Is this an older plate system? 9psi seems high for the jet maps. Is it a dual spray bar plate (i.e. 1 n20 1 fuel)?

If it was me I'd do some mapping on the plate (orifice sizes in jets mainly) and figure out the lbs/hour at 5.5psi and then research the accepted nitrous to fuel ratios for a "150" shot and go from there. I know that sounds like a lot but engines are expensive and older jet maps were all over the place. I'd have a tough time with the 9 psi but then again it might work fine? I have an older NS EXpress HVH plate that had mapping similar to what you describe. It hit HARD lol. The Monte Smith plate I have seems to come in a little less violent at but maybe it's my imagination.

Can you post the jet maps? I assume this is 150-500?