Dont know if this is in the right place but this is why I dont mess with NOS.
http://www.youtube.com/watch?v=gUvkX3uH6Fc
http://www.youtube.com/watch?v=gUvkX3uH6Fc
The problem there is he activated the nitrous too soon. The Cobra motors don't flow enough air at low engine speeds to get all that nitrous to the chamber, thus a backfire through the intake. RPM activation is the only way to go with a mod motor, or that will happen. It's not the nitrous' fault. It's user error.
the great thing about the spary is that you dont have to kill supercharger to make great power. after 15lbs that eaton is working. you can always go with a big whipple, but the spary is easy and effective. but it is all in the tune.