I ran it up today without a muffler. Loud, but it popped off easy once the fuel got to it. Throttle response was decent or better from what I can tell. I think I need to prop it down some as 14" is a little much I think. Power seemed good though although I have no way to check RPM's. I doubt it's putting out as well as some hi-performance engines, but I imagine on a plane rated for a max of 1.20 that it will perform well.