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Fuel Grade for EFI?
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Author:  schoolsOut [ Sun Sep 08, 2013 9:19 am ]
Post subject:  Fuel Grade for EFI?
A quick search found an older, short, thread regarding fuel grades, but I would like to get a current perspective. I generally run 89 octane in my 5.0 GXi. I don't have a problem dropping a couple of extra bucks into the tank with 91+ octane, but I was not sure if I should. What do you guys use? Boat seems to run great on 89 (marine stabil always added). Should I start using premium grade fuel? Will I see a performance difference or is it just easier on injectors and fuel system?
Author:  ric [ Sun Sep 08, 2013 9:38 am ]
Post subject:  Re: Fuel Grade for EFI?
Higher octane fuel just means it has a higher tolerance to compression before it self ignites from the heat.

It does not make an engine produce any more power than any other octane fuel. It has no effect on the fuel system than any other octane fuel. It does not clean anything out. It does not store better. It doesn't give you better fuel consumption.

Higher octane fuel just means it has more octane for high compression or forced induction engines that run extreme cylinder pressures so it does not pre-ignite on it's own causing detonation and breaking the engine. All marine engines are around 9.5:1 compression ratio. 87 octane is all they require.
Author:  298VISTA2000 [ Sun Sep 08, 2013 12:42 pm ]
Post subject:  Re: Fuel Grade for EFI?
Don't mess with something that is working for you but are you using ethanol or real gas?
Author:  230 Mike [ Sun Sep 08, 2013 12:49 pm ]
Post subject:  Re: Fuel Grade for EFI?
Your FW manual should say all you need is 87. By '05 that had pretty much become the spec. Many boats still run 89 only because 1) they fill up on the water and there are lots of marinas that only have 89 still, from the days when that was the spec for nearly all boats, or 2) the shade tree gear heads who think a higher octane must be better because its a bigger number and costs more.

Some boats, especially older ones, will do better on 89. All you need is 87. I've never heard of a stock boat that needed 91.

Also, from a chemistry standpoint the higher the octane the faster it loses its potential energy; not a good thing when off-season storage is involved.
Author:  schoolsOut [ Sun Sep 08, 2013 7:51 pm ]
Post subject:  Re: Fuel Grade for EFI?
298VISTA2000 wrote:
Don't mess with something that is working for you but are you using ethanol or real gas?

Pretty much everything around me is 10% ethanol, so that's what I use. I add an ounce of stabil for each 10 gallons because of that.

230 Mike wrote:
Your FW manual should say all you need is 87.

From the manual, "If fuels with 89 AKI pump posted (93 RON) octane number or higher are used an increase in power can be expected with EFI models."

Also, "CAUTION! Engine damage resulting from the use of a lower octane gasoline than 87 AKI (90 RON) is considered misuse of the engine. Any resulting engine damage will not be cov- ered by the warranty."

Because of this, I always use 89. Although it says that I can use 87, it also implies that 87 is the "minimum". Putting the "minimum" acceptable grade seemed questionable to me, but maybe that's what I should be doing. Based on the manual. I always considered giving 91 a try to see what that "increase in power" is all about.

Thanks for all of the responses. You guys are always a great help.
Author:  deafwish [ Mon Sep 09, 2013 12:12 am ]
Post subject:  Re: Fuel Grade for EFI?
A higher octane will reduce the risk of heat-soak induced detonation, common when pulling skiers or getting on plane.
If you use higher octane fuel, you can also dial in more timing.
Author:  230 Mike [ Mon Sep 09, 2013 4:06 pm ]
Post subject:  Re: Fuel Grade for EFI?
There's certainly nothing wrong with running 89. I fill up about 80% of the time off the water and only use 87 in those cases. 8 years so far and I'm happy with it. When I do fill up on the water, 89 is usually all that's available, so I use it and only wish I didn't have to pay for it.
Author:  Technologic80 [ Mon Sep 09, 2013 4:19 pm ]
Post subject:  Re: Fuel Grade for EFI?
When I used to be at a marina, I used e-10 free 90 octane because that's all they sold. Well, correction: They did sell a higher octane but the price per gallon was insane. 90 octane was expensive enough! :shock:

Since I moved to a house on the water in 2009 and keep the boat at my seawall in my backyard, I've used 87 octane E-10 and never had a problem. Marinas in my area are all making the change to E-10 too.

I dont get detonation, knocking, or poor performance with any fuel so far and when away from home port on our excursions, I have to gas up at various marinas.
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