How much power output should i get if i put on 9psi ATI blower which i think is intercooled on stock 1991 L98 automatic, Camaro Z28?

I would say to post your question on the power adder board you will get a much better responce from over there. Needless to say it would be quite a bit of power.

I'm not positive, but I think when running boost, you want your compression to be around 8:1 , not sure what the stock is on your motor.

I just put an ATI ProCharger on my 89 Formula 350. Depending which unit you buy will determine the power output. They told me on a stock L98 engine that the P1SC unit will develop about 110 horsepower at 9 psi boost. The D1SC will develop around 140 hp at 9 psi boost. They also told me that on the stock 9.3 : 1 bottom end not to exceed 12 psi with an intercooler. I'm running 9 psi on my car. Say bye-bye to any traction under 35 mph