CONTINUOUSWAVE

During the dealer meeting in 2014 when Evinrude revealed their new E-TEC V6 74-degree engine, a slide was presented that showed the brake specific fuel consumption of the new engine at various loads. The slide looked like this:



In this bar graph presentation, a lower bar is the better value, as the data is for rate of fuel consumption, and lower fuel consumption is better. (Note that the legends "High Speed" and "Low Speed" are reversed in this slide from the actual speeds.)

This is a very interesting slide because it gives the exact data values for each bar on the graph. Let us concentrate for the moment only on the E-TEC G2 or 74-degree V6 engine data, and extract the data from the slide.

Specific Fuel Consumption in grams/kW-hour

E-TEC G2 250 H.O.
MODE 1 = 284
MODE 2 = 268
MODE 3 = 296
MODE 4 = 336
AVERAGE= 293

Now we need to convert g/kW-hour into lbs/HP-hour, a more familiar dimension for fuel consumption (at least for me). We develop the conversion factors:

1-gram = 0.002204622622-lbs
and
1 kW = 1.341-HP

The conversion factor is therefore

0.0022-lbs/1-gram / 1.341-HP/1-kW = 0.001642 (lbs/g) / (HP/kW)

Recalculating the fuel consumption into lbs/HP-hour

E-TEC G2 250 H.O.
MODE 1 = 0.466
MODE 2 = 0.440
MODE 3 = 0.486
MODE 4 = 0.552
AVERAGE= 0.481

In the slide the data is noted as being for the engine operating at certain loads according to the defined modes in ICOMIA 36-88. Those modes and their weighting factors in terms of portion of total engine operating time are:

MODE 1 = Idle; 0.40 of total time
MODE 2 = 0.4 of maximum; 0.25 of total time
MODE 3 = 0.6 of maximum; 0.15 of total time
MODE 4 = 0.8 of maximum; 0.14 of total time
MODE 5 = maximum; 0.06 of total time

Note that in the presentation, no data was given for MODE 5 fuel consumption, but that mode represents only 0.06 of total engine running time in the ICOMIA model, which is typical of actual use by boaters.

The illustration says the "average" is 293. Let's see if we can come up with that number and find the missing MODE 5 data.

The proper weighting method is to apply the fuel consumption according to the time weighting, so we would have:

284 x .4 = 113.6
268 x .25 = 67
296 x 0.15 = 44.4
336 x 0.14 = 47.04

TOTAL = 272.04

If the "average" is from weighted ICOMIA factors, then to boost 272.04 to a composite weighted average of 293, the missing factor would have to contribute 20.96 to the total. Since that is weighted at only 0.06, the missing data would then have to be

20.96 / 0.06 = 349.3

That seems like a very reasonable factor for fuel consumption at full throttle because it is consistent with the values and trends at lower throttle setting, that is the fuel consumption is tending to increase with increasing throttle. We can then make a reasonable assumption that the E-TEC G2 250 H.O. fuel consumption for all five ICOMIA modes would look like this:

E-TEC G2 250 H.O.
MODE 1 = 284
MODE 2 = 268
MODE 3 = 296
MODE 4 = 336
MODE 5 = 349
AVERAGE= 293

Converting to lbs/HP-hour:

E-TEC G2 250 H.O.
MODE 1 = 0.466
MODE 2 = 0.440
MODE 3 = 0.486
MODE 4 = 0.552
MODE 5 = 0.573
AVERAGE= 0.481

There you have it: comprehensive data about the fuel consumption rate for the Evinrude E-TEC G2 250 H.O. engine. I suspect that it is reasonable to apply these same rates to other models in the V6 74-degree line, inasmuch as the fuel consumption rate is allotted by horsepower.

It is also interesting to note that the Evinrude E-TEC G2 or 74-degree V6 engine delivers its best fuel economy at ICOMIA mode 2. That is at an engine speed of 0.4 of maximum. If we figure maximum is roughly 5,500-RPM, then mode 2 speed is around 5500 x 0.4 = 2,200-RPM. This suggests that when running in that approximate engine speed range, the fuel economy of the E-TEC G2 is going to be outstanding--even better than at idle speed.

The problem with 2200 RPM is typically it falls in the transition region where the boat is getting over the bow wave and on plane. Now if they were to put the E-TEC in a car with a multi-speed transmission, they might try to gear it to run 2200 RPM at say a 60 MPH cruise speed to maximize fuel economy.

