I believe my O.S. 46 AX tached at about 12,500rpms with a 11x7 MA prop, last time I check. Its only got 5 tanks at the most, so it still has that new engine smell. One small question,does anyone know if a pitts muffler does anything to the rpms. The 46 has a pitts muffler ( first one I've owned) and I just didnt know if it is effecting the performance.