ORIGINAL: Nathan King
ORIGINAL: ChuckW
If you can still find one, a YS-63 will fly that plane as well or better than the .46 2-stroke and still be lightweight. It is being replaced by the YS-70 however which of course would be even better.
Beyond that, any good .70-.82 4-stroke will be excellent. If you can find a discontinued OS .70 Surpass-2 it would be a great choice. There new ones would be too.
That's a heck of a lot of power for a 40 sized airframe. May I suggest model rocketry?
I'd personally go with a Saito 56 and be done with it.
Nah... A YS-1.10 would be overpowered. I've actually seen people suggest that sort of combo too on a 40 size plane. Makes no sense to me. The little .63 will be equivelant of something like a Saito .82. Maybe not exact of course but similar. Plus it is fairly compact and lightweight.
I also agree on the .52-.56 though depending on how you want to fly it. They'll do better than a person might think.