I used to have one of the OS .70s that I often used in 40 size planes. They had gobs of extra power. I regret I sold it because I never cared for the newer OS .70s. When you compare a YS then you may as well compare a .70 to a .70 because the YS is that strong compared to other four strokes. Saitos are a great engine but I like my four strokes to have a pump and I do tend to lean towards the YS engines. That is one way to forget where you install the fuel tank.