Fuel economy

[jerryjerry05]

On another site a guy posted about fuel usage and economy.
He said that the EFI was no better on fuel than the carbed models.
Any comments???

Thanks,J

 

[WrenchHead]

After thinking about your question I would guess if both systems were in perfect order then any difference might be hard to measure. Tthe cylinder/piston responds best to a correct air/fuel ratio no matter how it is delivered to the cylinder. If that ratio is not perfect it will effect the gasoline economy. Is it possible that the EFI is more accurate over time? But like a carb, the injectors must be clean. You could probably argue the issue all day yet never be able to perform an accurate test to prove either case.

 

[Tnstratofam]

+1 to above. I believe an engine if properly tuned will perform equally whether carbureted or fuel injected. However change the drive assembly or gear ratio, and all bets are off. I owned a 1974 Datsun pickup with a 4cyl 4 speed carbureted and averaged 20 miles to the gallon. I own a 1988 Ford ranger 4cyl 5 speed fuel injected and average 20 miles to the gallon. Both trucks had similar weight, and gear ratios. The Ranger has one more gear yet it isn't noticeably better than the Datsun. Way too many variables for me to calculate.

 

[pckeen]

Take a look at this link - it has some side by side comparisons. http://www.boat-fuel-economy.com/mercury-mercruiser-3.0-181-fuel-consumption-liters

Similar displacement engines had higher horsepower in the fuel injected models, but were correspondingly higher on gas - so looks like overall, the fuel consumption on a new carburetted vs. fuel injected motor would be very similar.

 

[undone]

At WOT the usage can be close, at lower RPMs the fuel injected motors tend to do better, sometimes much better, plus they tend to start and run better.

 

[steelespike]

There is a very general rule of thumb that a marine engine will use fuel at at "ABOUT" 10% of the rated hp.
After a discussion regarding the rule of thumb and some research I found some limited tests for new carbed 2 strokes.
I did find 50 hp tests indeed they do use at least 11% and some more.The few smaller motors I found much higher 14% or more.
Older motors 1950s and1960s Are much higher I found a 1950s 12 hp that was officially rated at 2 gph.
I used Etec performance tests only because they are really complete and direct injected.
I averaged results using only aluminum boats to try to have as equal as possible from 25 to 60 hp.Boat size weight and design don't affect gph.
25 hp averaged 2.63 gph over 4 tests,the 30 hp averaged 2.33 over 3 tests,40 hp averaged 4.13 over 3 tests,the 50 hp 4.79 over 4 tests,
the 60 averaged 4.74 over 5 tests.
2 things I notice the direct injected motors are indeed well within the 10% rule of thumb.
The 25 is a choked down 30 and has a higher gph average. The 40 and 50 are choked down 60s the 40 can't quite make the 10% rule
and the 60 kicks the rules butt.

 

[robert graham]

Would the Yamaha Outboard Performance Bulletins be a good reference for comparisons?....

 

[tpenfield]

I don't think "fuel economy" in boats exists . . . there is nothing economical getting 2,3, or even 4 miles per gallon of fuel.

EFI engines are a bit nicer than Carbed engines, but if you are operating at a 2 mpg baseline it is hard to envision the savings.

 

[undone]

Would the Yamaha Outboard Performance Bulletins be a good reference for comparisons?....

It's a good place to start.

 

[Sea Rider]

Each brand engine wether being 2,4 stroke or Efi models has their own factory fuel consumption rates which manufactures should provide to customes to account if planning long cruises.

Can't use Yam's rates as a refference for all brand models. To each his own.. Some will render more or less MPH if comparing same HP between brands. Anyway, comparing car gas mileage to boats, all engines are real fuel thirsty guzzlers.

Happy Boating

 

[jerryjerry05]

Thanks all who responded.
I have twin 88/85's now.
I get on average 2.2-2.3 miles per gal.
The link PCKEEN posted I think was for new motors.
I guess I should have gave a bit more info.
Probably would have gotten a bit different feedback.
I'm changing to a single 200 or 225
I had a similar set up on a similar boat with a 225 EFI and the difference in gas usage was way better.
Thanks,again.J

 

[Chris1956]

I think the point missed was "what kind of EFI?" The vanilla kind of EFI is where a throttle body with an injector replaces the carb. Not much difference in economy will be had with this system. A better type of fuel injection is Direct Injection. Here gasoline is injected into the combustion chamber, after the ports (2 cycle motor) or valves (4 cycle motor) are closed. Fuel economy is greatly improved with this system in a 2 cycle motor, due to exhaust scavenging being done with fresh air, versus air/fuel mix. Fuel economy in a 4 cycle motor is improved a bit as well, over sequential manifold injection.

