dcc46 said:
Locally I can get 92 octane with 10% ethanol or 90 octane with no ethanol. Which is better for the bike and why?
I don't particularly worry about ethanol, because frankly the problems have been overblown. Every problem that anyone gets is now blamed on ethanol regardless of the cause. Some problems, especially in older vehicles may be related. If a manufacturer uses ethanol unsafe products in the fuel system these days they should be "sacked".
There are two things to worry about RON/AKI and detergent combustion enhancers. It is quite conceivable that you can have a low "octane" fuel that has good detergent cleaning properties but usually the low octane fuel is usually marketed as cheap fuel which means it also misses out on the extra good stuff because it is generally the price leader.
Ethanol on its own has a RON figure about 105, so is often used to boost octane ratings. You may find that what you get above is the same fuel, except the E10 blend is using the E as an octane booster. Ethanol also has some cleaning properties AND will absorb some moisture from fuel.
So there are two things going on here. The higher octane fuels will reduce knocking (short term damage) and the detergents and anti gumming agents reduce long term "cholesterol build up" in the fuel system. So using a higher detergent fuel with a high enough octane rating for your engine will be best long term.
It is very safe to use 98RON with no ethanol. The engine will stay clean and will probably never suffer pre-ignition even if the fuel has been sitting for a long time and some volatiles have been "blown off".
However here are some general things about fuels..
A higher octane fuel has less energy per litre available GENERALLY than a low octane fuel. (Ethanol is a good example of this)
Ethanol will cool the intake charge to the engine more than most of the other compounds in fuel.
A high detergent low octane fuel is hard to find.
The compression ratio is an indicator of the compressed gas temperature at TDC. Higher comp engines make the fuel air charge hotter when compressed than lower comp engines so as the outside air temp increases the compressed charge also gets hotter so the hotter it is outside the more important the octane rating is to prevent this. When I say outside I mean outside the combustion chamber, which includes the cooling jacket etc.
Maximum chamber temperature is reached at WOT AND only certain RPM. Generally lower RPM.
Higher octane fuels resist detonation for higher temps.
Here is a very basic breakdown on what fuel might contain..
http://firstfuelbank.com/msds/Tesoro.pdf
Code:
Gasoline 8006-61-9 100 300 900 300
Contains or may contain:
Toluene (a,b,c,e,f,g) 108-88-3 0 - 35 200 50 Yes 1000
Xylene (mixed) (a,b,c) 1330-20-7 0 - 25 100 435 100 Yes 1000
Pentane 109-66-0 0 - 20 1000 2950 600
Trimethylbenzenes, mixed isomers (a) 25551-13-7 0 - 4 25 Yes
Benzene (a,b,c,d,e,f) 71-43-2 0 - 5 1 0.5 Yes 10
Butane 106-97-8 0 - 12 800 1900 800
Ethylbenzene (a,c) 100-41-4 0 - 5 100 435 125 545 Yes 1000
Heptane 142-82-5 0 - 2 500 2000 400
Cyclohexane (a,b,c) 110-82-7 0 - 5 300 1050 300 Yes 1000
n-Hexane 110-54-3 0 - 8 500 1800 50 176
n-Octane 111-65-9 0 - 1 500 2350 300 1400
Ethanol 64-17-5 0 - 20 1000 1900 1000
Naphthalene (a,b,c,g) 91-20-3 0 - 1.1 10 50 10 Yes 100
Trimethylbenzene 1,2,4 (a) 95-63-6 0 - 7 25 125 Yes
Isopentane 78-78-4 0 - 20 not established
Styrene (a,c,d,e,g) 100-42-5 0 - 4 100 20 Yes 1000
Methyl tert - butyl ether (a) 1634-04-4 0 - 18 40 144 Yes
Ethyl tert - butyl ether 637-92-3 0 - 21 not established
Tertiary - Amyl methyl ether 994-05-8 0 - 20 not established
Alkanes, Cycloalkanes, Alkenes, Aromatic hydrocarbons balance
(b) Indicates that the Resource Conservation and Recovery Act (RCRA) has determined the waste for this chemical is listed as hazardous and must be handled
There are about 500 compounds in fuel and all fuels vary. Fuel mixing is still one of the great arts.
So, armed with that info you decide. All I can say is that I run the bike on good fuel and when I can't get it I don't stress too much. I don't stress too much about ethanol except when I think the "gas" station has got a high chance of old fuel OR has been wet recently. In fact any fuel is in danger from water contamination in floods.
Many bikes these days used with good oils and serviced regularly will last 200,000 miles, especially these big low revving beasts. Will you be running this bike that long or will it be traded at 40,000 miles?
Very complicated, but YAMAHA recommend using premium because it is an easy and safe recommendation.
