What should be the perfct engine for hobbico extra 300S- super tigre 91, Tower hobbies 75 or O.S. 61 FX?
The super tigre is the powerfull one, the T.H. 75 is the cheapest , but I think they can't beat
the reliabilty of the OS, and it's power is enough for this 40-60 airplane. What do you think?

I see this is fairly old, but I would go for the tower 75. Is supposed to be very powerful, and I believe it's close in weight to the os .61. I have a 91 four stroke in mine and it will blast straight up, but I had to add noseweight with the 4 stroke. 2 stroke will be worse. I suggest building a battery box on the firewall and putting the battery up there( what i eventually did). This will keep it light as well as within the cg. It can be tail heavy, but believe me, the second it is out of it's limits, stability is gone.

Thanks for your advice, but I didn't succeed to buy this plane.