ORIGINAL: Avaiojet
I strongly believe the 1.20 just isn't enough engine for a bi-plane at 80"
I suppose it depends on the biplane. I do WWI and my next model will be a 85" biplane (Albatros CI, two-seater) but WWI bipes had a very light structure. The Ag-Cat 164B is obviously a much more substantial aircraft and would be expected to be a bit more aerobatic. Still, I can't imagine that you'd need more than around a 125 to power a model with scale flight capabilities.
Keep in mind the long nose moment. Last thing I need is to add addiotional weight to the tail for balance.
All the more reason not to over-engine your model.
4 Strokes? OK, who makes the lightest and most powerful for this particular application. Don't forget my interest in a three blade prop.
I'm a Saito fan, myself. Good, strong, reliable engines with a sweet, sweet sound. Be aware that you won't be able to swing a scale diameter 3-bladed prop on ANY traditional 2- or 4-stroke model engine. However, with it's novel design the RCV engine can turn a much larger diameter prop.
http://www.horizonhobby.com/Products...rodID=SAIE125A