Cruising RPM 2QM15

[jim logan]

Ireally enjoy your informative answers, Perhaps you can settle a long-standing question of mine. Is the rated rpm of the 2QM15 3000 rpm, and does that mean that 3000 rpm is the one hour rating? That would mean that 80% is 2400 for long-term use. Mine seems to work better at 2500-2700, no overheat, no smoke, less vibration - since the 2QM15 and the 2GM are so similar, can the 2QM15 (that is in good shape) be run closer to the rated rpm?

 

[Gordon Torresen]

2QM15 ratings

The 2QM15 is rated 15 HP at 3000 RPM.Oddly enough, the spec says that the continuous rating is 14 HP but again at 3000 RPM. 3000 RPM is where your tach should top out at full throttle, in neutral. (Not too long please) Try it to check your tach and governor. If you get a different number, check your tach with a good hand held tachometer. If the tach is accurate, your long term RPM should be around 2400. A little more won't hurt. If your boat speed is less than you like at the prescribed RPM, you might want to tweek the prop. With the 3000 RPM rating, your prop should start to load things down at about 90% or 2700. I don't know if HP at lower RPM changes the rules of thumb. The G series engines are rated at 3600 RPM. The HP comes at higher turns and the engine weighs 100 pounds less.The HP equation has something to do with oomph and time, ie: move faster, push less.

 

[Stuart Lamb]

2QM15 Experience in a J/30

Greetings,I agree with all said so far here. On my '79 J/30 I found my QM15 with Martec folding prop to run the boat at proper speed through the water at about 2100 or 2200 RPM. Sometimes, when late to the starting line, we would put the hammer down to 2400 or 2500 rpm but anything more caused white/blue smoke out of the back and no real benefit. I'm guessing this was the prop on the boat but the law of diminishing returns was certainly a factor and speaking with a Yanmar rep once they confirmed, as Mr. Torrensen has stated, that the QM15 is a much lower reving engine than the later model GM's.