the rods don't lower the compression, pistions and the heads have cc values, the lower cc values on each will give you a higher comp ratio, as there is less area for the " bang " to go. I think techinspector1 might be able to give you the exzact cc of the parts you need to make 8:1. he has a nice write up on how to figure them out also. I'm sketchy at figuring them out.