Mercury Outboard HP rating

[Jason]

What year did Mercury start rating HP at the prop and not the powerhead?

[Rich_V174SS]

Probably in the late 70's early 80's when they switched from the distributor ignition systems and went with all electronic ignitions. I'd say my '83 Merc 115 is every bit what it says on the engine cover.

[wexrocks]

I've been told by certified merc techs, and numerous others that the larger models switched to prop rated in '85. I was curious about the same thing when shopping for outboards in the past, and that's the info I was given... Can't personally guarantee it though.

[Jason]

Wonder what the power difference is when measured at the prop. I know cars did the same switch in 1972-73 when they went to SAE net HP. I know the power difference was quite a bit but there are a lot more moving parts in an automotive transmission then an outboard plus I think cars were also tested with p/s pump, alternator, fan, ect too.

A 1972 Lincoln Mark IV with a 460 V8 was rated at 365HP gross. The same engine in a 1973 Mark IV was rated at 212 HP net. 365 to 212. That a big difference!

[wexrocks]

I was told my 175 evinrude (crank hp) supposedly puts out 140 at the prop, so I'm guessing they probably lose around the same percentage across the board. It's easy to tell when they switched with the evinrudes, because the new 175 got the old 235 bubble back powerhead after the switch, so it would be safe to say the old 235 is comparable to a newer 175... I think...

[Hyperacme]

I have heard 1985 to 1986 was the switch ...
Which ...I think ... is about the time Merc went to the new trim system.

Do a search on "Merc Outpost" .

http://www.fiberglassics.com/glassic-forums/mercury-outpost

http://archives.fiberglassics.com/forum917/

[V153]

Yup by '85 just about everybody was prop rated. Not to say as in Rich's case some manufacturers didn't start earlier.

Pretty sure my ole '86 90 is pushing near 90?

[74 Carlson]

1985-86 That happend. My inline on the pickel is a 1987 115 which is the same thing as the old early 80's 140 inline. The boat originally had a 1975 115 inline and the boat ran about 50-51mph, with the 87' inline It's been gps at 57mph with a 3/4 tank of fuel. I haven't had a chance to gps with an almost empty tank.