Hey Fellers,
The history of inlines is on Scream n' Fly.
Mark is a bit wrong about the prop rating issue. Merc always underated their inline6s. That said: they did rate them at the crank 'til 1982 when they rated them at the wheel, (prop).
He is correct in that they were always underated vs other manufacturers. It was most dramatic in the 1950s butt: corntinued to the last year of the inline6s: 1988. Dunno 'bout the newer stuff.
The first production manufactured 100 HP engine, (also the first time Karl painted the VERY purdy ol' girls Black), was a very purdy 89.x cubic inch inline6 that was made from 1962 to 1969, (in 1967 they called it a 950) to differintuate a bit from the 94.x 110 HP engine.
The first 99.x cubic inch inline6 was the 1968 125 HP 1250, and after the 1969 model year all of 'em were 99.x cubic inches from the 90HP 900 to the 150 HP 1500. In 1970 they changed the 1250 block, (although still a "silver block") to the 1350 and the 1150, (it is fairly easy to make a 1970-72 1150 a 1350 with reeds n' minor mods to the carbs), THE ONLY TIME in the inline6 lineup you can make a modest change to increase HP, (the rest are best left alone as the factory was obsessed with testing and ya can't beat Karl at his best game).
Once Merc went with a bigger cubic inch v-6 they renamed the 1500 a 140, to differentuate from the 150 HP v-6.
In 1982 they went to prop ratings and the ol' 1981 140 was a 1982 115 and the ol' 1981 115 was a 1982 90.
The prop rated 1982 115 had less flow at the reeds then the ol' 1500 or the 140 so it had somewhat less HP. The difference between an 1982 90 and a 1981 115 is less clear ta me as I have not had those two apart n' I only have one functional brain cell.
I hope Ed from Pauslbo, Chris1956, or Laddies or some of the other big guns here on iboats will chime in ta tell us what the difference was between the 1981 115 and the 1982 90 as 25 HP is far more then the 8% to 13% difference from the crankshaft to the propeller.
Me overpriced $.02. JR
