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post #25 of Old 04-17-2013
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Re: Overpropped; What to do?

Originally Posted by sony2000 View Post
In quoting me you dropped the word "overall". This term is to encompass efficiency related to
1. maximum range on available fuel.
2. a level of RPM that causes above normal wear on the engine.
3. time to destination.
4. maximum torque.
5. hull speed.
An over propped engine ends up operating at a higher manifold pressure, resulting in a more frequent, destruction of head gaskets.
I am confused here. You talk about manifold pressure. Now this is relevent to a superchrged or turbocharged engine but NOT a normally aspirated diesel as there is no form of restriction to the inlet manifold opening; it runs wide open all the time.

Also I do not see how time to destination figures into this. I wonder if you are using data from an aircraft fitted with supercharged petrol engine fitted with a device to control mixture strength and boost pressure plus a variable pitch prop.

Finally in my experience almost all cylinder head gasket failures can be traced to engine overheating from coolant failure, some are corrosion related.
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