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E-TEC Fuel Economy
|Author||Topic: E-TEC Fuel Economy|
posted 11-19-2005 11:54 AM ET (US)
I was at the Pacific Marine Expo in Seattle yesterday and stopped by the BRP Evinrude booth. They had a couple of the larger motors on display, one being the 225 H.O. The Area Representative working the booth seemed knowledgeable about the product. We talked specifically about a the 250-HP E-TEC compared to the older technology Yamaha 250-HP OX66 two-stroke EFI which I currently run. He asked me how I currently use my outboard: 90% of the time running at cruising speed, about 4,000=RPM. He indicated that E-TEC outboards were much more fuel efficient at low RPM and I could expect it be at least as fuel efficient at 4,000 RPM as my current outboard. Needless to say I was very surprised by that statement. I was under the impression the newer outboards were significantly more fuel efficient at all operating ranges. Has anybody seen hard numbers regarding fuel comparisons?
posted 11-19-2005 01:23 PM ET (US)
The greatest efficiency difference between the DFI 2-stroke outboards and the carbureted/EFI outboards is at low engine speeds and WOT where the carb/EFI outboards are running in their most inefficient zones. As the engine speeds increase up to a point, the percentage difference decreases because the conventional 2-strokes actually become more efficient (less unburnt fuel passes out the exhaust port). In the case of the DFI 2-strokes, the efficiency does not appreciably increase across the operating spectrum like it does in the case of the conventional 2-stroke because there is essentially no unburnt fuel going out the exhaust port at any engine speed.
The most efficient zone for the Ox66 is in the 3000 to 4000 RPM band. At 4000 RPM, your Ox66 burns about 12 to 13 GPH. See www.yamaha-motor.com/assets/products/otb/bulletins/bulletin_otb_2StrokePerf_OX666_250hp_01104-GRW-Z.pdf . At 4000 RPM, an E-TEC 250 will burn about about 12 to 13 GPH also. See http://www.e-tecinfonet.org/sitebuildercontent/sitebuilderfiles/pe337.pdf . This is the range where they are the closest. Compare this range to WOT where your 250 Ox66 will burn something like 26 to 28 GPH while a DFI 2-stroke 250, such as the E-TEC, will burn between 22 and 23 GPH and at 1000 RPM where the Ox66 burns 3.8 GPH and the E-TEC just 0.74 GPH.
A few years ago here I noted a comparison of an 225 Ox66 versus an F225 4-stroke on a Pursuit 2470 walk around hull. The comparison indicated that the 225 Ox66 was as fuel efficient at cruise as the F225. The Ox66 was not efficient at near idle speeds as compared to the F225.
posted 11-19-2005 01:55 PM ET (US)
When comparing the conventional two-stoke engine at its most optimum fuel economy speeds (around 4,000-RPM) with any of the other types of engine, be it direct-injection two-stroke or any type of four-stroke, you will not find tremendous improvement in fuel economy. You should find about 30-percent improvement. I am quite surprised that a BRP spokesperson said you would not see any improvement between the E-TEC and a conventional port-injection two-stroke at 4,000-RPM.
There is a difference between port-injection and direct-injection two-stroke motors. The Yamaha Ox66 motor has port-injection. The fuel is introduced outside of the cylinder near the intake path or port. The E-TEC has direct injection, where the fuel is introduced directly into the cylinder.
At low engine speed it is very likely that all of the fuel injection in an E-TEC occurs during the time that the piston position has closed both intake and exhaust ports. This is why there is no unburned fuel in the exhaust. It may be that as the engine speed increases, fuel injection begins to overlap some of the port timing, leading to the potential for some unburned fuel. However, I do not think this occurs to any great degree. If it did, I doubt the engine would meet the emission levels needed. Remember that an engine rated for 2008 EPA compliance has reduced its emission to less than one-tenth of the previous engines (90-percent reduction).
For guidance I would rely more on the published specification for the E-TEC than the quoted comment of the representative at the boat show.
In recalling all the information I have seen on this topic, it looks to me like the E-TEC has a very substantial advantage at idle and trolling speeds, where improvements in fuel economy of three or four times are to be expected. The improvement tapers off as engine speed is increased. However, I would still expect the E-TEC to perform better than a port-injected two-stroke at 4,000-RPM.
The absolute best fuel economy at cruising speeds comes from relatively large displacement four-stroke engines with natural aspiration (no supercharging). These engines show better fuel economy than all other types. If you want to optimize fuel consumption at cruising, look at a 250-HP four-stroke like the Honda, Suzuki, or Yamaha.
posted 11-20-2005 11:45 PM ET (US)
This thread just made me realize that the E-Tec might be the best solution for a twin engine setup on my Outrage 18.
