Are you talking about a cone stack pulley arrangement?
Like you see on the J head Bridgeports (among others)?
If so, 14 speeds means you'll need a stack of pulleys 14 tall...
Another option is to use a 2 stage setup like you see on some mill-drills.
That would lower the number of pulleys and help with the slower speeds.
Anyway, on to your question, to get the speed ratio, you simply look at the diameter ratio of the pulleys. For most machining purposes you can use the outside diameter of the pulley, but this is an approximation.
So as an example, let's see what you need for your first speed of 80 RPM.
(also realize that this is a somewhat unrealistic speed reduction for a single stage belt - that's why b'ports etc have a back gear)
Your input is 1750 and your desired output is 80
look at the ratio of the two and you get 1750/80 or 21.875 (just divide)
That means you need a diameter ratio of 21.875 on your pulleys.
If you are slowing down the little pulley goes on the drive side, big pulley on the driven side.
So, if you use a 1" diameter pulley on the motor side (for easy math, can't actually get that with a 4L belt), you'd need a honkin' 21.875" diameter pulley on the spindle. A 2" drive pulley would need a 43.75" driven...
That'd get ya 80 rpm.
Hope that helps,