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115 vs 140 - help me do some math on fuel consumption

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115 vs 140 - help me do some math on fuel consumption

Old 03-23-2019, 08:09 AM
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Default 115 vs 140 - help me do some math on fuel consumption

Input appreciated. I'm trying to get my head around this.

I'm repowering a 22' panga type boat. It's a heavy import no-name model I built out for myself and love. It's running a 2005 Yamaha 90 2 stroke spinning a very low pitch prop. Though a bit more speed would be nice, performance is perfectly acceptable. But since I'm repowering, I'm figuring let's go ahead and step up to a 115 so we're not at the bottom of the acceptable range.

I'm shopping in the used market for a 115, and I'm shopping for the engine, not the brand. By that I mean the cleaner engine at the right price will win out over brand preference. Yamaha, Suzuki, E-tec, or Merc, the best option that comes along will get the nod. I'm open to running new controls, not an issue.

I'm assuming all 115's are similar enough in output and fuel economy in modern models (say 2014 or newer). A few pounds this way or that way or a hair better performance in any measure isn't really an issue for me.

I'm assuming any modern 115 is going to burn less fuel than my old 90 2 stroke, especially since that one is cruising at about 4600 rpm and something bigger is going to turn slower for the same speed.

The issue of fuel consumption is important because I have a small fuel tank on deck (22gal). I'm hoping to extend range with the repower, as I sometimes get home with just a few gallons to spare.

In shopping for a used 115 we find that a) there's not a lot of them on the market b) people selling used Yamahas are smoking a lot of crack and c) boy, those Suzuki 140's are nice and there's a few of them around in nice shape.

All that said, the questions are:

Is my assumption that I'll notice an improvement in fuel economy going to a modern 115 a good one?

Would going to the Suzuki 140 instead of a 115 eliminate my gains in fuel economy, or would it still be an improvement over the old 90?

Thanks for helping me figure this out. If you're wondering, going to a modern 90 is an option, I'd just like that little bit better speed with a 115 when it's calm in the backcountry and I have 10 miles to run, but not at the price of range. Range is consideration #1. It cannot go down at all, and we're trying to increase it as best we can.
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Old 03-23-2019, 11:14 AM
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Going to a 4 stroke will reduce fuel consumption.

Each engine manufacture has performance bulletins showing motor fuel consumption rates. I suggest that you dig into those so you have a better idea of the variations.

I definitely would go with the df140 if your boat is rated for the hp. It will consume more fuel than a 115 only at near full throttle.
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Old 03-23-2019, 03:00 PM
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Ran a panga 22 with yammie 115....5 mpg all day....it pushed it along easily up to where it got uncomfortable....30 mph....any chop at all and you are 17-22 mph....a 140 will not gain you anything....
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Old 03-23-2019, 03:07 PM
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at similar cruise speeds, the 115 and 140 will use similar amounts of fuel.
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Old 03-23-2019, 03:38 PM
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Very very big ballpark number. For OBs WOT is 10% of rated hp so the max for a 115hp is will be 11.5gph.
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Old 03-23-2019, 03:53 PM
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The Suzuki 115 and 140 are the same weight and cc capacity.

At the same cruise speed, their fuel economy will be so close to identical it will not be funny.

You will come close to using half the fuel with the Suzuki’s that you currently used with the 90 Yammy 2 stroke.
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Old 03-23-2019, 04:20 PM
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I agree the the cruise number would be the same for a given speed between the 115 and 140. But if your cruise speed if faster with the 140 then it will consume more fuel.
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Old 03-23-2019, 04:33 PM
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An educated guess is the best anyone can do here unless they've actually tested your hull with different engines. That being said a 115 4 stoke should definitely give you better fuel economy than a 90 2 stroke. A 140 4 stroke will burn more fuel at WOT than a 115, but if the 115 and 140 have the same displacement I would expect their fuel burns to be pretty close at a midrange cruising speed. Pangas are generally recognized as being able to cruise comfortably with smaller power plants than their V hulled brethren. I'd also expect a 140 4 stroke to burn less fuel than your 90 2 stroke if you run it at the same speed at which you ran the 90 - and probably still less cruising at speeds even higher than you ran the 90. I do believe you will find either size will put a smile on your face after you reposer.
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Old 03-23-2019, 04:37 PM
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Originally Posted by ndb8fxe View Post
I agree the the cruise number would be the same for a given speed between the 115 and 140. But if your cruise speed if faster with the 140 then it will consume more fuel.
Thank you all for the input.

Theres no going much faster in a panga unless it's flat calm. It's just that there's no weight penalty or fuel penalty between the 115 and Suzuki 140, so I may as well put them on the list of possible choices. That's what I wanted to clear. Thanks.
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Old 03-24-2019, 07:46 AM
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Originally Posted by VA12 View Post
Input appreciated. I'm trying to get my head around this.

I'm repowering a 22' panga type boat. It's a heavy import no-name model I built out for myself and love. It's running a 2005 Yamaha 90 2 stroke spinning a very low pitch prop. Though a bit more speed would be nice, performance is perfectly acceptable. But since I'm repowering, I'm figuring let's go ahead and step up to a 115 so we're not at the bottom of the acceptable range.

I'm shopping in the used market for a 115, and I'm shopping for the engine, not the brand. By that I mean the cleaner engine at the right price will win out over brand preference. Yamaha, Suzuki, E-tec, or Merc, the best option that comes along will get the nod. I'm open to running new controls, not an issue.

I'm assuming all 115's are similar enough in output and fuel economy in modern models (say 2014 or newer). A few pounds this way or that way or a hair better performance in any measure isn't really an issue for me.

I'm assuming any modern 115 is going to burn less fuel than my old 90 2 stroke, especially since that one is cruising at about 4600 rpm and something bigger is going to turn slower for the same speed.

The issue of fuel consumption is important because I have a small fuel tank on deck (22gal). I'm hoping to extend range with the repower, as I sometimes get home with just a few gallons to spare.

In shopping for a used 115 we find that a) there's not a lot of them on the market b) people selling used Yamahas are smoking a lot of crack and c) boy, those Suzuki 140's are nice and there's a few of them around in nice shape.

All that said, the questions are:

Is my assumption that I'll notice an improvement in fuel economy going to a modern 115 a good one?

Would going to the Suzuki 140 instead of a 115 eliminate my gains in fuel economy, or would it still be an improvement over the old 90?

Thanks for helping me figure this out. If you're wondering, going to a modern 90 is an option, I'd just like that little bit better speed with a 115 when it's calm in the backcountry and I have 10 miles to run, but not at the price of range. Range is consideration #1. It cannot go down at all, and we're trying to increase it as best we can.
I had a suzuki 115 on a 20 foot panga inspired Maratime 20p. Upgraded to a new suzuki 140. Its actually the same motor only the 140 wheighs 6 pounds less then the 115. I gained about 2mph and lost about 1mpg.
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Old 03-24-2019, 08:51 AM
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While I drive a sterndrive boat, I would go with the higher horsepower engine for its ability to get you on plane easier when the boat is loaded heavily. At partial throttle, I think you would find fuel economy similar between the two engines.
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Old 03-24-2019, 10:48 AM
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Originally Posted by barrell View Post
I had a suzuki 115 on a 20 foot panga inspired Maratime 20p. Upgraded to a new suzuki 140. Its actually the same motor only the 140 wheighs 6 pounds less then the 115. I gained about 2mph and lost about 1mpg.
I was thinking I might do the same but with twins. Was this 1 mpg at WOT or just an average. 1 mpg is a big number when you have a small fuel tank.
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