[Gary H]

First, the factory ACTUAL compression ratio would be less than advertised 10.5 you mentioned. Generally, the actual CR is around .5 less than advertised. When you pull your current #13 heads you can check the piston to deck height, and the type piston that was used and then calculate what the compression ratio would be using the new #12 heads. To be accurate get the heads combustion chamber cc'd. If you still need to change pistons to lower the compression ratio consider the dished Icon forged pistons. One advantage for these is that you will have a better 1/16" 1/16" 3/16" ring pack than came on your current pistons, which is likely 5/64" 5/64" 3/16". There's some increase in HP in the thinner rings alone. Also, the roller cam should make an additional increase in horsepower if spec'd right.