Years ago I flew a Bellanca Scout with a Lycoming O-360 engine rated at 180hp. I recall there was a yellow caution range on the tach going from approximately 16 or 1700 to 2100 or so (I can’t recall the exact range). I now fly an Acrosport 2 and Skybolt, both with IO-360’s, one rated at 180hp, the other 200hp. Neither airplane has an amber caution range on the tach. Does anyone know if there’s an inherent issue with this engine related to harmonics and/or vibration? I usually am not operating for long in this range but am curious as to how this possible engine limitation might affect over square engine operation for cruise flight.
