head swap
 

I've read about PI head swaps a good amount of times over time of being on this forum but never really got the full understanding of whether it's worth it. These are about the only things I've read that I get full clarity on and please correct me if i'm wrong, you will only yield ab 11hp from a PI head swap and P&P Non PI heads flow better. I see the threads usually turn into an argument about it only being 11hp gain then how it also raises the compression. What I don't understand is people I know who do the swap on mustangs and see better gains. Are they swapping more than just heads? Is the bigger gain from doing the intake as well? To see decent gains would it consist of changing the heads,intake,cam, rockers and springs? I am not necessarily looking to do it I just looking for the knowledge although it has crossed my mind a few times...
Thanks