why is it not recommended to run manifold pressure on top of r.p.m. in a naturally aspirated piston engine? (for now just ignore super/turbocharged engines where higher m.p. is run regularly)
the numbers seem fairly arbitrary, eg. what does 25" hg have to do with 2500 rpm, etc. other than the numbers are referred to as 25 squared or 23/25 or whatever combo you like so it can appear as running one higher than the other even though they are different units.
i am referring mostly to the prohibition of running wide apparent differences in the numbers(like say 25" with 1700 rpm) since some manufactures do allow power settings where the manifold is 'higher' than the rpm but only by a small amount. for the sake of discussion consider a common engine like a lycoming O-360. you always get the warning but i've never seen it with a good explanation.
does it have anything to do with a greater volumetric efficiency from having a more open throttle putting a bigger charge of air into a cylinder, and with a lower rpm the crankshaft doesn't have the momentum to drive the piston to compress the greater chunk of air/fuel? and if that's it what is the result of running m.p. on top for a long time? jsut too much stress?
having asked all of that i wonder if the answer is apparent if you consider the difference in construction/setup of a boosted engine vs. a naturally aspirated engine?
high manifold pressure/low rpm
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what the f?
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