There is an old standard for a rule of thumb for estimating outboard engine fuel consumption, dating back to the days of the conventional two-cycle outboard engine with carburetors, that says the fuel consumption at full throttle in gallons-per-hour will be the horsepower divided by ten. For example, a 250-HP engine would consume 25-GPH at full throttle. With the data on the E-TEC 74-degree V6 engine rated as a 250 high-output engine, we also got a slide giving us a graph of horsepower at various engine speeds.



In this graph the data values are not given, so we have to interpolate between the Y-axis lines to get the horsepower. To make this easier, I have made an enlargement and added a line at 275-HP.



We can see that the E-TEC 250 H.O. 74-degree V6 engine is making 275-HP. Since we know its fuel consumption (from the other slide) we can make a new rule of thumb for modern engine fuel consumption, based on this data. We take the horsepower value and use it to get a fuel consumption rate. We figure that gasoline weighs 6.25-lbs-gallon, and we use the MODE 5 specific fuel consumption data:

0.573-lbs/HP-hour x 1-gallon/6.25-lbs x 275-HP = 25-GPH

For the rule of thumb factor:

275-HP / 25-GPH = 10.9 rounded up to 11

Now we have a simple rule of thumb for fuel consumption of modern outboard engines at full throttle: divide HP by 11 to get GPH

jimh wrote:There is an old standard for a rule of thumb for estimating outboard engine fuel consumption, dating back to the days of the conventional two-cycle outboard engine with carburetors, that says the fuel consumption at full throttle in gallons-per-hour will be the horsepower divided by ten. For example, a 250-HP engine would consume 25-GPH at full throttle. With the data on the E-TEC 74-degree V6 engine rated as a 250 high-output engine, we also got a slide giving us a graph of horsepower at various engine speeds.

ETECG2HPComparisonCropSmall.jpg

In this graph the data values are not given, so we have to interpolate between the Y-axis lines to get the horsepower. To make this easier, I have made an enlargement and added a line at 275-HP.

ETECG2HPComparisonDetailCrop.jpg

We can see that the E-TEC 250 H.O. 74-degree V6 engine is making 275-HP. Since we know its fuel consumption (from the other slide) we can make a new rule of thumb for modern engine fuel consumption, based on this data. We take the horsepower value and use it to get a fuel consumption rate. We figure that gasoline weighs 6.25-lbs-gallon, and we use the MODE 5 specific fuel consumption data:

0.573-lbs/HP-hour x 1-gallon/6.25-lbs x 275-HP = 25-GPH

For the rule of thumb factor:

275-HP / 25-GPH = 10.9 rounded up to 11

Now we have a simple rule of thumb for fuel consumption of modern outboard engines at full throttle: divide HP by 11 to get GPH

This newer rule of thumb seems to work for most modern naturally aspirated fuel efficient outboards. The supercharged Mercury Verados are closer to the old "10 rule of thumb".

For supercharged engines, maybe divide by 9 is closer.

For the first generation Verados, perhaps 9 worked but the estimate for the latest generation seems to get close with 10. It seems intuitive that at some point the benefit of the supercharger at lower RPM has to come with a cost at the higher RPM.

Do we have specific fuel consumption information on the Verado family of engines? It would be interesting to compare the Gen 2 engines in both the L4 and L6 blocks.

There are at least two companies specializing in tuning Verado engines by modifying the ECUs. It is interesting that the modifications can be customized to a high degree for power output. Most clients want the tuning to be for the use of premium-fuel while others are constrained to mid-grade or regular fuel. The reviews I've read have all been from customers who wanted tuning for increased horse power but I know of no reason the ECU could not be adjusted for maximum fuel economy at a specific RPM range.

Apparently there is little concern for maximizing Verado Gen 2 engine output because of the Verado knock sensors.

Most surprising to me is the modest improvement in fuel consumption at full-throttle in the modern engines compared to the traditional engines. Many people think that modern engines are achieving a miracle in reduced fuel consumption, but they are not doing it at full throttle. The big improvement in fuel consumption for modern engines compared to traditional engines occurs at lower throttle settings. In contrast, the traditional engines were probably the most fuel efficient at full throttle. The modern engines are much more fuel efficient at lower throttle settings, and that's where a recreational outboard engine spends almost all (94-percent) of its time running.

Good data from manufacturers about outboard engine horsepower, torque, and fuel consumption is hard to obtain. We only have the data used in this discussion because someone in the audience at the dealer reveal snapped a picture of it. I don't think these graphs have been published elsewhere by the manufacturer.