Is the 4 cycle fuel conomy better than the 2 cycle?

[Mark42]

I'm always checking on the prices of used outboards. I'm wondering if the fuel economy of a newer 4 cycle is better than the older 2 cycle it repaced. Like the 90 hp Yamaha. The 4 cycle is about 100lbs heaver than the 2cycle, but if it gets significantly better economy, the weight issue could be overlooked.

What do you think?

 

[Silvertip]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Here's the deal with outboard fuel economy. 1) At wide open throttle it doesn't matter whether you have a two stroke or a four stroke for the simple reason it takes so much fuel to make so much horsepower. A 75 HP outboard will burn approximately 7.5 gallons/hour at WOT. 2) If you look at fuel economy charts, you will see the four stroke at any given RPM will produce a MPG (miles per gallon) figure that is better than a two stroke at the same RPM. BUT -- if you look carefully at those charts you will see that a two stroke generally pushes a boat faster at any given RPM than the four stroke. So what you say! Take this into consideration -- if you only have to run the two stroke at 3500 RPM to maintain XX MPH vs 4000 RPM to maintain that same speed, you will see the fuel economy between the two is nearly identical. Since you mentioned Yamaha, go to the Yamaha web site and look at performance tests. Compare a two stroke to a four stroke on the same boat and you will see this. In fact I once looked at the 70 Yammy two stroke and the 75 Yammy four-stroke on a particular walleye boat (don't remember which one) but the two-stroke actually got significantly better economy. Although it did give up 5 HP, it still performed better. As for very old two strokes vs new four strokes there would likely be some rather significant differences in economy. Unfortunately there aren't many charts around for old motors to use when making comparisons.

 

[mthieme]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Neighbor has a new 150 Yammy 4 stroke on a 20' Mako.
1.9 gph average mixed running.

 

[JB]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

From worst to best:

Carbed 2 stroke.
Carbed 4 stroke.
DFI 2 strokes and EFI 4 strokes are best and about the same.
DFI 4 strokes, if they ever get sold, will be better than the rest.

FYI, the better the fuel efficiency the cleaner they run.

 

[Mark42]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

That is surprising. I would have thought that the 4 cycle would have better fuel economy becasue it doesn't have the inefficient design of trying to empty and fill the cylinder at the same time. Either some fuel is lost out the exhaust, or some exhaust stays behind, but it never has as clean a discharge of spent gasses like a 4 cycle has. At least that is my understanding of poor 2 cycle economy.

 

[JB]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

That is true of carbed engines, Mark. The 4s is quite a bit more efficient than the 2s.

The reason the DFI 2 strokes are competitive with the EFI 4strokes is because they don't scavenge the fuel, they only scavenge the air. The fuel is directly injected into the cylinder with exquisite timing.

When (if) the DFI 4 strokes come along they will regain their advantage.

 

[Mark42]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Thanks for clarifying that JB. In my younger years I worked in small engine repair shops doing lawnmower and tractor repairs to pay for college. More often than not, the 2 cycle machines were running poorly due to fuel/oil/sludge buildup in the exhaust ports and muffler choking the motor. LawnBoy seemed to be a major offender in this area. I always attributed the buildup to overly rich running and excessive fuel/oil being pumped into the exhaust ports where the oil would coke up and block the ports.

Motors that had oil injection, like my '69 Yamaha enduro bike, never experienced this problem. I think because the oil was metered more precisely. Or maybe it was just because the motorcycles were better designed than the lawn mower and chain saws of that time.

 

[Silvertip]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

mthieme -- 1.9 GPH on a 20 foot Mako with a 150 Yammy???? I think you slipped a decimal point. 15 GPH (or possibly 1.9 MPG) is more like it at wide open throttle. 1.9 GPH on average is not even close unless all the boat does is idle. Check the Performance Bulletins on the Yammy web site.

 

[dingbat]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Something wrong.

I have a friend who has a 20' Grady Tournament with a Yami 150. Uses right around 6 gph at 4000 rpm cruise which yields roughly 26 miles per hour.

