I believe the #8 was pre existing, a nitrous backfire wouod break a piston if anything not melt a piston. Id rather not say on the tune because its not his fault, he just did the motor tune. I just took 4 degrees of timing out for the nitrous tune and dialed it in with the fuel jet.
Just some advise so you don't blow your new motor you can NOT tune these cars solely off of the fuel jet like an older car, its very fustrating seeing people doing this over and over and damaging their motors. Also 4* on a 200 shot with even race gas is just asking for trouble. Almost anything you have ever learned or have done with nitrous in the past just throw out the window and start fresh when tuning these cars, their needs are much different.
Like JPC said, read the plugs properly and they will tell the story. Unfortunately reading plugs is a lost art and many don't know how to read plugs anymore.
Good luck with the new build, looking forward to seeing the track times.