Why?
I dont know that is why i was asking. As I said throughout my training I was always taught not to go over square.
I think what they were getting at was that if the MAP is too high, excessive pressures in the cylinders could lead to detonation and engine damage.
I suppose though that if you stick to the POH this shouldnt happen.
As I said I dont know, it was just what I was taught "Dont have MAP higher than RPM"
In fact the latest advice I have received is that:
If possible, it is better to operate with a high MAP and low RPM when cruising because:
- low rpm means - increased volumetric efficiency, less frictional loss and lower mechanical loads on the reciprocating parts of the engine, less noise and vibration in the engine
- high MAP, achieved with a wider throttle opening means less restriction to the airflow throughthe throttle butterfly valve in the carby, which contributes to better volumetric efficiency. There is less frictional loss of energy in the airflow during its passage through the inlet manifold.