Hello; I have a 4 star 60 with an OS 90 in it, it's the earlier OS 90 with the pushrods in the back. I think you'll find that you need quite a heavy engine to balance your 4 star. This is one reason to consider the OS 91 or Magnum91 over the lighter Saito. I put a Saito 100 in my 4 star 60 and found I needed a pound of weight to bring the c of g into line, so I looked aoround for the heaviest 90 size engine I could find.

I think you should look at Magnum, save yourself $100. My engine choice will be the lighter Saito's, because of the design. I have OS' entire surpass line, but I fly Saito. I have a surpass 91 I bought new but I have taken it off 4 planes now and replaced it with saito. If I need a heavy engine, I'll use OS. I find that more and more flyers are unhappy with the larger OS four strokes. I know that lots of people like them, but no one here.