It isn`t.
The AX 55 is rated at 1.75 hp at 16000 rpm. How many actually run it at that rpm, it would take a toothpick propeller to get to that rpm.

The fourstrokes are usually rated at much more realistic rpm and opposite to the twostrokes can actually deliver what is claimed.

Ever tried to fill in test data into Pe Reivers prop test hp calculator?? The twostrokes never come close to the claimed hp whereas the fourstrokes actually do


http://mvvs.nl/prop-power-calculator.xls