How much boost do I need?

If you are making 275 hp at the wheels i would say low boost somewhere around 5 or 6 psi but that is a guess with as little info as you provided

Sorry - I disposed of a lot of my Stude reference material when we moved to Florida.

But we had one - the kewl thing about the '57-'58 unit is the variable-ratio pulley which the later '63-'64 units didn't have.........it provides appropriate boost for the speed at which the engine is operating - but with the electric kick-down feature, can go to "full boost" ratio when the pedal is floored.

Seems to me that at most speeds, the unit puts-out about 4 to 5 pounds boost - and maxes-out at around 6 to 7. It's sort of equivalent to raising the compression ratio from the unboosted 7.5 to about 12 to 1 ........ requiring some pretty good gas. The '64-'64 R-2 engine similarly had fairly low boost . . . . and I think the rare R-3 maxed-out around 9 lbs.

If you need help, there are lots of experts in the Studebaker Drivers Club and their website forum undoubtedly discusses this. The "guru" of blown Studes is Jon Myer . . . . Myer's Studebaker Service near Zanesville, Ohio. The do all Stude work, but are a leading source of parts & service on the superchargers - they rebuilt ours and it's sweet !

ADDED:

. as I recall, there is a little flapper air valve in the pressure bonnet that is to OPEN when engine is off.......it is NOT a pop-off to limit max boost, but to equalize pressures when engine is off ... the '57-'58 charger set-up makes a little boost even at idle, sufficient to close the flapper.

. the number 1 thing to remember about those units is to keep the lubricant reservoir full . . . . think they take Type A trans fluid . . . the reservoir doesn't hold much (it was back in the day of 1000 mile service) and if it runs low the ball bearings will be toast in short order.

this depends on the power required to run the supercharger. I would guess around 350, but I need to know what type of supercharger it is.