Just starting build on my second plane, sig 4star 40, looking for your suggestions on best engine. I fly at altitude so I have to go up a bit, my eagle 2 trainer runs an OS 46
thanks in advance

I have the Four Star 40 and have flown it with two different engines: The OS 46 AX and the OS 50 SX. Both did very well, as expected, the 50 had slightly more power.

DS.

Stock requirements are a 46 2 stroke and a 56 4 stroke. I agree the 50SX for 2-stroke power will give you what you want. The Saito 72/82 for 4-stroke power would be just about right

Since you are at a higher altitude you might want to look at the 50 SX (2-stroke) or the FS-70 (4-stroke). This will give you the extra bit of power the altitude will rob from the smaller engines.

Hope this helps

Ken