Can someone please tell me what the largest size engine will fit into a stock 30 helicopter.
There have been people putting a 90 engine into a raptor which was originally a 30 size.
An OS50 gets in there without modifications (well, some parts to adapt for other hole positions etc)
But to make proper use of a larger engine you need larger blades. And larger blades need larger boom. At some point bearings start to wear quicker than should. For instance the V1 trust bearings broke down quickly with 50 size blades.