I do not currently know of any direct injection 4 cycle marine motors, but I expect to see them in a few years, as this technology is in the automotive industry today.

 

[undone]

Thanks all who responded.
I have twin 88/85's now.
I get on average 2.2-2.3 miles per gal.
The link PCKEEN posted I think was for new motors.
I guess I should have gave a bit more info.
Probably would have gotten a bit different feedback.
I'm changing to a single 200 or 225
I had a similar set up on a similar boat with a 225 EFI and the difference in gas usage was way better.
Thanks,again.J

Those 88 specials were very thirsty motors, you should see a huge difference in fuel efficiency by switching to a larger newer single motor no matter what it is.

 

[steelespike]

delete

 

[JustJason]

The actual first gen EFI engines are slightly better than carbureted engines. By slightly I mean 10% max. The newer DFI engines are 30% or better over carb'd engines.

If fuel economy is a huge concern think about how you boat, what speeds, and what activities you do. And pick the prop that is going to give you the least amount of slip for that activity. Efficiency/economy/slip are all related.

As for this

#4
Take a look at this link - it has some side by side comparisons. http://www.boat-fuel-economy.com/mer...umption-liters

Similar displacement engines had higher horsepower in the fuel injected models, but were correspondingly higher on gas - so looks like overall, the fuel consumption on a new carburetted vs. fuel injected motor would be very similar.

I can't imagine that website being very accurate. Diesel engines in the real world work on brake specific fuel consumption, where for all intents and purposes the amount of load does not matter, or effect, overall fuel economy. But gasoline engines do not work that way. On paper they do, but real world conditions change it to much for bsfc to be any kind of accurate. Simply speaking a 5.7 in a 21 foot boat is going to get much better economy than that same engine in a 27 foot boat, and I'm talking rpm to rpm, not speed.


1 thing that stands out though, if it's true, is that Mercs new 4.5 V6 gets worse fuel economy at 250 horsepower than a 5.0 does at 260 horsepower. Kinda makes a 5.0 a more attractive option. More power and better fuel economy.

 

[jerryjerry05]

Undone, your right about the 88 Specials being hogs.
I have 88/85hp Forces and they are better but not much.
I have a line on a 1999 Optimax 200.
They along with the HPDI(Yam) and the Evendude E-Tech al have the Direct Injection.
Luckily I have saved all the controls and dash panels from the last Mercury.

 

[undone]

Undone, your right about the 88 Specials being hogs.
I have 88/85hp Forces and they are better but not much.
I have a line on a 1999 Optimax 200.
They along with the HPDI(Yam) and the Evendude E-Tech al have the Direct Injection.
Luckily I have saved all the controls and dash panels from the last Mercury.

For some reason I thought you had the J/E 88 specials from 1985, not 1988 Force 85's. Maybe I should have read it a little closer. I had a 90hp Force, it was as bad as or worse than the J/E 90/88

 

[jerryjerry05]

If they're set up right and not ran wide open, they can be fairly good.
Like I said running twins and getting 2.3/2.3 miles per gal. Isn't bad not great but ok.
My neighbor had a 17 with the 88 and it blow a piston and he put a 110 on and it doubled almost tripled the usage???

 

[Dukedog]

Just a word of caution. First "opti's, till '01's, had problems. Probably VERY few with original power heads out there. Bright side thought. If is original and still running its one of tha good ones. Not original and running most problems have been addressed by Merc. Just get it checked by a trust worthy mech.....jmo

Opti/dfi/4 stroke only for fuel efficiency. Rest not enough difference ta mater..........

 

[pckeen]

[QUOTEThanks all who responded.
I have twin 88/85's now.
I get on average 2.2-2.3 miles per gal.
The link PCKEEN posted I think was for new motors.
I guess I should have gave a bit more info.
Probably would have gotten a bit different feedback.
I'm changing to a single 200 or 225
I had a similar set up on a similar boat with a 225 EFI and the difference in gas usage was way better.
Thanks,again.J][/QUOTE]

VERY different answers.

If you repower with a newer EFI engine you will notice a huge difference in fuel consumption. I went from a 115hp 70s Johnson to a nearly new 90hp Yamaha, and it uses about 1/4-1/3 of the fuel. Even with a 115hp, it would have been at least a 50% savings.