IO-346 with IO-550 cylinders

nrpetersen said:
The slightly longer stroke (assuming new pistons that might be heavier?) will slightly reduce the first mode natural frequency of the whole driveline.

They all (i. e. the natural frequencies) tend to be around 220 Hz which is the fourth harmonic for 2200 rpm. At cruise I could hear it in our 172M as a ringing just below middle C on a piano (which is 256 Hz I recall). The O-320s are not as hard on props and cranks as the O-360s per dinner talks with a McCauley engineer, but the 4 cylinder Continentals would probably be in the same range of concern.

6 cyl engines are more complex and involves multiple modes as I understand.
Click to expand...

What longer stroke? Crank remains the same, connecting rods as well. What you end up with is improved combustion chamber, valve position, runner flow, and possibly compression.
 
Henning said:
What longer stroke? Crank remains the same, connecting rods as well. What you end up with is improved combustion chamber, valve position, runner flow, and possibly compression.
Click to expand...
(and post by Thorpe above)
Yes obviously if the crank remains the same, the bore would have to increase for the larger displacement. My bad.

Same issue though. The pistons may be heavier. But casual "minor" changes to an engine can affect the propeller drive line dynamics, and are best left to experimentals or approved by an obviously knowledgeable source.
 
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