Fuel Economy

[dpearson]

One of my recent projects included wiring the Fuel Injection controllers to the boat computer. The project is still a work in progress, but I though you might be interested in some fuel economy measurements.

First some background. The engines on Buster are Volvo Penta 4.3 GXi fuel injected V-6's. The engines have GM Marine Electronic Fuel Injection (MEFI) version 4 controllers. The MEFI controller was designed for Marine use, but it appears to be a favorite of the high-performance car and truck people. As a result, there is a lot of information on the web about the controller and there are relatively inexpensive tools and software to mess with them. The connector and software package I am using is MEFIScan (http://www.mefiburn.com/mefiscan.asp) and was $195 per engine. It gives the ability to display almost anything the fuel injection system knows about. One of the most useful outputs of the system is fuel consumption. The computer provides a display in US Gallons per hour. If I combine this with speed readings from the GPS and a bit of math, I get some interesting results. It is a little imperfect as I can only read one engine at a time, so I have to assume that if both engines are running at the same speed that they should both be consuming the same amount of gas. Below is a summary of fuel consumption at a few different speeds. I read speed in Knots and have converted the fuel measurement to Imperial Gallons. Then for fun, I converted to l/100km so you can compare with your car.

Code: Select all

Speed      NMPG       l/100km
5.0          2.7           91
5.7          2.5           99
6.4          2.4          103
8.6          1.6          151
21           1.3          190
32           1.0          237
5.1          3.6          67.2  <-- running on one engine

Conclusion - Boat fuel economy sucks. Conclusion #2 - Go slower.

[sandrin]

Hello,

interesting data. Being on the market for an alcan 370, i did take some data over the internet about boat fuel usage, hp and milleage.I did find 4.3 vortec power curve and a site called boat fuel usage give idea of fuel consomption at a given RPM. i melted all these data to create that somehow imprecise ( particulary HP at 750 , 1000 rpm and over 4000 rpm ) spreadsheet. Then used the data you published on BBuster speed VS rpm to get the result you can see.

My result give something similar to yours, but im kind of surprise that your fuel usage is so linear. I would have tought that there was to be a sweet spot at around 3500 rpm giving the best fuel efficiency. Im curious about the ratio of your SX outdrive. Recently i had the chance to see another alcan 370 with the same power configuration (4.3 GXi) but i was surprise to see a 17 inch pitch on these aluminium 4 blades props, the SX outdrive had a ratio of 1.79 . I didn't try it, but he was claiming similar performance to yours, but no cavitation a low speed).

I did a similar sheet for the 5.7 and it show similar fuel usage by HP. ( the 5.7 use more fuel at lower HP but less in higher HP(200+) ). So I guess for the 370, 4.3 is a good economical choice.

sorry for my english, it' my second language.

the speed is shown in MPH not knots

[dpearson]

Nice analysis! I think once I get more data points that you will see the sweet spot around 3500RPM. I was more interested in the displacement speed fuel consumption as I was trying to figure out just how far we could go on our fuel supply. I need to take some additional readings to fill in the gaps. I will see if I can do that over the weekend.

With respect to props and gearing, I am a little uncertain. I think the gears are 1.89:1, but I don't have an easy way of confirming that. The props are 15.25 x 21 4-blade stainless, but these may not be optimal. During the repower, I could try all the props that I wanted, but only those in the Volvo Penta catalogue. None of the aluminum props worked, and the only prop that was close was a 14 x 23 3-bladed stainless. When I selected the larger diameter Mercury 4-bladed prop I only had one shot at it, so I guessed at 21" pitch and took my chances.