I love 2 strokes (don't own a 4 stroke, in fact), but keep in mind that the OS91 is the dominant engine for good reason under the current SPA rules structure. If you fly a 2 stroke, you will be at a competitive disadvantage in SPA. Since I live several thousand miles from the nearest SPA contest, this is not a concern for me and I would use a ST90 to get the power in a 60 sized 2 stroke. It depends on how competitive you want to be. If winning is your goal, use the 4 stroke. If you simply want to compete with a classic aircraft you enjoy, then a 2 stroke will be fine and you can buy a bunch of extra fuel (cheap fuel, too - no 30% heli mix required) to practice with using the savings from the cheaper engine.


Mark