Re: Just curious, how are/were motors rated?

[David Stanton]

I’ve got an old 2-page magazine ad for the Johnson line from 1957 that claims all HP that year was measured at the propshaft. Not sure what they used to measure it.
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Some years later, OMC and Mercury all went to the engine block to measure it on most models and in the mid to late 1980s, models went back to the propshaft measurement to compete with motors from Japan, and that’s why the 9.9 Mercs (1986 up) and 9.9 Johnsons from somewhere in the late 1980s up will run circles around their 9.8s and 9.5s, and even the early 9.9 Johnsons, before they added tuned exhaust to boost HP.