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

[jay_merrill]

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

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

That could be, I've just never seen any boat tests that show 6 mpg at a planing cruise speed, with a similar configuration. A few of them that I have looked at have shown much higher numbers than what I get, but at non-planing speeds. I would love to find a motor that would give me 6 or 7 mpg!

 

[triumphrick]

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

Or......you could compare these tests of the same boat with the different technologies.....I think the op was questioning the Yamaha 90..

http://www.yamaha-motor.com/assets/...tb_2StrokePerf_HPMidPort_90hp_02-50-PLK-A.pdf

http://www.yamaha-motor.com/assets/...kePerf_MidThrustJetPort_90hp_02-147-PLK-B.pdf

 

[Silvertip]

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

It always comes to this point anyway so I'll post this data. Here are Alumacraft tests on an Alumacraft Navigator Sport 175 powered by a Yammy 150 and the other by a 150 E-tec. The thing that should pop out immediately is the E-tec is not propped correctly as WOT is only 5300. It should be in 5500+ range so top end would be significantly higher. Even as is, the Etec is running 600 rpm slower than the Yammy at the same boat speed. A proper prop would also help the top end fuel flow. But look at the displacement speed and fuel flow -- the E-tec eats the 4-stroke. The 4-stroke has a sweet spot at 3500. But across the band the E-tec is 3+ mph faster. So -- I'm done here. You can draw your own conclusions and make the charts fit your needs. Remember -- these are Alumacraft numbers, not Yamaha, Evinrude, or mine. By the way, time to plane with Yammy was 3.9 seconds. Time to plane on the E-tec was 3 flat.

 

[mthieme]

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

Here's a test with a bigger heavier boat by Popular Mechanics giving 30-45% better economy.
www.popularmechanics.com/outdoors/boating/1276841.html?page=3

 

[seahorse5]

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

Here are Alumacraft tests on an Alumacraft Navigator Sport 175 powered by a Yammy 150 and the other by a 150 E-tec.

For a better comparison, don't worry about rpms as different gear ratios keep them from being the same, look at the speeds and the mpg at those speeds where they are almost the same.

Fuel economy is always measured at a certain speed, not an rpm.



--------Yamaha ---------------------- E-TEC

idle speed - N/A -------------- idle 2.5 mph - 14.1 mpg
4.6 mph - 5.8 mpg --------------- 5.0 mph - 11.1 mpg
7.6 mph - 2.2 mpg --------------7 mph - 6.2 mpg
33.3 mph - 4.8 mpg ------------- 33.2 mph - 5.8 mpg
38.4 mph - 4.5 mpg ------------ 38.3 mph - 5.4 mpg
43.5 mph - 4.1 mpg --------------43.7 mph - 5.2 mpg
48.3 mph - 3.5 mpg -------------48.2 mph - 3.8 mpg

 

[Silvertip]

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

Fuel economy is "not always" measured at a certain speed. The first column in every economy chart is always RPM. That translates to a given speed. If it were measured at a given speed that would be the first column. MPG is a "result" of a given set of circumstances (rpm, gear ratio, prop, hull, etc). That's why I tell people to look at the speed when looking at these charts. That does not mean however, that RPM is the key thing to look at for the reasons you point out. It is however the measurement point.

 

[QC]

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

All of the data matters, but seahorses point is 100% valid, despite the chart being built around RPM it is boat speed and MPG that ultimately matters to the guy paying the bills . . .

 

[triumphrick]

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

"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?"........ORIGINAL POST........MARK42.......


How the heck did this thread get into an "us vs. them" situation???

It seems that I posted from a Yamaha site that at least showed two different technologies for the same boat. Wasn't that the op's original question? Didn't he mention the Yamaha 90??

I could give a r*ts *ss what prop was on "your" motor.

If I wanted to see this cr*p, I would be over on the THT forum.

Why doesn't someone go find a test of the Mercury or Johnnyrudes in both 2 and 4 strokes on the same boat and post that way. This post has NOTHING to do with what motor brand is better than another...

 

[QC]

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

I agree Rick, the data you posted is an exact answer to Mark's original question. Appears to be Carbed 2 stroke vs. a 4 stroke. That would be "older" 2 stroke technology vs. a newer 4 stroke.

 

[jay_merrill]

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

I also don't think top end would be significantly higher if the engine had been propped to achieve 5,500 rpm instead of 5,300 rpm. To make the gain in rpm, the pitch would have been reduced by an inch, so you would have a prop that was spinning faster but "pushing less water."

While there are certainly many variables, my experience with prop pitch is that reducing pitch to obtain more rpm, does not make a boat go faster. Every time I have ever done it, the result has been less speed and higher fuel consumption. That is not to say that my experiences are all encompassing - I'm sure they are not. My point, however, is that there are many situations where the outcome is not good from a speed and/or economy perspective.

 

[mthieme]

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

While there are certainly many variables, my experience with prop pitch is that reducing pitch to obtain more rpm, does not make a boat go faster. Every time I have ever done it, the result has been less speed and higher fuel consumption. That is not to say that my experiences are all encompassing - I'm sure they are not. My point, however, is that there are many situations where the outcome is not good from a speed and/or economy perspective.

I have the same experience.
I agree...nobody has even touched load or hull design yet.

 

[Silvertip]

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

To increase speed AND RPM does not always take a prop with more pitch. It merely takes better setup or a different style of prop. In this example it might even have been water conditions that prevented a WOT run. We don't know that. Setup alone can make a world of difference in performance.

