i have cmpro katana 50 with os 46 ax. but i dont like engine performance, which engine is good for katana?

Well, a good choice would be a 50 range engine, and I reccomand the OS 55 AX which is almost as light as 46 and more power full.
I used on it that engien with APC 13x4 W prop and it was enough power.

to Your attention, this plane is quite heavy for it's size and has a very small wing area so it's really hard to 3D it, but it's nice areobatic plane.
try to keep this plane as light as possible.

you Could also use 82 four stroke but I think it's heavier than the 55.


Guy.

i am thinking to buy a os 70 surpass II 4 stroke. what are you thinking about this engine?

The plane balances fine with a Saito 82 and you have ample power for aerobatics. If you were to look for the review is either RCU or RCG they flew 3D with a simple 52 sized 2C engine. I am sure she will fly fine on the OS70