A 17cc engine is fairly small for a gasser. I figure it like this-

Gas vs nitro- A gas engine is about 2/3 the power of a comparable sized nitro. So a 17cc or 1.03" engine is the equivalent of a .70 nitro. Using this calculation will tell you what size model, prop, and more importantly what weight model you can fly with it. But you also must consider that a gas engine is (usually) much heavier..