Street or track??
Everything depends on your suspension and surface you are running on. You want to run as high a pressure you can while still getting the car to hook.
I would start around 16-18psi and go down from there. You should be fine all the way down to 10-12psi.
Maybe some of the DR guys who race at Milan on Fridays can chime in......pretty sure they switched from MT's to Hoosiers this year.
--Joe