I emailed the factory to ask "what is the limiting factor on Vne?". I got back a response that was polite enough, but basically said they would prefer not to answer. Then added that basically I would need to exceed the 240 bhp in order to even approach it. But I have some aerodynamic mods in mind, along with a turbo and a variable pitch prop, that might test that theory (stretching the service ceiling up to higher speeds in the flight levels). He attached a spec sheet from their brochure that didn't even have the Vne listed on it. It IS listed on their website as "175mph", but it doesn't say whether that is IAS or TAS. I asked that as well, but got no answer. Basically a "go away boy, ya botha me" (in my best W. C. Fields). Seems a little ham-fisted being listed as mph instead of knots. So, would anyone here be familiar enough with the CH640 to care and take an educated guess as to the limiting factor? Flutter maybe? The reason I jump to that conclusion is this video, being that it is basically just a home-built Cherokee 140.