Badangle, There are many more moving parts so there are frictional losses, also a two stroke fires every rotation. Vibration levels and torque impulses are very high. Each cylinder in a 4 stroke fires every other rotation but is scavenged more completely that a two stroke. Having 7 cylinders fire every two rotations have lesser torque fluctuations. An advantage of these radials also is high torque developed at lower rpm so a big efficient prop can be used. -Tom