The CTS-V should have 243 heads already. You can just take them off and work them out instad of buying another set of the same heads. Put a cam in it and you should be fine. Just a healthy cam will get you 390-400 RWHP. Port the heads and you can be in the 420-440 range. Look at some headers and better cat back. Anything above that you are looking in a fast 90/90 intake, AFR or Trick Flow heads etc.