A YSI is a Renegade blower and is meant for 24 PSI+. I is not very efficient at low boost. He just hasn't turned it up yet due to some low compression on 3 cylinders and oil on the plugs.
He was also at 10.1 AF whan he dynoed it and has leaned it up more now so I'm sure its making North of 800 even at low boost.