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Old 02 October 2008, 19:46   #1
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Gasoline Octane & Performance

Have been reading several engine tech manuals in which it's specified that high octane unleaded gasolines performs and cleans the engine better as having better gas cleaners compared to lesser octane unleaded gasolines.

Ok for this point, was wondering if using unleaded premium 95 octane gasolines compared to same 90 octane would make a difference in speed/engine performance. Don't know if it's my idea but when using 95 octane compared to 90 feel the sib/engine performing much better, with instant punch on the throttle. What are your thoughts about this issue ?

We only have 90/95/97/98 unleaded pure gasolines, with no alcohol mix whatsoever.

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Old 02 October 2008, 20:48   #2
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Our minimum is 95 but there are different ways of measuring it. To think in WW2 Britain had 150 octane!!!

Most engines will only benefit if they are tuned for it. Altering timing and mixture etc. Some modern computer controlled engines haver a sensor which will allow you to take advantage of better fuel.

Having said that most engines will benefit a little in smoothness etc if your wallet will stand it.

Just remember that fresh low octane is better than stale high octane!!!
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Old 03 October 2008, 02:29   #3
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loco - I think you would need to try it to see in your engine, but I doubt it will make a huge difference. as cod says there are differences in how octane is measured in the US and Europe so be cautious when comparing people's claims.
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Old 03 October 2008, 04:10   #4
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I'm not really sure why its sold in the UK as I have never found any difference in any car engines i've tried with the higher octane stuff. I can imagine it giving a small 2 stroke a little edge though, .. maybe my strimmer is crying out for super unleaded and I've denied the little fella all these years
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Old 03 October 2008, 05:32   #5
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I notice the difference on the bikes between unleaded and super-but all 3 are carbed. Saying that, it makes as much difference if I stick a tablespoon of tcw3 in the tanks
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Old 03 October 2008, 07:06   #6
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Stock setup theirs zero benefit and pretty much all engines are sold to run on low octane fuel. Engines especially 2 stroke with high compression heads, big bore carbs or throttle bodies, ect.. than you would pretty much have no choice but to use higher octane fuel.

Just keep your set up properly tune all the time and you'll have no issues.

Been there done that.

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Old 03 October 2008, 12:14   #7
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loco - I think you would need to try it to see in your engine, but I doubt it will make a huge difference. as cod says there are differences in how octane is measured in the US and Europe so be cautious when comparing people's claims.
Pol, to compare will need to have 2 tanks available, one with 90, other with 95, get a gps and on very calm waters full throttle same given distances with both gasolines to compare: same or better performance. The 90-95 price difference is not a big pocket issue, the largest engine used is a 30 HP, can have a full day divertimento with just 3-95 gas/gal/oil for about $ 15.00. So will stick with 95 octane for the moment. Thanks for all inputs fellow boaters.

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Old 03 October 2008, 14:06   #8
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gasoline octane &performance

I read the same at begining of the summer and checked with my mariner dealer who advised there was no benefit in running the higher stuff, the most important thing was the oil!
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Old 03 October 2008, 14:50   #9
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I read the same at begining of the summer and checked with my mariner dealer who advised there was no benefit in running the higher stuff, the most important thing was the oil!
Maybe run the slight higher gasoline because of having better cleaning components as advertized by gasoline stations, but who really knows. Other issue, would both gasolines form the same amount of carbon builup inside engine ?
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Old 03 October 2008, 14:56   #10
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Maybe run the slight higher gasoline because of having better cleaning components as advertized by gasoline stations, but who really knows. Other issue, would both gasolines form the same amount of carbon builup inside engine ?
One of the things he did tell me to stay clear off was the supermarket fuel as it has to much sulphur in it and tends to go off quicker especially in deck tanks.
J
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Old 03 October 2008, 18:14   #11
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to compare will need to have 2 tanks available, one with 90, other with 95, get a gps and on very calm waters full throttle same given distances with both gasolines to compare: same or better performance.
yes but bear in mind the benefit might be fuel ecconomy, or acceleration which won't show up so clearly on the GPS
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Old 03 October 2008, 18:32   #12
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One of the things he did tell me to stay clear off was the supermarket fuel as it has to much sulphur in it and tends to go off quicker especially in deck tanks.
J
Id agree generally- but Tescos super unleaded is the 2nd best out there as far as tuning is concerned-the best is Shell's V Power. When ive been remapping ecu's on cars you can run a lot more ign advance with these fuels without any detonation occouring compared to any other "super" unleaded.
But as said before, you dont gain any performance on a std engine unless it has the ign timing altered and fuel leaned out to make use of the higher octain. Not all cars are mapped to run on low octain, I used to have a BMW M3 that stated in the manual that it should be filled with a minimum of 97 ron fuel(super unleaded).Jap import cars are also mapped for high octain.
As far as 2 stroke's are concerned(never tuned them for high output), im not sure whats best to do with the ignition as ive read in some cases its better to lower the advance(skimmed heads/high compression), and others to raise the advance.

Locozodiac-fill up with a tank of the good stuff and advance your ign a couple of degrees(easy to to on your Tohatsu's), lean the mixture out a bit(keep an eye on your plug colours) and you should get a crisper throttle response and gain a bit of power + gain a bit of fuel economy while you're at it!!
Just dont lean it out too far - again, keep checking the plug colours are OK.
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Old 04 October 2008, 08:53   #13
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One of the things he did tell me to stay clear off was the supermarket fuel as it has to much sulphur in it and tends to go off quicker especially in deck tanks.
J

Believe that and you will believe anything - there are only a small handfull of refineries in the UK and the fuel can come from any of them. There are strict EU rules on fuel and it is all the same stuff excluding certain "special brews"!!!
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Old 05 October 2008, 09:34   #14
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Locozodiac-fill up with a tank of the good stuff and advance your ign a couple of degrees(easy to to on your Tohatsu's), lean the mixture out a bit(keep an eye on your plug colours) and you should get a crisper throttle response and gain a bit of power + gain a bit of fuel economy while you're at it!!
Just dont lean it out too far - again, keep checking the plug colours are OK.
Thanks for the imput, but all my Tohatsu's are running great with 95 octane, nice starts, acceleration, etc, and still factory adjusted. One issue that don't get clear, personally don't like to play with engine settings if engines are working ok, if need to, with a vernier measure all distances, gaps, etc and take a close-up photo on area before re adjusting, so in case need to put back as was before will do so with no prob.

Was the air gas mixture screw supposed to be just for idle (ralenti) speed adjustment only, as having un adjustable fixed air/gas inside jets according to manuals. Or this mixture screw works also when at any speed different from idle ? Any ideas.

The issue of taking the plugs out to see a brown like color, must be done after a full wot for some time, that is stop engine/take plugs out to check ? What moment would be the correct procedure to check this out ?

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