Optimax 115 / 135 fuel consumption

[imported_stinger]

Hi to all,
can somebody tell me how much is the hour fuel consumption of the in subject engines. And oil?
thanks

 

[Silvertip]

Re: Optimax 115 / 135 fuel consumption

Put a decimal point one position left in the horsepower rating of any engine and it will indicate the fuel flow rate at wide open throttle. 115 = 11.5 g/hr, 135 = 13.5 g/hr. This is a rough figure and is affected by boat type, prop selection, water conditions, load, etc. It gets you in the ballpark. Obviously any engine will burn less fuel at lower throttle settings.

 

[imported_stinger]

Re: Optimax 115 / 135 fuel consumption

Hi,
but the advertisements says "fuel consumption is 40% less than others two stroke engines with carbs", I would like to know if someboby experienced that
bye

 

[Silvertip]

Re: Optimax 115 / 135 fuel consumption

Ahhh -- the good old advertising hype. Just like politics they only tell you half the story.. It's really quite simple -- an engine requires so much fuel to make so much horsepower and that maximum comes at wide open throttle. It doesn't matter one bit if its carbed, fuel injected, two-stroke or four-stroke. Where the economy enters the picture is anything less than wide open throttle. That is were the injected (two and four stroke) engines have the advantage over the carbureted two strokes. Don't believe me? Go to the Yamaha web site (Performance Tests) and compare their two stroke and four stroke engine fuel consumption at WOT on any boat. They are very close. You can also go to the I/O forum and check a post that the title of which is "wont idle for more than a few minutes". The engine being discussed is 502 cubic inch Chevy power plant that happens to be fuel injected. It's horsepower rating is into the 300 range and he says fuel consumption at WOT is 37 GPH. My 75 HP Merc flows 7.5 gallons per hour at WOT and that's measured with a fuel flow montor. There you have three examples of how close that technique really gets. Obviously the type of boat, the setup, the load, etc all affect fuel consumption so one must make sure an apples to apples comparison is made.

 

[butlp]

Re: Optimax 115 / 135 fuel consumption

Stinger,
I can't give you the exact fuel consumption for the 115, but my 2005 on a 16.5 ft runabout uses a lot less fuel and oil (approx 30% less) of my old 16ft with 90 hp yamaha carbed. Starting is a breeze, very quite and very little to no smoke or 2 stroke smell. Getting the prop pitch right has been my only issue but I think I now have that sorted.
So far wit approx 75 hours it has run flawlessly and I'm very pleased with this motor.
I also have a 2003 50 Merc EFI four stroke on my pontoon and it has run flawlessly, however it's not as quite as the optimax and you can smell the exhaust with a trailing wind.

 

[Texasmark]

Re: Optimax 115 / 135 fuel consumption

Well pilgrims, I know for a fact that the old cross flow inductions ran at least 2x to those numbers. Back when 35 hp was as big as it got, you could waste 2 ea 6 gallons of fuel on a Sunday afternoon without running very much.

On my '89 115 hp Direct Charged Merc, (like loopers but slightly different) I could run on a 10 gallon tank all day Sunday and have fuel left to fish the rest of the week. My current '02 90 hp looped Merc, carbureted, runs about 3 gallons of fuel for an outing and I primarily go out just to run it as fast as it will go......might wet a hook now and then.

Mark

 

[andy6374]

Re: Optimax 115 / 135 fuel consumption

Sometimes the Carb'd engine can even edge out DFI's at WOT fuel economy.

It's in the midrange and idle where DFI's really earn their salt.

 

[Silvertip]

Re: Optimax 115 / 135 fuel consumption

Come on folks -- let's have some real numbers here. Fill your tank. Run wide open for even 1/2 hour. Refill and post your fuel consumption (x2). Mark -- you are not really providing any numbers. 10 gallon tank all day is not a good measure. Is that at wide open throttle all day? As for the 90 Hp Merc, 3 gallons per outing is also a meaningless number. At wide open throttle I can guarantee it will flow a minimum of 8 GPH as my 75 HP flows 7.5 g/hr. All of this is a moot point if your boats are made of balsa wood. d

 

[imported_stinger]

Re: Optimax 115 / 135 fuel consumption

Thanks to all, I believed that the oil comsumption should have been 1%, from my experience it is about 2%!!! It was a surprise for me
On my previous Suzuki 60 HP carbs was about 1% on a 15" boat
Please note that I have an inflatable boat 20" and I drive usually from 4000 to 5000 rpm from 20 to 26 knots

 

[Texasmark]

Re: Optimax 115 / 135 fuel consumption

Silver sir I know that. Had I known I was going to be yakin on this board today I would have paid more attention. Probably the biggest variable is just how much of your engine's hp are you actually using the way you use it. I think that'is the real question. Even though you man be running your engine at WOT, how hard is it really working?

Diesel farm tractors are perfect example. I can take a given tractor and rake hay with it all day (very, very light load) and barely touch my fuel supply running at rated rpm's. However, I can take the same tractor, hook a plow to it (heavy load) and make a sizeable dent in the tank in half a day at the same rated rpm's.

Probably on the injected diesel engine when you set the throttle, you set an operating point on the injector pump related to engine rpm's. With no load, it takes little fuel from the injectors to get to this rpm. With a heavy load, the injectors have to put out more fuel to get there.....if you can get there at all.

On carbureted engines I guess it relates to intake manifold vacuum and the carb's venturi. Since vacuum is related to engine load, it would influence the amount of fuel sucked up for a given situation.

So, I guess if we really wanted to know the answer, we'd go to the Yammie tests you mentioned and conduct them while driving two different boats; one light fast one and one heavy one....same engine, propped properly of course to maintain the rated upper rpm limit. Course once you did that (tweaked the props), you should have balanced the loads on the engines so the consumption rates would probably be the same at WOT.

Course then the range will change, but as you said, probably not the gph so you get (one gets) the illusion that you are getting better fuel economy with the light boat which probably is what is affecting my judgement in what I said. Butttttt the engine vacuum wouldn't/shouldn't be the same, so the fuel consumption shouldn't be the same.

Course thinking about it some more, when I run a heavy boat, the throttle is usually firewalled while underway. When I run a light, fast boat, I usually have the throttle backed off to more of a cruise position.

So, yes, some numbers would help.....like you supplied. Grin

Mark