Originally Posted by Kurfürst

Top speeds at SL and rated altitude are coded (ie. set by developer manually. Currently its 470 at SL (which is double wrong as I suspect it should be attainable only with the 1175 PS rating instead of the actual 1045 PS rating), and 560 at 4500 meter for the Emil). I guess the engine works out the rest of the graph from these figures (its pretty obvious between SL and FTH, the above probably follows the same rules for all planes, taking into account stall speed, which is also manually set.