Need help to find a pulley diameter.

['83 chevy]

I'm reworking our back up air compressor, and I'm having a hell of a time figuring out what size pulley I need on the motor. The Pump has a 13" flywheel, and needs to turn 1200 RPM, the motor is 1720 RPM. I can't for the life of me figure out what size the pulley on the motor should be. We had it direct drive before, but the 3 HP capacitor start motor did a number on the pump, so I don't want to wreck it again after just rebuilding it.
Any help?

 

[_BEN_]

Someone confirm this.

1200/1720= 0.69767

0.69767*13"= about 9" (9.069)

mcmaster may have the 9" pulley you need.

 

['83 chevy]

ok thats what I came out with. I did 70%(1700/1200) *13 and came out with 9.1 so I was right.

 

[_BEN_]

A 9.1" will spin the pump slightly faster. A neglegible amount probably.

 

['83 chevy]

I'll just get a 9" pulley,