Flyseven, there is a performance difference between the OS .70 Surpass II and the ultimate of about .1 HP also the ultimate is shorter by almost 1/2 " also it is a pumped motor so mounting position and flight attitude don't matter on fuel draw. it makes it easier to place fueling valve out of sight also. I use a robart ultra fueler that has 4 taps, carb, tank, pressure feed and tank vent. So it makes for an easy to fuel closed system.