In think NOS is not so good for the engine.Because you have a 4.2 l Audi V8 they are very dangerous to blow.
You can also install Bi-Turbo with it you can have nearly 600 Hp but it is also dangerous for the engine I think.Why you would have more HP?

Wer Audi V8 fährt braucht sich um seine Freizeit keine Sorgen machen. xD XD XD