Was there a change in the way HP was measured in OBs? Did they change from powerhead to prop? If so that would mean my 1973 135HP was measured at the powerhead not the prop?
You are correct. All mfgrs didn't change at the same time (it was lead by the Japanese mfgrs). By the mid 80's, most motors were rated at the prop. About a 5 to 7% difference.
