From what I know of the stock 3D power system, it's just typical "300" style motor. It won't hold up to the voltage from a 3S LiPoly, which is okay, because a 340 LiPoly won't hold up to the Amps the 300 motor will draw. What you'll have is about 10 seconds of good power, followed by a drastic dropoff in power, ending in a forced landing or crash. This will happen about twice before the battery pack is too beat to do much of anything, and has to be tossed in the trash... If it's any consolation, the motor will never run long enough to get seriously damaged from excessive voltage.

Maybe some of you guys are successfully running the stock power setup on 3S LiPolys, but I doubt very many. A 2S LiPoly is much more practical, but you'll need two of those 340mAh packs in parallel to hold up to the Amps that he motor will be drawing.