How much nitrous for a stock piston?

I dont think 150hp is a problem. I've run 175 on a stock 318 and a stock 383 with no issues, and no dedicatef fuel system. It's not the safest, but it worked. If you are serious about running nitrous and plan to in the future, invest in a progressive controller. It will help you here, and be expandable later. You dont need to pull a lot of timing out and I don't think there's any need to mess with jetting. I pull fuel pressure out normally. The 175 kit I had a steady 4.5psi on it because 6psi ran it way rich like Bob mentioned. If the car feels lazy, that's what the bottle's for. I used to hit it in 2nd with a stick but with an auto, right off the line.