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  1. #1
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    HP difference between a 1978 115 T.O.P and a 1986 115?

    Seems like this is the year of motors for me. In addition to a 3.0L offshore 250 I picked up a 1986 Merc inline (grey stripes) motor. Serial sais its a 1986. I currently have a 1978 inline 6 on my 16' Baja. I bought it as the price was good and it has the integrated power trim as the 78 has the external pump and side cylinders. This should clean the back of the boat up a bit.
    I have read through a few good threads on here and understand that the "later years" had some improvements done and that they are really close in build to the earlier model 1500's? I have read different info that said it occurred after 1976, 1980, and 1985. Is there any difference in my 78 and 86 motors from a HP perspective? they are bot ADI so i thought other then trim they were the same? Paid $625 for the 86 115. compression is good, power trim works, looks in great shape....no spark. Ill get it on a stand and I am sure ill figure the spark issue out.
    79 Baja 16SS w/ 79 115 merc

  2. #2
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    In 1978 the motor was rated for hp at the crankshaft. In 1986 it was rated at the prop shaft.

    So, the 1978 is about 100 hp at the prop shaft while the 1986 is a true 115 hp.

    If heard the story correctly, it was Mercury that had the hp ratings made into law around 84, maybe 85. Merc would claim their motors at ** hp and then when tested they were significantly higher. They tried blaming it on the way they tested their motors, so it became standard to test all motors for hp at the prop shaft.

    Again, if I heard the story correctly, it was not long after the prop shaft testing was made standard Merc was found again to be under rating their motors so yet another standard came along that the motors must be within 10%, maybe 15 of what they were rated at. Of course they found another way to beat that, but that is part of what made them such popular motors.

  3. #3
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    Awesome. OK That's what I was hoping. So if this 86 is running like it should, I should see a small bump in power. Excellent. I think I heard that when the V6 150 came out they rebadged the 1500 to the 140, the 140 became the 115, and the 115 became the 90. Then when the standard rating came in around 84/85 the 140 got rebadged to the 115, etc and the shuffle happened again. So an 86+ is close in power to the old 1500... Not sure if that's really true though.

    Thanks!
    Last edited by SPIDERMONKEY; 05-04-2021 at 10:27 PM.
    79 Baja 16SS w/ 79 115 merc

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