Check out
http://www.hondastyle.com/forums/sho...=&threadid=163
Running 55 shot is safe on stock internals that are in good working condition. You'll want to get a compression test to verify that your cylinders are holding up ok.
One big thing people tend to miss is that if you have any existing problems, nitrous will not fix them. In most cases it'll make them worse. This holds true for any method of forced induction though.
What model & year car do you have (I'm assuming its a Civic since this is the Civic Forum)? Also what kit & what type of kit are you looking at?