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In another thread somebody brought up the props driving engines topic. Rather than continue down a side thread, I thought I'd start a new one (and food fight). I started thinking about the topic after I read it on the other thread. It has to do with descents at low MP with high RPM. The argument is that doing that creates a big negative pressure above the piston which may pull the rings up off the landing during the intake stroke only to have them slammed back down during the compression stroke, thus creating flutter and potential ring/landing failure. So how low can the MP be or how much spread can be allowed before this happens? It hit me. You MUST have SOME reduced pressure above the piston or no new fuel/air mixture will flow into the cylinder during the intake stroke. How much is too much? I don't know. However... If I'm cruising at 12,500' in my NA '78J, the maximum MP I can get is something around 17" of MP, maybe lower depending on the air filter. If I'm cruising at that altitude using 2600 RPM to get as much speed as possible, what's the difference between that and using 2600 RPM with the power pulled back to 17" during a descent at lower altitudes? Nothing. Pressure is pressure. It doesn't matter whether it gets that low because of my altitude or because I've choked the airflow with the throttle. If 17" at cruise doesn't cause flutter, neither should 17" in the descent. The mighty J has a service ceiling of around 18,000' where the MP would be about 15" or less. If I can theoretically cruise at that altitude and MP, I feel pretty comfortable using 15" during a high RPM descent. Might just be me though. Let the games begin...