I don't know the details of this particular VFD, but is the number of poles of the motor just a parameter to set up in the VFD? Then of course, the motor windings will be connected Delta or Star according to your real world choice.
True, the 8 pole setup will develop full horsepower at a lower rpm (perhaps 900rpm?). However, you don't want to "lie" to the inverter setup about the number of poles (by saying it is a 4 pole hookup when it is actually 8) , or it could allow too much current to flow and burn out the motor.
So it depends on what speed range you find really the most useful. It is conceivable to use the 8 pole setup and run the motor frequency up to 240hz to get 3600 rpm. This way, you will get full motor hp at 900 rpm, and it will stay at that hp up to the maximum. Whether this high of a frequency would damage your motor insulation is something to consider, perhaps.
The motor should not normally have a big imbalance problem up to 3600 rpm. If it does, I have had good success with disassembling the motor and balancing the rotor, just by setting up parallel knife edges, and letting the heavy side roll down. Just remove a little bit of metal from the aluminum bar fins of the rotor to improve the balance.
Be cautious of the quality of the fan if you run it up to 3600. Make sure the fan is in excellent condition, and keep it shrouded.
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