My first choice is the OS 70 four stroke but after trying the SK engines from Kangke any time I need A two stroke the SK is my go to engines. Can't say enough good things about them. Best thing I have found in the under A hundred bucks engines. I have the SK 90 in my 60 size aeromaster after yanking out the 68 MDS and it turned it into A complete new plane. They come with A good muffler but I have gone to the PITTS type.