Exactly. No one ever just slaps headers on and not tune for them....well maybe a dumbass. Headers will lean one out and make it need more fuel. Once you do that, all bets are off as the headers will blow by manifolds in the power department......speakin long tubes of course. I still say for mild street cars, manifolds are forever. They are nice as far as that goes. That said, I am still going to put my headers on my F250 when I swap the Ford 400 in in a few days. Remflex gaskets everywhere and they'll never leak.