Interpreting E-TEC LOAD Parameter

[jimh]

The E-TEC engine provides data about a parameter called LOAD which represents the throttle position on a scale of 0 to 100. I developed the following table of data from some observations I made of boat speed and LOAD. I assumed at maximum throttle and maximum boat speed the engine was delivering its rated power, 225-HP. At other throttle settings I deduced the horsepower by comparing the boat speed at a particular LOAD setting with the FULL throttle boat speed, and calculated the horsepower as a function of boat speed, based on the general concept that boat speed is proportional the the power-to-weight ratio to the 0.5 exponent. That is a reasonable assumption for a moderate speed planing hull boat.

Here is the data:

LOAD HP
37 111.1
39 126.8
42 142.6
46 168.6
52 196.8
58 212.0
96 225.0

If you plot this data, the plot looks quite linear, except for the LOAD = 96 point. This suggests to me that probably the engine hit maximum power somewhere less than LOAD = 96. Here is a plot:

Plot of E-TEC HP as function of LOAD

ETEC_Load_HP_Plot.png (38.04 KiB) Viewed 6862 times

From the data in the region of 37 < LOAD < 58, that is, the center portion of the LOAD range, it appears that one could predict the horsepower by the following relationship:

HP = Full-ThrottleHP x ( (0.025 x LOAD) - 0.425)

Testing that function at LOAD = 42 and Full-ThrottleHP = 225:

HP = 225 x ( (0.025 x 42) - 0.425)

HP = 140

This is in a good agreement with the deduced value of 142.6-HP. This relationship does not work if the LOAD is greater than about 60. That is because in the test data used to develop the equation, the full-throttle horsepower appears to be reached when LOAD is about 60. LOAD values above 60 would then suggest the horsepower was greater than the full-throttle horsepower, which is not valid. Similarly the proposed function would return negative values for horsepower when the LOAD was below about 15. Thus the function has a limit to its range of roughly 30 < LOAD < 60, or the mid-range of the LOAD parameter.