ameyam, the thread on the Reactor has lots of good info on these different engines in a Reactor but to surmise: a .46-size two stroke is marginal for 3D, as are the .70 class 4-strokes. The Saito .82 or OS .81 work well, as does the .91 Saito, in the Reactor anyway. If you have a lighter profile type plane, the .70 4 stroke would be fine. I have a Saito .82 in my Reactor, and it works well.