the comparison plots i have seen basically show a vertical shift of the power curve at whatever rpm the nitrous activates.
so, imagine the normal curve before the nitrous activates, and then a sudden and nearly-vertical line when the nitrous hits, say 3500 rpm, that shifts the power curve upward approximately equivalent to whatever horsepower the nitrous shot was (i.e. 100hp, etc...), and then basically parallels the no-nitrous curve at the top end. really "fattens-up" the mid-range by changing the shape of the power curve from the usual 'sigmoidal' curve typical of turbocharged motors, to one resembling a 'logarithmic' curve.
an exaggerated example at this link (blue line is logarithmic; red is sigmoidal):
http://www.cryst.bbk.ac.uk/pps97/course/section12/hbcv1.gif
clear as mud? lol
craig