Stndard or super fuel pros and cons

[GBC]

Can you get 91 octane fuel that is ethanol free? All the stuff in the city seems to have it. I have run 95 in boats for that reason alone for a long time.

[ericcs]

i use the yellow 91 shell bowser, no ethanol in that!

[TheRealPoMo]

I think it may have some ethanol in it. Up to 1% before they have to advise I have heard.


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[ericcs]

hmmm, i could be eating my words!

https://www.colesexpress.com.au/shel...-unleaded.aspx

[fishtragic]

I used 98 whenever possible and sometimes 95 if i had to in a hpdi and was still faultless when i sold it at 1400hrs, new 4stroke motor was recommended to use 91 by the manufacturers website and now im told by the dealer to use 95. Bottom line is the higher octane fuels are cleaner an more bang for buck in my limited knowledge of fuel science.

[billfisher]

The first reply was closest to the mark, ie low compression engines (ie outboards) will not perform better with high octane fuels. Though there is one proviso in that different chemical bonds have different energy content so it is possible if the fuel is a blend which has a higher energy content then your outboard will perform better. Maybe give premium a try and see if you notice a difference.

[TheRealAndy]

limited knowledge of fuel science.

At least that part is accurate.

[stevej]

higher octane ratings allow you to advance ignition more for more hp
in my classic car on 91 I can run 8 degrees of advance, I just replaced the engine with a new race spec engine and am now running 98 I can run 12-13 degrees of advance.

unless the outboard can detect fuel type and adjust ignition you are gaining nothing performance wise
you will gain more detergents which can be detrimental to 2 stroke oil in kart engines we had issues with full mineral oils breaking down at 18,000 rpm

some use ethanol to boost octane racing but with a decreased energy rating hence you burn more for the same distance, some use other volatiles which if left for a few weeks in a boat tanks thats vented to the atmosphere will just evaporate off and your back to 91 or worse

people can believe what they want but 91 with no ethanol would be what I would use for any outboard rated to run 91 as per the manual

[juggernaut]

Couple of interesting articles I came across on the topic

https://www.tradeboats.com.au/traile...till-aint-fuel

and updated

https://www.tradeboats.com.au/traile...utboard-motors

[up the creek]

maybe scottar has never had a problem as it works just fine in little engines, which brings me to my point, racing or drag cars use high octane fuel and guess what they rebuild them all the time not just from high speed and revs but the fuel burns hotter in high octane fuels , so you have to ask yourself, does most smaller outboards need high octane fuel??? i believe in my opinion 91 is just fine and safer for small engines..

Maybe I am just lucky but in 30 years of boating running all sorts of two stroke engines - premix, old school oil injection and for the last 5 years an E-Tec, I have never experienced any sort of fuel issue running standard grade fuels - even with periods of lay up of 6 months without running any sort of additive. I don't bother topping off tanks after a day out - I refuel the day I am going but sometimes that isn't a lot of fresh fuel going in and at times engines are run on year old fuel on the hose at home. I can see the possible benefits with modern 4 strokes with variable valve timing though.

[stevej]

race drag cars run hotter cause they run them lean and advance timing for max hp
well beyond what's normal in a road car, speed costs money and they are prepared to pay the expense to win

so they rebuild engines cause they want to to win not because of fuel

[Heliduck]

The Octane rating for fuel does not designate calorific value, it designates the resistance to detonation. The higher the octane rating the higher is the fuels resistance to detonation when vaporized, that's why it is used in high performance engines which have high compression ratios & advanced spark timing.
As previously mentioned, the manufacturer does a lot of research on suitable fuel types & they want to advertise their product as the best for fuel economy & emissions so I'd suggest their recommendation would give you the best results for an unmodified engine.

[up the creek]

spose 1 way of puttin it,,, u most dont need 98 for ur lawnmower and 91 fuel is still fuel it works.. all the clever marketing tells you to use 95 or 98 as it does this and that,, and yes it adds a little more power to high performance engines. so one way maybe of putting it is.... smaller outboards 30hp and under 91 will be, well sufficent. if you want more hp get a bigger engine 98 aint gonna make a 2-30hp a speed boat.. but i believe no matter what anyone says. a little engine running cool is vital and higher burning fuel can get ur motor hotter and they dont like that.. as scottar said hes always run 91 and no problems.. i dont think a few drops less fuel or 4% hp gain is worth heating little motors up...

[Jason Green]

Just my two cents worth the last few trips I have been running 91 instead of 95 or 98 and my Yamaha gauge is telling me my motor has gone from a average of 2.2 km to the litre to 2.4 at 4000 rpm so now I can go faster and still get my average consumption that I like to work a trip out on


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[up the creek]

no doubt you will save fuel on 98,, is it a bigger hp engine? ... i got a 12l tank on mine lol so in my case i might not save much..