someone told me that every 30 shots of nos, gives your engine 40,000 on it, is this true?

If you figure there's at least 10 good runs per 10lb bottle that would mean after 9 bottle refills your engine would have 120,000 miles. Since I filled my first set up every two weeks for about 2yrs straight on top of the 60K miles I had when I started using I'd had about million miles on my 1rst engine (which short block was still in perfect shape). Heck my engine now had been through at least 10 refills before it got turbo'd.

I'd say that its nonsense. how much aging it inflicts or doesn't inflict depends on the condition of the engine and how big a shot. An engine could survive a normal lifespan on say a 70hp shot while another may die on its first and only run if its tired or cant handle a shot that big.

What He--^^^ said.

so If I get a 50shot, then I'll be all set and not putting miles on my engine?

Not putting miles on your engine? I think you mean wear. I have a friend with a 94 Integra GSR. The B18C is a damn strong motor. With 60,000 miles on the motor he cook all 8 exhaust valves. It looked like they had little bites taken out of them. But he was always on the bottle. He had it for about 2 months and would go through at least a 10lb. bottle a week. HE ran high speed runs with it, something that the guys at NOS dont recommend. You'll be fine with the 50 shot. Do a baseline leakdown or compression test. then just do them once a month.