it all depends on how you set it up centrifugal supercharger
That's the key: blower speed can't be changed without replacing some part of the drive system: one or both pulleys, and possibly a belt (if you run out of adjustment).
Not all ratios are possible with pulley combinations you can buy, or will fit into your bracket set.
A much more complicated method, but that allows easier ratio changes afterward, is a jackshaft with a secondary ratio built into its pulleys. This allows the blower and crank pulleys to stay in place (much less work stripping the engine); you just substitute different diameters on the jackshaft.
Example:
Engine 6"
Blower 3"
Ratio 2:1
If a J/S is used, it can have a 4" at the engine end and anything from a 8" down to a 2" at the blower end. The pulley diameters can be smaller or larger than the originals because they don't interfere with anything.
Math: crank ÷ J/S-1 × J/S-2 ÷ blower = ratio
Example:
6 ÷ 4 × 8 ÷ 3 = 4:1
6 ÷ 8 × 4 ÷ 3 = 1:1
