2 different dynos,2 very different numbers.why?

Different Dyno Manufacturers along with different Software can make big corrected power swings. I had Stuska with Depac until 2009 and went to a Superflow 902 with Win Din software - 1500 HP engines suddenly became 1400. That's why you should dyno at the same location once you have established a baseline for your engine and don't make your purchase decisions off dyno numbers. Check your potential engine builders record at the racetrack and remember an Engine Dyno is only a tool - and should only be taken seriously as a tool to track your progress if you're trying to update or evaluate that the rebuild didn't cost you any power. In the right hands it's a great tool - in the wrong hands it's a tool use to prop up artificial numbers that your racetrack performance will prove...