If you're not flying class, or if you have a good poker face, the new Thunder Tiger Pro .36 is the same exact dimensions as the .25, only bored out slightly. This not only gives it more power, but it is actually lighter than the .25. My buddies Slasher with this engine and a mack muffler tears up the sky.

Be sure to upgrade the ply reinforcement on the ailerons where the pushrods attach, they'll rip right off the control surface.