I've never considered using a high horsepower, carburated, 2-stroke outboard as a trolling engine because the fuel consumption below 600 rpm is so poor on my VRO 140HP V4 Evinrude circa 1988, not to mention the blue smoke coming off the back end of the boat. Bleah!
Peter, are you suggesting that the new Evinrude 90 HP E-Tec can troll all day at 400-600 rpm more efficiently than a Yamaha 150 4-stroke? If so, maybe I should install two E-Tec 75s or two E-Tec 90s.
The weight would be about 640 lbs versus 580 lbs for a Yamaha 150 HP 4-stroke and a 9.9 HP Yamaha kicker for my emergency power.
posted 11-20-2005 11:54 PM ET (US)
Or even use two of the 60 HP E-Tec engines - then the weight is down around 480 lbs.
I know Tony has said that his 115 HP Yamaha 4-stroke provides adequate power for light loads on his 18 Outrage but (60 x 2 =) 120 HP with the torque of a 2-stroke would probably be a good power solution.
I'd run both engines to get out to fish ( or to pull a water skier three times a summer ) and then shut one off to troll.
Wonder how a 60 HP engine would run an 18 Outrage in an emergency?
Sure a lot better than a 9.9 HP kicker!
posted 11-21-2005 12:39 AM ET (US)
With the right propeller pitch, I would bet that 60-HP would get an OUTRAGE 18 on plane.
posted 11-21-2005 01:04 AM ET (US)
Just to clarify my comments on port-injection versus direct-injection:
In a two stroke engine there generally is some overlap built into the port timing. The intake port and the exhaust port are both open at the same time. This is determined by the geometry of the cylinder walls and where the ports are located. But there is always some overlap. Therefore a two-stroke engine with carburetors or with port-injection will tend to have some fuel lost via the exhaust port before it is ignited. The air coming into the cylinder is already mixed with fuel. As this fresh air charge pushes out the combustion gases from the previous cycle, some of the air contains fuel and that goes out the exhaust, too.
On a direct-injection two-stroke, the fuel is sprayed into the cylinder after the ports have both closed. This is where the big savings on fuel is obtained in the low engine speed operation.
I don't think you can manage the fuel injection timing with port-injectors in such a way to avoid some loss out the exhaust port.
posted 11-21-2005 08:32 AM ET (US)
Roarque -- According to Evinrude's performance reports, a pair of 90 E-TEC's at 1000 RPM would burn between 0.6 to 0.8 GPH (0.3 to 0.4 GPH each). According to one peformance report, a 90 E-TEC burns just 0.18 GPH at 700 RPM. A single F150 burns between 0.6 and 0.8 GPH at 1000 RPM according to Yamaha. Interestingly, a single Yamaha F90 burns about 0.5 to 0.6 GPH at 1000 RPM. Yamaha doesn't show any consumption rates below 1000 RPM. So I think the data published by the two manufacturers suggest that two 90 E-TECs could be more efficient for trolling than a single F150.
As a practical matter, most likely you would be trolling faster with the pair of 90 E-TECs at 1000 RPM than you would be with a single F150. You could probably troll slower at 1000 RPM with only one of two 90s operating and have half the fuel consumption of the F150. However, we're talking about rates of consumption that are so low that I think the fuel consumption differences are mostly insignificant as a practical matter and shouldn't be the primary driver of a purchase decision.
Some might argue that the efficiency comparison doesn't take into account the 2-stroke oil consumption. The reality of it is that the lubrication costs between a modern DFI 2-stroke and a 4-stroke are really a wash so one doesn't really need to take that into account. I think the advantage actually tips in the favor of a DFI 2-stroke in that it continually gets fresh oil during those extended trolling times whereas with the 4-stroke there is a risk of oil contamination from fuel and water accumulating in the oil because the motors run so cool.
Interestingly, my pair of FICHT 225s combined consume less fuel at low engine speeds than your single 140. I think the fuel consumption difference between the stratified charged DFI 2-strokes, such as the E-TEC, FICHT and OPTIMAX (HPDI doesn't use a stratified charging mode and therefore has poor low speed fuel consumption), and the 4-strokes is caused by the need to burn more fuel to drive the valve train componentry.
Another option for you to consider is the E-TEC 150 coupled with the 9.9 kicker. That combination will weigh at least 50 lbs less than the F150 and 9.9 kicker combination, probably 100 to 125 lbs less than a pair of 90 E-TECs and about the same as a pair of 60 E-TECs.
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