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Author Topic:   Interpreting E-TEC LOAD Parameter
jimh posted 06-15-2015 09:26 AM ET (US)   Profile for jimh   Send Email to 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 LOAD and HP

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.

Jefecinco posted 06-15-2015 10:26 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Does a comparison of load and fuel consumption also appear quite linear?

Butch

jimh posted 06-15-2015 10:36 AM ET (US)     Profile for jimh  Send Email to jimh     
BUTCH raises another method to deduce horsepower: use the fuel flow rate of the engine. The assumption in that method must be that the Brake Specific Fuel Consumption (BSFC) of the engine is constant across all throttle settings, loads, and engine speeds. From the outset, I don't believe that BSFC will be constant, but it might not be so variable that using it to deduce horsepower won't be sufficiently accurate.

What is needed for testing a model of correlating horsepower to LOAD using fuel consumption is a set of data.

jimh posted 06-15-2015 10:51 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is the data set I used to correlate LOAD to HP using boat speed:

RPM/MPH/MPG/LOAD
4450 29.0 2.5 37
4600 29.6 2.5 37
4800 31.3 2.5 39
5000 33.2 2.45 42
5200 36.1 2.38 46
5650 39.0 2.2 52
5900 40.5 2.1 58
6100 41.7 2.0 96

Data for GPH could be computed from that data by using MPH/MPG. The results would be

LOAD / GPH

37 11.6
39 11.8
42 12.5
46 13.55
52 17.7
58 19.3
96 20.9

There is a data set. Let us assume at 20.9-GPH we make 225-HP. This suggests the relationship between fuel and horsepower is 10.76-HP/G. Then we'd get

LOAD / HP

37 124.8
39 127
42 134.5
46 145.8
52 190.4
58 207.7
96 225

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