Hi Lyle Glad you got my point. A properly trained voice trying to sing rock sounds naff unless he throws the training out of the window. The attributes and aptitudes of rock/blues singing tend to come naturally and can not really be taught. They also go against a lot of classical teachings and techniques.
Anyways back to this yell. I try and keep these down to a controlled level a la Plant/Daltrey. To do otherwise will kill your voicebox. It is all down to practice, technique and knowing what you are comfortably capable of. If it strains hurts or burns do not do it. Listen to Daltrey in Wont get fooled, His yell after the keyboard solo although loud is controlled. He practices and perfects techniques to do that believe me. We cover that song and it took ages for me to perform that bit. I gradually worked my way up to it.

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055