The perfect compression ratio for nitrous is 14:1. For high HP nitrous uses you are going to need a direct port system and better/stronger pistons possibly rods. Also you will need to inject nitrous AND fuel separately from your injectors (wet system). Large doses of nitrous are safe if you prepare for them.
Now water injection and nitrous ... Back in the day I had a 2.3 turbo merkur xr4ti. I ran water injection with that (no intercooler on the xr) and a large shot of nitrous. I accidentally left the water injection turned on WITH use of nitrous. CERTAIN DEATH was the first thing that entered into my mind, but suprizingly it worked nicely together. Now nitrous and water injection without boost? I have NO personal experience so I can't give any advice. Just remember water freezes and EXPANDS. Nitrous gets VERY cold when it goes from liquid to gas.
