The normally aspirated 2nd gen engines were from 135-160 hp.  You
mentioned that it performs better than your old 160 hp Lyc; maybe you're
already getting all there is, short of a 2.85 redrive and retuning the
intake.

Charlie

 

If the engine is load limited RPM wise, then airflow requirements may have been satisfied at less than full throttle.

 

The idea of a slight nose down run to make that determination sounds realistic. 

 

Lynn E. Hanover