If memory serves me right the sig is a tad bit smaller than the greats planes skybolt Which I had and used a 90 supertiger with incowl muff .The plane would do anything I asked of it including straight up torque rolls .MY friend flew his sig Skybolt with a 78 fox wasnt a ball of fire but it flew the plane decent .I would weigh the plane bare and see where you stand.But I think for my munny id go no less than a 90 size 2 stroke or a 100-120 four .Just my 2 cents .