I do not know the particulars on your Corsair (how much it weighs), but I do know that if "THEY" recommend a 1.20 4 stroke and you are contemplating the Saito 3 cyl .90, then you are looking at giving your Corsair about 1/2 the recommended power. As mentioned above, multi cylinder 4 strokes have less power, while having more weight, than comparable displacement single cyl. 4 strokes. In other words, your 3 cyl. .90 will have less power than the Saito .91, yet the .3 cyl. will weigh more. If you anticipate that the final aircraft weight will be under 9 lbs, then it just MAY work, but it kinda looks marginal.