Question, how much horsepower will stock 550 turbo II injectors support????

all depends but i say anything over stock you should look at at minimum bigger secondaries. The stock injectors are almost at their limits when new add a few years some fuel contaminents and your stock injectors are borderline safe for stock. if you are going to stay stock have your injectors cleaned and blueprinted and have fun. regardless of weather you are going to stay stock or mod it larger secondaries can keep things from going boom for some time and large enough and an upgraded compressor and you can have a decently fast car

kinda depends, anything more than 240rwhp, and you'd either be lucky or a good tuner

i dont get the last post