I tried searching but no luck, so I'll ask :D The 383 I have I just found out uses a cast 400 crank. Whats the safe RPM and HP limit with these things? Its running 6000rpm shifts and about 400hp right now, and I was thinking of upping the cam and adding some NOS [like a 100hp shot]

500hp and 6000rpm it ought to last for a long time.

I have been doing excatly what your thinking of doing. I am running 11.40's and the 100 shot doesn't even tickle the engine. Make sure you fuel delivery system is up to the challenge. I use a 130gph Holley mechanical fuel pump with a regulator. I like to run 6.8 psi of fuel pressure. I check the plugs after each run to make sure I am set up correctly. You may also want to drop your timing down 4 degrees. In cooler weather (80 degs. or below)a bottle heater will come in handy to keep your nitrous psi around 950. The engine has been getting faster with no signs of any damage.

I know of one 406 running a stock cast crank that gets shifted at 8000rpm and has been holding up for years. The engine is in a 1960 Impala that runs 10's. The car twists so bad out of the hole the whole underside of the car is visable, big time torque.

Just have the crank checked out....damage is cumulative...I wouldn't take one pass 6k and 150 shot too many times however