When using Harley Davidson Twin Cam or Evolution heads my basic head work is called a street port. I go into the port and gently massage the port removing all the bumps and sharp edges that are there from the Harley Davidson casting process. Then I compliment the port work with a precise 3-angle valve job. I will re-use your stock valves , guides and springs providing that they are still in good shape & within correct tolerances. This kit will handle cams up to 575 lift cams.