 

[pvanv]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Silvertip is right on the mark. The old premix carb 2-strokes were thirsty. My 74 'Rude 15 burned in excess of 2 gph when running more than 3/4 throttle, pushing my heavy sailboat. My new 9.8 4-stroke Nissan has yet to use 1 gph, even approaching WOT in the same application.

Figure about 10% of the hp at WOT for fuel consumption (in gph) on any of the current models as a rough starting point. (10 hp uses about 1 gph). So then the rate of consumption dictates both range (on a given tank) and cost per hour. Of course that 2-stroke oil also has a cost per hour... and, if comparing dollars per hour, don't forget that the old 2-smokes also went through plugs faster.

 

[mthieme]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

mthieme -- 1.9 GPH on a 20 foot Mako with a 150 Yammy???? I think you slipped a decimal point. 15 GPH (or possibly 1.9 MPG) is more like it at wide open throttle. 1.9 GPH on average is not even close unless all the boat does is idle. Check the Performance Bulletins on the Yammy web site.

I thought the numbers sounded light too.
I doubled checked with him earlier today. He's kept a log since new.
He said 1.5 gph average. He does not run WOT, motor has never seen over 3/4 throttle. Typical running is just enough to keep her on plane, maybe a couple hundred more.
Still sounds light to me, but then I don't see him filling the tank a whole lot either. Comparing it to my 'Ray with a 170hp 4.3, I run similarly and burn an average of 3 gph.
If I had a 4 cylinder 4 stroke 150 that burned 15 gph, it would be at the bottom of the channel.

 

[Silvertip]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Unless he has a fuel flow monitor and is using it correctly, I would ask how he able to determine GPH fuel flow. Using the gallons added and readings from an hour meter would work but would not be very accurate since most hour meters run whether the engine is running or not -- but the key does have to be in the RUN position. If he doesn't have a fuel flow monitor OR and hour meter, I think I would enjoy a discussion in a bar with some adult beverages involved in a friendly wager. Below are three fuel use charts (two for a 150 and one for a 115). You will note that none of the three engines comes close to 1.9 GPH on plane which for all three boats is about 3000 RPM. Also note that at WOT all three engines burn roughtly 10% of their rated HP in GPH. These are Yamaha numbers on three different boats (all center consoles) in the 19-20 foot range.

 

[QC]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

I agree with most of this, but while a 2 cycle has a couple of issues as far as efficiency is concerned you cannnot discount that it fires every time around. It costs fuel to turn a cylinder once when it contributes nothing, so the 2 cycle earns some of the losses back . . . Also, while static fuel efficiency numbers usually show a 4 cycle as being more efficient as far as fuel burned for hp created is concerned, the weight benefit does improve in-use fuel efficiency enough to often even out the slight edge the 4 cycle offers.

Mark's first question was newer 4 cycle vs. older 2 cycle . . . that combo should siginificantly favor the 4 cycle, even with the 100 lb. penalty.

 

[reelfishin]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

I think if I were contemplating a motor swap, with the options being an older style 2 stroke vs. a modern 4 stroke, I'd have to seriously consider whether that added weight would affect the boats capacity and free board enough to change the way I use the boat.

I have run only Yamaha 4 strokes when it comes to later motors and while they are cleaner, quieter and probably more efficient, the weight gain and cost of a new motor would be what put me off. I can buy a lot of gas for what they want for a new 4 stroke, and I guarantee my boat will run just as good or better without the added weight with my old motor. There's a lot of good older motors still available. Unless good used 4 strokes start popping up cheap, I'll stick with what's worked for me for years.

I also run all older boats, something just don't look right about a new 4 stroke on the back of a 40 year old boat, Especially if it's got a Japanese name on the side. (I wouldn't put a Yamaha or Nissan motor in my Ford, why would I want it in my boat).

