If I'm reading you correctly and you're asking for the best pulley size, that will be very dependent on the size of the other pulley and the motor speed. The speed of the belt wheel will be the (speed of motor * diameter of motor pulley / diameter of the pulley on the wheel).
Based upon the saw having a 20" wheel diameter, that's about 5' of blade movement per rotation. To get 2000 to 4750 SFPM, that wheel needs to turn at 400 - 950 rpm.
If the motor is 1800 RPM, you need the motor pulley to be 22% of the wheel pulley diameter to get 2000SFPM. A 2" motor pulley to 8" wheel pulley (or 2.5" and 10", or a 3" and 12")would make the wheel turn at about 450 RPM or about 2250 SFPM.
With that 1800 RPM motor, the motor pulley needs to be about 53% of the wheel pulley diameter to get 4750 SFPM. A 3" motor pulley and a 6" wheel pulley (of 4" and 8") would make the wheel turn at about 900 rpm or about 4,500 SFPM.
An 1800 RPM motor typically runs a bit slower than 1800 rpm and the actual diameter would be the diameterwhere the belt rests tightly against the v-notch but this will get you in the ballpark. You can tweak it from there by going one size up or down, depending on what is available.
With the same motor
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