Nitrous on a 318.....how much will it take

In the early 1990's , I raced a 1973 duster. Used 318 lower end, with 340 heads, Edelbroch LD340 intake and (I don't remember which purple camshaft. It ran 13.08 et. At the end of a year , I put a cheater system on it, with the larger jets. I think it was a 250 shot. I hit it right from the start, all 3 gears. It picked up to 11.52 ets. I ran the nitrous for about 5 weeks, then took it back off, since it was the end of the season. No roll bar back then.