A SWAG--- probably start with some 26x10 stuff -
This size is not to small for any 100 class engine -if you are doing 3D stuff where the engine really neva gets a chance to unload .
it also keeps em from going up in smoke from simply being overpropped.
(Now some one will bring up their XXXX engine which sheds blades on anything under a 30 x10 --)