As Everett said, the more air you put in the stiffer the ride. You can probably go up as high as 45-50psi and still get a decent ride. It's a fairly heavy car. Watch the back end raise up as you fill them. It's a compromise between ride height and comfort. Experiment and see what's best for you and the car.I think depends upon manf.
AC/Delco - green in color, 90 max
Gabriel Hyjackers, white, 150 max
Monore, yellow?, 90 max.
25 -35 PSI for an enjoyable ride. Might have the MAX Pressure ring on the valve, maybe.