J. Phil Thien's Projects

Beware; One consequence of increasing the performance of an undersized impeller would be the increase in power requirement may exceed the ability of an over-rated motor causing it to overheat and fail.  My shop vac fan draws cooling air thru the motor as well as thru the filter and maintaining this flow would be a critical factor.

Good practice would be to monitor both motor temperature and motor amps when improving the impeller. 

Amp draw is proportional to the work. Generally restricting the output raises amp draw as the fan does more work to create a higher discharge static pressure. And, restricting the input lowers the amp draw as the intake pressure drops.