probably somewhere in the 7.5 or 8:1 range. you will have to mess with timing and stuff like that as well to get it set up right. on all the turbo cars we've built (3) we've never exceeded 8:1. this is low compression if your going n/a but the forced induction will like it. are you going carburated or efi on it? remember that if your going carbureted, draw-thru systems are easier to tune but more dangerous in the event of a backfire (your putting the air/fuel mixture into your supercharger or turbo). also a draw-thru system CANNOT be intercooled, it is MUCH too dangerous. if you go to blow-thru carburation you have to have your carb(s) modified so that they can be pressurized. efi is MUCH easier to run, especially if it is a setup that you can use a laptop on. sometimes the engine management computers will allow you to put in a chip that will hold three or four different tunes on it, that way you can have a mileage or daily driving tune, a race-only tune, or more and then switch between them based on what your doing with the car at the time.
good luck!!!
-tim