rbbiggs wrote:115hp burned 3.6gph at 3500rpm 24.1mph 6.69mpg, range 133.. Top speed 47.8
90hp burned 2.1gph at 3500rpm 17.6mph 8.38mpg, range 166.. Top speed 41.9.
That you have now provided some data to compare the 90-HP and 115-HP engine allows for an actual comparison to be made between these two Suzuki engines and their fuel economy.
To make a proper comparison of the engine fuel efficiently from the data selected for comparison there is a hurdle to be overcome: in the data provided the two engines are NOT performing the same amount of work. The 115-HP engine is working much harder as it is propelling the boat at 24.1-MPH, while the 90-HP engine is producing much less work, as it only moves the boat at 17.6-MPH.
We can made an adjustment for the difference in the amount of work being performed by using the boat speeds. It is well known that the relationship between boat speed and horsepower is to the 0.5 exponent, that is, the boat speed varies with the power ratio to the 0.5-exponent.
In this case the boat speed ratio in 24.1 / 17.6 = 1.37. This suggests that the power ratio must have been 1.875, that is, the 115-HP engine was making 1.875-times more power than the 90-HP engine. Now we can compare the fuel consumption figures.
The 90-HP engine consumes 2.1-GPH making its reduced power, and the 115-HP consumes 3.6-GPH making its 1.875-times more power. If we compare the fuel burn figures we see they are in a ratio of 3.6/2.1= 1.714, which means the 115-HP engine is actually running more efficiently as it makes 1.875-times more power while only consuming 1.714-times more fuel.
I don't think your intention by presenting this data was to demonstrate that the 115-HP was more fuel efficient, but that is what the data indicates.
rbbiggs wrote:Any better real world non pedantic ideas on these old whalers, I'm all ears.
I hope you were listening to my comments in this reply. Using actual data and actual physical relationships is not particularly considered to be pedantry by most people, although today the use of mathematics and physics might seem so to some.
What also has been demonstrated in the data provided is that operating the boat at lower speeds tends to reduce fuel consumption, but this relationship was already well known.