i remember somebody did a while back...and destroyed their engine...he said he blew a cylinder...
i've read some other reports about the P5 and such...our engine is just not meant to handle NOS in stock form...if you intend on doing this seriously consider getting stronger pistons, and other internals...etc..etc..
I know of at least 4 people that blew their motors due to N2O. I think there is a problem with the N2O puddling behind the butterflies in the intake manifold. Then when they open up all the N2O goes to one cylinder and BOOM! If you really want to do it, go with a wet shot, much more expensive, but much safer.