What is the most efficient cruise RPM for Mercruiser 140?

[fishnfiend]

Have an '86 Mercruiser 140, Alpha One with 15.25 diameter, 15 pitch prop. At 22 mph (the speed at which son likes to wakeboard), the motor is running around 3100 RPM. Is there a range (higher or lower) that would result in better fuel economy and be better for engine, or am I in the ballpark?<br /><br />Thanks for any information. Gas is heading above $3/gallon around here, and don't want to drink any more than necessary (gas, that is).

 

[tommays]

Re: What is the most efficient cruise RPM for Mercruiser 140?

your in the ballpark <br /><br />without a fuel flow meter you never realy no the exact best point<br /><br />RPM MPH MPG <br />2500 17.8 6.23<br /><br />3000 24.5 6.35<br /><br />3500 29.3 6.10<br /><br />these are from a test on a 3.0 and there seems to be a 1000 rpm range were the MPG is about the same<br /><br /><br />tommays

 

[whywhyzed]

Re: What is the most efficient cruise RPM for Mercruiser 140?

If you are wakeboarding, you aren't seeking more mpg, you want less fuel burned per hour. So the slower you go, the less you fuel you will burn. It's pretty much a linear relationship. (rpm to fuel consumed). Of course vacuum is the inconsistent part.<br /><br />As far as 3100, the engine is loving running at that rpm. You're just getting into the bottom part of the torque curve where the engine is most efficient at turning the crank. Torque peaks around 3700.

 

[whywhyzed]

Re: What is the most efficient cruise RPM for Mercruiser 140?

Originally posted by tommays:<br /><br /><br />RPM MPH Knots Total GPH MPG NMPG Range NM Range dBa <br /> 800 4.0 3.5 0.6 6.67 5.80 108 94 66 <br /> 1000 5.3 4.6 0.8 6.63 5.76 107 93 68 <br /> 1500 6.5 5.6 1.2 5.61 4.88 91 79 71 <br /> 2000 8.1 7.0 2.4 3.43 2.98 55 48 78 <br /> 2500 17.8 15.4 2.9 6.23 5.42 101 88 79 <br /> 3000 24.5 21.3 3.9 6.35 5.52 103 89 79 <br /> 3500 29.3 25.5 4.8 6.10 5.31 99 86 80 <br /> 4000 33.8 29.4 6.7 5.08 4.42 82 78 88 <br /> 4500 39.1 34.0 8.4 4.68 4.07 76 66 93 <br /> 4900 43.7 38.0 12.3 3.55 3.09 57 50 94 <br /> <br /><br /><br />tommays

cool- where is that data from?

 

[fishnfiend]

Re: What is the most efficient cruise RPM for Mercruiser 140?

Thanks for the awsome data! Looks like I'm propped about right for this purpose. Once again, this board rules.