1974 Merc 20 HP

[NathanY]

In this year model where these engines rated at the prop or at the crank? If at crank then about how many hp is this engine. I was told my many people that the older mercs where notorious for being over rated, ( 9.8 is really about 12, and 15 is really about 17 and so on) is this true? One source of this is my father who was a merc master tech for 15 years. Any who can anyone riddle me this?

 

[steelespike]

Re: 1974 Merc 20 HP

NathanY,Your dad is right but the term would be under rated ie: a 10 would be more like a 12 etc. By the 70s they were more normally rated.Approximately 1985 manufacturers started rating at the prop.<br />Your motor is rated at the power head.The rating<br />at the prop would be approximately 10% less.You<br />will see figures as low as 5% and as high as 12<br />or 15% but I think 10% hits it pretty good and its easier to do the math.About 18 at the prop.