Can someone explain how my Yanmar 3GM in one boat is rated at 20 HP and in my new to me Hunter 33.5 the Yanmar is rated at 27 HP? They are both 3gm do they have different HP pumps? Or?
same model engine but different HP
- Thread starter Don Crowther
- Start date
Mine is rated at 22.5 hp. That is what the data sheet says that I received when we bought the boat. Further research is needed. Mine has a 72 mm x 72 mm bore x stroke. Someone told me once it has sleeves in the cylinders. Were later models built with out the sleeves? That might account for a hp increase.
The 3 HM is rated for 27 hp continuous, 30 max, one hour. It has a bigger bore/ stroke and displaces 1126 cc versus the GM 879cc. They look identical on the outside.
Somebody (maybe the great Smokey Yanick?) said " the only way to beat cubic inches is with more cubic inches."
3GM isn’t the full model number; the full model is either 3GM20(F) or 3GM30(F). As others have suggested the bore and stroke are different between the models, providing the extra power.
Edit:Upon further looking, the 20 hp model is just 3GM, not 3GM20. The later YM series uses the 20/30 in the model name.
Edit:Upon further looking, the 20 hp model is just 3GM, not 3GM20. The later YM series uses the 20/30 in the model name.
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In general terms manufacturers can change the HP rating of an engine series by changing the fuel delivery (pump and injectors) and the air availability (intake and exhaust). The same bore and stroke can produce a wide range of power output within a certain limit. If you increase the fuel delivery you have to intake and exhaust more air. Usually this can be done by adjusting valve sizes, manifold sizes and possibly valve lift. Obviously, if the engine produces more power then the fuel consumption goes up.