Thanks for the post!

It really depends on:
1. What the RPM range of the new Pump is & diameter of the Flywheel.
2. What the specs on the Motor are.

If you can take a photo and upload the specs on the motor label or just type them out here (RPM's, Amps, Frame size [FR] that'll certainly help.

There is an easy formula you can use to find out what size Pulley you need. You'll just input the diameter of the Flywheel, RPM of the Pump, RPM of the Motor, and it gives you the target size for the Pulley you'll need to achieve the correct RPM's on the pump.

If you reply with this info I can easily confirm the Pulley size you'll need. You want to be accurate as you don't want the pump to spin too fast (you'll wear it out) or too slow (lower CFM output).
Thanks!
- MTR

Thanks Chip.

What you'll need is an 3.8" diameter Pulley. I don't think you should go larger as it'll spin the pump faster, but it'll wear it out quicker as well.

So to be safe, I'd install a Pulley no smaller than 3.5" but no larger than 3.8" or 4" (MAX).

Hope this helps!
- MTR