Ok....I see from your other post that this is no street car.
You are going to need an electric fuel pump dedicated to run the NOs fuel only,run 114 octane gas thru the NOs solenoid,if you don't want to run the engine off 114 then you will need a seperate fuel cell(that's what I did).I highly recommend a low fuel pressure safety shut off switch.Also if I were going to run a 400HP NOs shot,I would do it with a fogger system not a plate system,that way you can tune each cylinder seperately to make up for any lean/rich conditions.(Some intake manifolds will "starve" certain cylinders a little due to their design)cyl. #8 was mine.
I ran 250 HP shot on my Chally and it went from 13.22 to 11.83 so you can imagine what 400 will do.I have a video of the run,just have to figure out how to post it on the internet.
You will have to retard the timing as also mentioned.If you go lean,you will burn something,first thing is the spark plug tip, then a piston
so start out rich.
I recommend you not start out at 400HP,more like 150 and then work your way up.
