Bill and I are in the same club and even though we are friends, we argue engines. I have a couple of Thunder Tiger .46Pros, a couple of Magnum .52XLS (punched out .46's) and 4 OS .46AXs. They are more expensive, but the OS AXs are the nicest running engines I own. They started and ran well right out of the box. No problem with tuning, just pour in the fuel and fly. They are ultra reliable, especially on twins and that's the reason I have 4 of them and not the others.