I have an OS 91 FS in an Ultra Stick 60 and a Thunder Tiger 91 FS in an Hobbico Extra 300 60. Both planes have have been flown A LOT, and have been abused (= crashed from time to time). Both power plants swing a 14x6 propellor efficiently. I have found both power plants to be reliable, and powerful enough for their respective applications. They both have had problems ... the OS lost a valve spring after one season and TT stripped a tappet set nut, also after one season. (OS charged me about 70$ to replace the spring while TT sent me the nut for free) The TT is a smoother running engine, but a bit heavier... and for the money, I think is an excellent engine; I would purchase another.

In addition, I have a Magnum 80 FS over-powering a GP Texan and a Magnum 52 FS in a Slow Poke. I have found the Magnum 80 engine to be easy to operate and reliable athough not as "pretty" as the OS or the Saito FS engines I also own. If one had the Magnum completely enclosed, I doubt anyone could tell the difference between it and an OS engine. The Magnum 80 has been in use for one season so the jury (in my mind) is still out on it. I really HATED the 52 FS until it got broken in. Now, after 3 seasons and many many flights (I like the Slow Poke) it is a sweet, reliable, easy to feed and use engine, and swings a 12x6 prop in one of my favorite planes.

I think the engine you choose really should depend on your application, pocketbook and your level of experience. If you are very experienced and working with a high performance airplane where every extra oz may have a deliterious on performance, then spend more and get the lightest and most powerful engine. But if you just like to fly, it is certainly possible to get adequate, reliable performance without breaking the bank.

All manufacturers make a boo boo once in a while so it is important to work with them if something is not right. Usually they will make things right. Be patient while breaking in an engine (especially a ringed engine, they take longer) and I believe you will be pleasantly surprised with what ever engine you choose.

PS: Thunder Tiger makes a nice, good looking 54FS. I have one of these in a Koysho Super Stearman. It gives me good, reliable scale-like flights.