and had around 1/2 inch of gap between the fan and the back of the housing. on the side of the housing there is probably about 3/8" of gap, but the housing is not perfectly round so it goes from about 1/4 to a little over 3/8. i may add some rivet some rubber to the ends of the paddles so they sort of squeegie the inside of the housing or at least get closer.