Also check LS4.com. If you're worried about keeping DOD leave the heads alone. If not look into L87 intake and head swap they're from the LS7. They are usually good for 45-50 whp but you will have to modify the intake manifold. The LS4 Intake manifold is shorter than the rest of the LS series motors. I also agree with check LS1tech.com. I know I own a 13 LTZ but I am a former owner of a 2006 GXP and a 2007 SS I have a little experience with the LS4.