On my NA, I did the headers with the plenum off, no need to remove steering knuckle because they slide through the top fine, at least on the drivers side. I still took off my oil tree and went through the bottom on the other side. As far as HP gain, it feels more responsive and the torque curve changed. I wouldn't say it was a waste as I replaced the valve covers and some other things at the same time, plus the headers were free. I wouldn't pay much for a set if i was looking though. Not worth it if they are spendy.