I have a UCD with a Saito 100 swinging an APC 16x4W prop at 9800rpm. My friend has a YS91 on his and swinging an APC 15x4W prop at 10300rpm. We are both using 20/20 fuel. Pretty much the same power, they both give around 16~17lbs of thrust which is more than 2 to 1 power to weight ratio. The YS maybe a tad heavier? don't know. Mine weights at 7.6lbs....