Gas Consumption of older 2 vs 4 stroke engines???

[duganderson]

Hello,

I'm in the process of buying a used 19 to 22 ft. deck boat with an outboard in the 115--150 HP range for MN lakes. (the boats range in dry weight without motor from about 1500 lbs to 2300 lbs). My budget allows me to buy something in the 1997-2002 range.

Can you please help me get a sense of the gas consumption of these type of outboards with a 2 stroke vs. 4 stroke? (I would not be able to afford a boat with the new, direct fuel injection 2 strokes like the ETEC motors so I would be looking at the older type of 2 stroke engine.)

Can anyone give me a approximate sense of how many Gallons per Hour I would burn with a two vs. 4 stroke engine in......

--closed throttle or trolling speed
--water skiing at 32 mph with 4-5 people in the boat
--slow cruise with 8 people in the boat

If you know of any good resources that help me please let me know too.

Thank you VERY much.

 

[coolguy147]

Re: Gas Consumption of older 2 vs 4 stroke engines???

i would get the biggest engine that your boat is rated for.

in that year range 2 and 4 are about the same but the 2s i believe are relatively lighter and more abundant.

personally, i'd go with a 2 stroke seeing as you'll be boating with heavy loads as the 2 will be faster out of the hole.

 

[Silvertip]

Re: Gas Consumption of older 2 vs 4 stroke engines???

Fuel consumption is a rather difficult number to pin down in the categories you are interested in. For example slow cruising may be idle speed, it may be just on plane. As for water skiing at 32 MPH, that also is hard to pin down because of the boat, the size the people being towed and the load in the boat. Unless someone has plotted fuel curves for your exact boat, with a constant load, on the same day, and at various speeds from idle to wide open throttle you can only guess at the numbers and they will vary widely. One number you can count on is that at wide open throttle any engine (2 or 4 stroke) will burn about 10% of its rated HP per hour. Therefore a 115 at WOT will burn about 11.5 gallons/hour regardless what you are doing. Any throttle setting less than that is way to variable to predict. If you don't believe those numbers, go to the Yamaha web site and look at Performance Bulletins. Compare two and four stroke engines on the same boat (or reasonably close one). You will find the numbers very close. What you need to understand when reading those charts is that at any given RPM you will see the four stroke burns less fuel. But look at the boat speed at that rpm. In most cases the two stroke will be pushing the boat faster at the same RPM so understand what you are looking at.

 

[JB]

Re: Gas Consumption of older 2 vs 4 stroke engines???

My 2001 Suzi DF70 used about half as much fuel as the 1980 'Rude 100 it replaced.

 

[dingbat]

Re: Gas Consumption of older 2 vs 4 stroke engines???

Most switching from carbureted 2 stokes to 4 strokes are seeing a 30-40% reduction in fuel usage.

http://www.outboard-motors-and-boating-geraldton.com/support-files/fuel-efficiency.pdf

 

[Silvertip]

Re: Gas Consumption of older 2 vs 4 stroke engines???

Most switching from carbureted 2 stokes to 4 strokes are seeing a 30-40% reduction in fuel usage.

http://www.outboard-motors-and-boating-geraldton.com/support-files/fuel-efficiency.pdf

Not at wide open throttle. Again -- I refer folks to the Yamaha web site. That is about the best source of performance comparison data available by any manufacturer. I also have run 2 stroke and 4-stroke motors and while the four strokes tend to do better at mid range and idle, the fuel consumption curves get very close together as rpm goes up. 30-40% reduction is huge and unless I see the actual numbers (rather than gas gauge guesswork) I don't buy it. In a study that I did some time ago, a 70 HP Yamaha 2-stroke actually got slightly better economy than a 75 4-stroke on the same boat. Yes - 5 HP difference but definitely not 30 - 40%. I will admit I do not follow the 150 & up engine sizes because they are of no interest to me so perhaps there is a wider spread in that category. And there were some gas hogs back in the day so one cannot base economy data on one specific series or year of engine. Lastly -- there is a balance of economy and performance just like there is in a car or truck. You can set up an engine so it sips fuel but is a slug for performance. Or you can have it perform like beast and burn fuel like there is a big hole in the tank. Therefore compromise is what most manufacturers strive for since fuel is no longer 75 cents a gallon like it was in the good old days. To prove my point (using Yamaha numbers) here are two test reports on an Alumacraft 175 (2500 - 2700# as tested) with a 2-stroke 150 and a 4-stroke 150.
Most notable is that at ANY rpm the two stroke is ALWAYS pushing the boat faster than the four stroke. In fact the four stroke won't even get on-plane until 3000 RPM whereas the two stroke does so at somewhere between 2000 and 2500. At 2000 RPM the 2-stroke is at 11.1 MPH and 4-stroke is at 7.6 mph. Going back to idle the 4-stroke sips fuel at 7.83 MPG (0.6 gph) while the 2-stroke uses it at 1.4 GPH (3.93 MPG). Guess what happens at 3000 RPM? The 2-stroke is now 5.5 MPH faster and MPG is 5.45 (2S) and 5.58 (4S). From this rpm to WOT the 2S ranges from 6 - 9 MPH faster and at WOT throttle -- guess what. The 2S MPG is at 3.67 and the 4S is at 3.29 so again -- where is this 30 - 40% better???. At WOT the 2S is buring fuel at a rate of 13.7 GPH and 4S is at 14.6. Both of those numbers are pretty close to 10% of 150 HP are they not??? Again - when comparing data like this make sure you understand what you are comparing. If you look strictly at RPM - then a 4S is almost always using less fuel. DUH -- it is also pushing the boat much slower than the 2S at the same rpm. So compare speeds (which relates to distance traveled) and you will see that 40 MPH (39.3 on the 2S) the fuel burn is 9 GPH and 4.37 MPG. On the 4S at the same speed the engine must rev to almost 5000 RPM and the burn rate is 10.9 GPH or 3.8 MPG. These are Yamaha numbers folks -- not mine.

