I'm running two OS .25 FX's on my scratch built Uravitch OV-10. I can't say enough good things about them. I have a lot of flights on the airplane with NO engine outs, both engines running within a few RPMs of each other always, and they throttle down very well for landing. Very powerful, easy to start, and they run very well here at our 3500 ft location. They don't seem to be affected by changes in humidity that my Thunder Tiger .46 gives me fits on. Living in Oregon, we get not only seasonal changes in humidity, but sometimes weekly changes . I have tried the OS LA engines on other planes, but they don't put out much power, so I would only look at the more powerful FX, especially with a warbird. Lee