Some good advice on this post. As a previous nitrous user, you can't just plop 300hp kit on an N/A application and expect to get the same results of a nitrous set up. Your rings may be too tight. You may blow through your converter and if you have a lot of gear from N/A passes, you may run out of gear. For a smaller 100-150 shot, generally, you can get away with running it on top of an N/A set up motor.

Either way, with that much nitrous, YOU MUST back timing down considerably, run at good fuel (you didn't say what your current combo compression ratio is) and colder plugs.

Good luck and post your new times!