 

[freetime99]

Re: Gas Consumption of older 2 vs 4 stroke engines???

I believe that where the efficiency of the 4 stroke is showing up is at idle and slow forward speeds, where fuel is used a lot more efficiently by the 4 stoke design. A lot of time is spent at those speeds. The carbed 2 strokes tend to not burn fuel in an effective manner at slow speeds. I agree with the previous reply, at full speed, the 2 strokes report well.

 

[dingbat]

Re: Gas Consumption of older 2 vs 4 stroke engines???

I will admit I do not follow the 150 & up engine sizes because they are of no interest to me so perhaps there is a wider spread in that category.

In my world, a 150 HP motor is small. You don't see much smaller than 200 HP unless run in pairs.

Most of our boating is done at cruise speed. You leave the inlet, set the throttles at cruise (4000-4500 RPM) and run 35-60 miles to the fishing grounds. Troll for 6-8 hours, and then run back in. Using WOT fuel consumption for comparison has no basis in realtiy when you can count the number of times run WOT in a season on your hands and feet.

Here are real world actual numbers:

Grady White 226 with 200HP Evinrude Ocean Pro -carbureted 2-stroke.

At 4000 RPM, 29.5 MPH, 13.59 GPH, 2.17 MPG per Garmin GFS-10 fuel flow sensor.

The advertised numbers for a Yamaha F200 on my boat at 4500 RPM is 32.2 MPH, 9.8 GPH, 3.3 MPG
http://www.gradywhite.com/228/performance_data/1/F200

The advertised numbers for a Yamaha F250 on my boat at 4500 RPM is 33.2 MPH, 12.8 GPH. 2.59 MPG
http://www.gradywhite.com/226/performance_data/1/F250

Even if I put 250HP 4-stroke on the back, my fuel consumption would still drop by 17%. If you compare apples to apples, 200HP to 200HP you?re looking at 38% decrease in fuel consumption when going from a 2 stroke carb to a 4 stroke. I know a couple of guys running 225HP Hondas that are getting even better numbers than the Yammi F225.

Go over to THT or any other board with people who do a lot of coastal boating. They will tell you to the same thing. Expect to save 30-40% in fuel costs when going from a 2 stroke carb to a 4 stroke.

 

[Bamaman1]

Re: Gas Consumption of older 2 vs 4 stroke engines???

You've received good information above. Another good place to look for relative boat performance is BoatTest.com.

I'm running a 115 hp Yamaha two stroke on a 24' pontoon boat, and get a respectable 4.5 mpg at a normal 3000 rpm cruise. Much smaller engines at the same speed won't get better mileage, as they'd be running flat out @ 5000+ rpms.

My boat accelerates like a bass boat coming out of the hole--until it suddenly hits a speed wall @ 20-22 mph. Pontoons are like that.

My thoughts are to go with a 2 stroke if you are heavy on the throttle--pulling skiers/tubers or if you're a fast cruiser.

If you carry heavy loads (people) and cruise a little above where you plane off--go with the 4 stroke. My neighbor has a 150 Suzuki on a 19' deck boat, and he says it is very fast on top end.

I will be going with a 150 hp 4 stroke on my next pontoon boat--max. for the hull. I like having too many horses vs. not enough horses. Remember that fuel is just a small part of your boating expense.