There's a lot to be said for matching the proper weight motor to a boat, as much or sometimes more so than just horsepower. I find that I often am better off with say a 75 hp three cylinder vs an 85 hp 4 cylinder, or a 140hp V4 vs a 150hp V6. The few hp gained just don't make up for the added weight.
I had a Renken that was rated at 150hp, I hung an early 90's 150 on it. That motor replaced a mid 80's 140 hp which I needed for another boat. Both motors were in excellent condition. The 150 would push the boat a bit faster but had trouble getting the boat on plane with three guys, while the 140 didn't seem to be affected. The fuel consumption increased, and the boat sat too far in the water when anchored for my liking.
That was with a 2 stroke 150 hp, what would I have had if I had hung a 150 hp 4 stroke? I'd have most likely been sitting there with water coming over the splashwell in all but the calmest seas.

I Eventually went back to the 140hp, with the 150hp motor I found myself not using that boat as much since it was no longer a comfortable boat to use.
I would also think that the same thing applies with 4 stroke motors, the highest HP in a given motor family or weight is usually the best choice. If that HP is over what your hull can take, I'd go with the highest HP in the next lighter or smaller engine family.

 

[jay_merrill]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

My guess is that they guy who thnks he is getting 1.9 gph with his Mako, is really getiing 1.9 mpg. Such a figure would be right about what I would expect for his setup.

I have a 1972 Johnson 65hp motor on the boat that I am now using. As many of you know, this motor is a carbeureted, 3 cylinder, 2 stroke engine. Oil introduction is via premix at 50:1.

The boat is rated for up to 130hp, so I am underpowered by most people's standards. I also have the motor propped to achieve 5,100 rpm at WOT. At WOT, I make about 28 mph (GPS) on relatively flat water. My motor's "sweet spot" for fuel efficiency, seems to be at about 3,800 to 4,200 rpm. I typically cruise at 4,000 rpm. making about 22 mph. I don't do anything special to the motor to maintain efficiency, other than to use BRP Engine Tuner (similar to Seafoam) about once a year.

I'm always curious about how I am doing on fuel, so I often check my mileage. Using the distance ruler in Google Earth, I plot the distance traveled on each outing as closely as I can. That distance is then compared to the gallons used to refill my tanks, in order to obtain an mpg figure. As near as I can tell, without getting really crazy about logging the results of these efforts, I seem to average about 3mpg.

My guess is that my consumption would improve to about 4 mpg, if I were to buy a 75hp ETEC. I wouldn't buy a 4 stroke because I don't like them on relatively small boats. To me, they are too heavy and too expensive to maintain.

So, if I bought the ETEC, how much better off would I be? Not much in my estimation. My motor still has exceptional compression readings, and shows no sign of "going south" any time soon. Given my use patterns, I probably would save a couple of gallons per trip, if I went to an ETEC. On average, that might equate to about 4 to 5 gallons per week, so even at $4.00 per gallon, I might save about $20.00 per week in fuel costs. I would also save on oil costs with the ETEC, but I'm not up for trying to figure out the savings there. Just for the sake of discussion, however, lets say that I would save $1,040 per year in fuel and $200 in oil, for a total of $1,240.

Considering that an ETEC 75hp motor would probably cost me about $8,500 with a new control unit, installation and taxes, it would take nearly 7 years to "pay for" the ETEC under this comparison. If I were to factor in maintenance cost, I'm sure the number would be more like 8+ years. I'll leave that out though, to account for the probability of higher fuel prices.

Simply put, I like the numbers for my current setup just fine. I also have very little faith in any of the new, and very complicated motors, lasting 7 to 8 years. On the other hand, my Johnson is now 37 years old and going strong. It starts every time and takes me out into the boonies and back very faithfully. All of this being the case, I doubt I will buy a new motor, unless I just decide that the environmental concerns override the cost issues.

 

[Silvertip]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

I think the point that's being missed in this discussion is what I pointed out earlier regarding engine rpm as it relates to boat speed. Because 4-strokes generally a little doggy out of the hole, they are either geared lower or they are fitted with props having less pitch. The net result of this that on the same boat, a DFI 2-stroke will generally be pushing the boat anywhere from 2 - 5 MPH (in some cases more) that the same HP 4-stroke. So when you look at fuel use numbers, do not compare GPH at the same RPM -- you need to compare the consumption at the same speed. Because the DFI 2-stroke is running fewer RPM than the 4-stroke at that speed, the GPH numbers will be very close. If you do compare numbers at a given RPM you need to consider that the 2-stroke will get you to your destination quicker so the engine doesn't need to run as long to get there as the 4-stroke. Again, numbers can be confusing -- you need to understand what you are looking at and comparing. The manufacturers are out to confuse you!!!!

