I have a g37s and I have about 105k miles on my engine and i’ve been thinking about getting the stillen supercharger kit and my car would probably be at 120k miles by the time I get the kit would my engine blow up? Is 120k miles to high for the kit? what would I have to do to my engine so it would be fine with the boost?

I would send an oil sample from two oil changes to Blackstone Labs before adding forced induction. If it comes back with high steel and/or aluminum, that indicates a lot of wear on the crank and rings, or cylinders respectively. If that's the case, back away from forced induction as your engine is worn. If not, go to town and get a good tune.

Oil analysis and compression test, if all checks out do it

Thanks for the suggestions guys 👌🏽