That's a very good question E-Dave and one I've wondered about too.
ORIGINAL: jaka
Adding nitro (5-15%) to most sport engines will raise the hp/torque curve at all rpm! That simple.
Jan, I don't know whether or not it is that simple. Have you plotted this out in controlled testing?
It should be easy to test: run three or four different loading props on the same engine with low or no nitro, tach the peak, use the prop-power.xls spreadsheet to calculate the HP ratings for each prop, then repeat after "tipping the can". Then plot the numbers using Excel - you will end up with two power curves to compare.