2 different dynos,2 very different numbers.why?

same 408 stroker.built by a very rep.builder.his dyno shows 498 hp.518 tq.the rings did not seal and he did not want to stand behind his work.engine biulder #2,torn engine apart and corrected the problem.his dyno shows 433 hp and 467 tq.wow,why the huge difference?thats 60 hp and 50 tq.both are engine dynos.can dynos be fudged to put out bigger #s