 

[QC]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Funny, Silvertip, but what you are ultimately recommending is comparing MPG . . .

 

[dingbat]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

The boat is rated for up to 130hp, so I am underpowered by most people's standards. I also have the motor propped to achieve 5,100 rpm at WOT. At WOT, I make about 28 mph (GPS) on relatively flat water. My motor's "sweet spot" for fuel efficiency, seems to be at about 3,800 to 4,200 rpm. I typically cruise at 4,000 rpm. making about 22 mph. I don't do anything special to the motor to maintain efficiency, other than to use BRP Engine Tuner (similar to Seafoam) about once a year.

I'm always curious about how I am doing on fuel, so I often check my mileage. Using the distance ruler in Google Earth, I plot the distance traveled on each outing as closely as I can. That distance is then compared to the gallons used to refill my tanks, in order to obtain an mpg figure. As near as I can tell, without getting really crazy about logging the results of these efforts, I seem to average about 3mpg.

My guess is that my consumption would improve to about 4 mpg, if I were to buy a 75hp ETEC. I wouldn't buy a 4 stroke because I don't like them on relatively small boats. To me, they are too heavy and too expensive to maintain.

I would say your seriously under estimated the fuel savings with the new fangled motors.

A guy I know runs a 27' Judge with a 225Hp Honda on the back. We cruises @4400 RPM, 28 MPH, 9.6 gallons per hour. That works out to 2.9 MPG. The motor only has 40 hours on it so I expect he'll see better once it's broke in. He is getting roughly the same MPG out of a 225Hp pushing a 27' cabin boat as you're getting out of a vintage 65HP pushing a much smaller boat.

I'm guessing you would have cut your fuel usage in 1/2. Probably still not enough to offset the cost of fuel alone. Figure in the resale value and you might be closer than you think.

As for complicated machines, if you bet the farm on which car would make it to 200K miles the day you drove it off the show room floor, which would you choose? A new 1967 Impala or a new 2005 Honda Accord? I've had both. Pretty easy choice for me.

 

[bman1bpm]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

I'll give a simple answer:

If you're upgrading from an older 2 cycle to a newer 4 cycle strictly to save money on fuel, you're gonna have to own that motor a longggggggggggg time to make up the money you spend on the new motor.

If you're running a 70's 2 stroke like me, then the fuel economy will definitely be better.
The evinrude ETEC motors are easy on fuel and have don't have the added weight of a 4 stroke.

The one thing we can all agree on is that a newer motor will be significantly better for the enviroment

 

[Silvertip]

Re: Is the 4 cycle fuel conomy better than the 2 cycle?

Certainly -- but a DFI two stroke running slower at any given speed will deliver the same or very nearly the same MPG as a four stroke that has to run faster at the same speed. I like to use my Impala as an example of how MPG can be a rather worthless number in discussions like this. I can easily get 35 MPG at highway speeds with that car. Impressive huh! Unfortuately, I've failed to define "highway speed" which in this case is 55 - 60 MPH which is legal in most of the USA. At 70 - 75 that number drops to 30 - 31. If you don't care how fast you are getting to your destination and MPG is a critical factor in your definition of economy, then by all means buy a four-stroke. But making flat statements that a four-stroke is more economical than a DFI two stroke is simply inaccurate since illogical comparisons are being made.

Unfortunely, people don't read these charts in an objective fashion and say look, the four stroke burns less fuel at wide open throttle. But at wide open throttle it is generally pushing the boat slower. Slow the DFI down to the same speed and MPG gets very close to the same or better than the four stroke. Numbers are just that -- the more data you provide the more confused folks become and when confused, all sorts of misinformation surfaces. Like the "Stimulus Package". I'm not biased -- I have both. Merc and Johson 2-strokes and a Suzy 4-stroke. 4-stroke works fine on the pontoon. I prefer two-stroke on my planing hulls.