Does Less Horsepower Equal More Fuel Economy?

[@alexanderscott2567]

I have my outboard maxed out on the ecu with a digital tune. I modulate the efficiency the old fashioned analogue way, i.e. throttle control. If you had to, you could detune the ecu. Even easier, just stuff a dirty old sweatsock into the airbox.

[@FlatlanderGear]

These things aren’t predicted linearly but I can say these things: 1. More cylinders tends to result in more mechanical friction in the engine. Idle/trolling fuel economy using similar parts between two different engines, will be different between a V6 and V8 with similar cylinder displacement. The V8 will burn more fuel idling and trolling. 2. Knowing this, with equivalent propping, the larger displacement engine with more cylinders will usually burn more fuel for the same trip than the smaller displacement engine at low loads and engine speeds. 3. At mid range, this will tend to flip in a lot of cases. The larger displacement engine may burn less fuel at cruise because it will tend to spin at a lower rpm at a higher torque than the smaller displacement engine, resulting in less friction and heat for the same shaft horsepower produced. 4. At high loads, with equivalent parts, a similar trend as #4 is seen until you exceed the applied hp of the smaller displacement engine. 5. Any deviation from these is a result of hull design, differences in engine weight, different engine brands, drastic differences in engine construction, 2 vs 4 stroke, motor age, motor condition, propping, lower unit ratios, fuel quality and many more.

[@andronclock1]

The best answer.

[@SkipSilvestrini]

One cannot compare automobiles and boats. Water is 800 times more dense than air without considering tides or currents or wind. Fuel efficiency depends on average weight of the boat. The same boat that typically only carries 2 people needs less HP than if it typically carried 6 passengers. More HP means the boat with more load can perform better. The bigger HP doesn't have to work as hard to achieve the same performance of the same boat with lower HP so will likely get better or similar fuel economy but will last longer as it simply doesn't have to run at as high RPM to gain similar performance.

[@ericdavi1231]

My 30 footer with twin 300s gets the same fuel economy as my friends 26 with twin 150s but is way faster!

[@rowanbr]

thats a good one