If I lower my compression ratio from 11.5 to 11.0 how much horsepower and torque will i lose?

 

Assuming you changed only CR, you're looking at about a 1% loss in thermal efficiency. But when you change CR, you often change things like quench, valve shrouding, piston dome masking, etc, which could also affect HP. It also assumes that you have adjusted the fuel and timing to optimize the CR.

For a 500HP engine, you're probably looking at 5 or 6HP.