My short story:
Did a dyno on my stock rb25det S1....got only 180bhp atrw.....from the graph A/F was very very lean....damn dangerous & freaked out.
Suspected it was a faulty fuel pump, changed to walbro 255l (& FPR) then dynoed again with 0.8 boost got 255bhp atrw with very safe ie rich A/F ratio.
Hope that helps.