 

[Silvertip]

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

To increase speed AND RPM does not always take a prop with more pitch. It merely takes better setup or a different style of prop. In this example, it might even have been water conditions that prevented a WOT run. We don't know that. Setup alone can make a world of difference in performance. Engines that are lugging can suddenly come to life with a very small change of prop or setup. The resulting change in RPM directly affects speed.

 

[pvanv]

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

Fuel economy is "not always" measured at a certain speed. The first column in every economy chart is always RPM. That translates to a given speed. If it were measured at a given speed that would be the first column. MPG is a "result" of a given set of circumstances (rpm, gear ratio, prop, hull, etc). That's why I tell people to look at the speed when looking at these charts. That does not mean however, that RPM is the key thing to look at for the reasons you point out. It is however the measurement point.

ST is right on the mark. MPG is Miles/Gallon. Nothing more and nothing less. Yes, of course you can compute that by having MPH and gph, and cancelling out the hours. Forget trying to evaluate RPM, pitch, etc. Different motors (and different technologies) have different optimal running conditions. In order to do an apples-to-apples comparison, the setup must be optimized for that particular motor and speed, and the loads -- all loads (boat, current, wind, etc.) must be identical. Then do an actual consumption measurement -- both distance traveled and fuel consumed. For a real eye-opener, take a look at the Evinrude website (for example), and look at the tech data. MPG is awful at slow speeds (below plane for a planing hull, and below the efficiency range for a particular motor), and also drops off at WOT. There is a definite "sweet spot" for any given combination of boat and motor, where economy will be best. So MPG will vary dramatically depending on boat speed. The computations should be normalized (for the math types) so that the data doesn't mislead us.

 

[jay_merrill]

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

I haven't seen the Erude mpg data, but from other tests that I've seen, absolute best mpg is usually found at low displacement speeds. It then drops dramatically as the boat speeds up, but remains below planing speed. As plane is achieved, the mpg increases quite a bit and then drops once more, at a certain point where fuel consumption required for a faster speed, increases exponentially.

I think in just about any boat setup, the worst mpg is going to be found at speeds where a large bow wave is being pushed, prior to rising up on plane. The reason for this is pretty obvious - its takes a lot of power (fuel consumption) to push the bow wave, but the boat isn't going very fast.

I do agree that engine/prop setup can affect rpm and boat speed quite a bit, even when there is no pitch change. I went from a 15" pitch aluminum wheel on my motor, to a 15" pitch, cupped SS prop. I had never owned a SS wheel before and I thought I might lose rpm, but didn't. I actually bought the prop because the deal was too good to pass up ($50, recently back from prop shop & excellent condition), not because it was exactly what I was looking for. Strangely enough, I gained 150 rpm! Diameter is the same on both props and nothing else was done to the setup.

 

[QC]

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

absolute best mpg is usually found at low displacement speeds.

Absolutely 100% correct, and this illustrates how important hull efficiency is to this discussion. The fact is that low idle is the least efficient point for a throttled, spark ignited engine, yet the most efficient for almost all boats powered by them . . .

 

[jevery]

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

Sorry to regress here, but

Remember -- these are Alumacraft numbers, not Yamaha, Evinrude, or mine. By the way, time to plane with Yammy was 3.9 seconds. Time to plane on the E-tec was 3 flat.

To be accurate, these are not Alumacraft tests. They are Yamaha and Evinrude tests that Alumacraft has linked to, and in the literally hundreds of these reports that I?ve compared these two are the most extreme example favoring the E-TECS that I?ve run across. Not typical.

http://www.yamaha-motor.com/assets/...thrustjetport_rel_alm-nav175sport-f150txr.pdf
http://www.evinrude.com/NR/rdonlyres/7A182705-0827-4180-8715-D6161773608C/0/PE511.pdf

These are true third party tests comparing E-TECS to the current state of the art, (IMO), four strokes.

http://www.proliteboats.com/index.html

IF we?re comparing fuel efficiency of E-TEC's to EFI four-strokes at like speeds,

http://i539.photobucket.com/albums/ff354/21weber42/E-TEC/E-TEC-Suzuki.jpg?t=1234570489

If we?re addressing the OP?s question, I believe triumphrick covered that above.

 

[QC]

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

Not to be argumentative, but I find the Prolite data unusable due to the various (and unexplained) test weights . . .

 

[jevery]

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

Dang, now we?ve opened another can of worms. If the consensus is that the data is invalid then there is extremely little valid data available to compare outboards. As the vast majority of manufacturer?s performance reports only report published dry hull weight, published dry motor weight, plus appx load, (but not actual weight totals), these too will be subject to significant weight differences, and thus invalid for comparisons. I am only aware of a few instances of testing multiple platforms simultaneously with weights added to equalize weights to only motor weight differences. Of the six direct comparisons made by Pro-Lite, three have notable weight differences, though in only one test, the 22CC, is the difference significant and not in Evinrude?s favor

 

[QC]

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

I am fascinated by this stuff, so I seek solid answers with little conjecture and particularly avoid assumptions based on possibly outdated beliefs . . . the points you note above are why I like lots and lots of data. Even that can be wildly inaccurate, but at least you can see some trends developing. Any data is better than none, but the best tests are literally those performed on the same hull, with an engine swap and similar ambient conditions. Definitely hard to find.