DusterDon is right, you must have an adequate fuel supply. I can't stress this point enough. Fuel, fuel, fuel! No rust clogged pick up screens, no T's off the stock fuel line, no kinked fuel lines and no stock fuel pump. Your stock 5/16 pick-up may be OK for a 100 shot, but run 3/8" line and use an electric pump pushing forward from the tank. Any vapor lock will destroy your pistons, especially since your running cast pistons as they are very unforgiving. If your going to pull the tank anyway to check for rust problems, swap out the pick-up for a 3/8" style. Run a two port regulator with a port dedicated to the carb and nitrous solonoid respectivley. Set your regulator to no less than 6 1/2 psi. This is where an electric in cab fuel pressure gauge is invaluble. When you hit the nitrous, you should not see a pressure drop of more than 1/4 to 1/2 psi. If you do, shut down immediately and re-think your fuel system. Do you need a bigger pump? Do you have fuel line restrictions? Pick-up clogged? Do you need to run a seperate fuel system for your nitrous kit?etc. etc.
Have you ever cut steel with a torch before? Ever notice how the heat just turns the steel cherry red until you hit the lever and add all that extra oxygen and the steel just vaporizes? Thats what happens when a nitrous system leans out.
OK, that being said, I would go no higher than a 100 shot with Auto Zone cast pistons. It would be nice to know what they gapped the rings at, but that would be impossible at this point without a complete teardown. Keith Black says that their hyperutectic cast pistons can withstand a 150+ shot no problem assuming the rings have been gapped per their nitrous/supercharged specifications and everthing else is correct, but I have no personal experience with them in a nitrous application. It would be nice to have opened up the ring gaps on those pistons to the upper end of the stock spec.
Next, file the sharp corners off the ground strap on your spark plugs so they're nice and rounded. This will keep the corners from getting white hot and promoting detonation. Run 93 octane or higher ONLY. Back your timing off 4 degrees and add one degree of timing at a time not to exceed 2 degrees from your original setting. If your times at the strip are not getting faster, leave the timing backed off. Also, check your plugs after every run. If they look lean, find out why. If they have white speckles on them, you have detonation and may already have engine damage. Those speckles are aluminum. This recomendation is for a 100 shot only. You will need to back off more timing for a bigger shot. If you are running a 4150 series Holley, bump up your priamary and secondary jets two sizes unless you are already running really fat. Way better to run fat than lean when running nitrous. Make sure your cooling system is in good condition. A cool motor will help prevent detonation.
Oh yeah, one more thing.
If you have a rev limiter and your finger is on the button when you hit the limiter, you will blow your intake manifold into the next century! OK, I'm embellishing here. With a 250 shot you will, with a 100 shot the results just won't be pretty. Same goes for if you have leaky intake valves. Don't forget that the bottle must be mounted in one position as the "siphon tube" drops down into the corner of the tank. This side up only!
This post is the result of two giant cups of coffee and three years of running a nitrous car at the strip. Hope I helped. Duster318 runs nitrous very succesfully and should be able to add more to what I've written. Good luck and have fun!
