It's an interesting situation.

Although you can buy a TT61 for the price of an OS46, I'd rather have the OS since the TT61 produces only marginally more power but weighs a whole lot more.

In fact, the whole justification for a 61 sized engine is becoming marginal now that you can buy engines like the TigerShark 56 which are only 0.04cubic inches (less than the size of a little Cox babee) smaller than a 61 but weigh the same as an average 40-sized engine.

With a 61 you end up hauling around up to 1/3 more weight with just 1/5th more power -- and you pay more for the privilege.

I've also heard that the OS91 is not their best engine -- and having seen one run this weekend I have to agree. They're not particularly powerful and the one I saw was totally put to shame by an ST90 that was being run-in in the air so was clearly not tuned for anything like max rpms.

The SuperTigre started easy, was very quiet, throttled great and really put out some power -- at just over half the price, that's the engine I'd be buying rather than the Thunder Tiger -- oh hang on -- I did buy one :-)