70% rated manifold pressure at the air density will near give rated RPM from the engine, and rated HP. The stall speed is reduced since the more dense air produces more lift at a given speed. The cruise speed, as the drag goes up by the density, goes down. With the lower stall speed, the take off roll is decreased.
All the things that get worse with high density altitude get better, and vice versa.
I have many hours in an airplane with a horsepower limitation of 180, but engine capability of 215 HP. At normal sea level density altitude, that limited us to 23 inches of manifold pressure, and as we climbed, the throttle was slowly pushed in to maintain 23 inches. Normally, actual full throttle occurred at 7,000 feet. In the winter, the chart of MP adjusted the MP down for colder air temperature, and in hot weather, higher MP was allowed, as the air density was lower. Winter full throttle might not occur until 10,000 or higher.
At 10,000 feet, I cruised at 140 K, TAS, in that Skyhawk.
