I find that Evolution engines are a mixed bag. Some will run great and others are a continual struggle. When you can buy an OS or TT that are consistant performers why would you want to bother taking a chance on an Evo engine?? Th larger engines are no better. I have both one of the original OS 40 and 46 FX engines and one of the new 46AX versions. The 46AX seems to have a bit smoother idle and a bit more power, not much but its noticable. [8D]