Simplifying... Atmospheric pressure is approx 14.7 psi. So 8:1 compression gives 14.7 x 8 = 117.6 psi. However, the inlet valve closes after bdc so you have to reduce that by a factor depending on the cam. For rule of thumb, the expected reading would be approx 90% lower. so 117.6 x 90% = 106 psi. All assuming perfect ring and valve sealing. Pretty close to what you have recorded.