What Octane

[Mashby]

Hi All
Whats the prefered Octane of the XZ550
Cheers

[gbranche]

The proper answer is "the lowest octane that the engine will run on without pre-ignition/detonation (aka "knocking")".

Of course, that's probably not the answer you were looking for.

The way I understand it, octane rating is effectively a measure of how volatile the fuel is, with lower numbers meaning that the fuel is more volatile (i.e. it will vaporize more quickly). So, a lower octane fuel will actually burn more quickly/completely (due to it's higher volatility), but may actually vaporize too quickly, and will catch fire inside the cylinder before the spark plug has ignited it, which means that it actually explodes within the cylinder, rather than having a smooth burn. Those explosions are what the operator hears as "knocking".

In the summer, when it's warmer, and therefore when the fuel vaporizes more quickly, you may need to move to a higher octane fuel. During the winter, you can go back to a lower octane fuel. (Er, I guess I should qualify that for those who don't have the opportunity to ride all year, like those of us on the left coast do.)

As far as personal experience goes, I find that 87 octane petrol works just fine for me. I actually fill up with the cheapest gas I can find (I can see Lucky wincing now :o ). But, your experience may differ. There are just too many variables involved to state as a certainty which octane is best for your conditions/environment. The best thing to do is experiment.

Greg

[Lucky]

Actually I use the cheapest gas I can find too, as long as the fuel filter is good, no problem.

I use fuel de-waterer twice a season, Berrymans fuel injector cleaner once a year (full can in a full tank) and if I ever see the fuel truck at the gas station I go elsewhere.

as far as octain goes, the bike runs great on regular gas, probably would run better on a higher octain, but it'd be hard to increase the size of the grin on my face in the twisties anyway...

-Lucky

[QBS]

Luckey said it all.  Don't blow off his comment about the gas truck.  Been there.  Done that with a car.  Bought 14 gallons of 87 octane water.  Didn't hardly get out of the gas station.  It wasn't a positive experiance.  Cheers.

[silicon_toad2000]

well that opens my eyes a bit.
my first tank was 98 octane which is our premium, then i ran 94 which is our cheapie stuff. I dont think ive ever seen petrol here less than 90 octane. I'll have to start paying more attention.

[Lucky]

well your certainly paying more money, that's for sure...   :(

[glennw]

98 octane.. were you buying gas at the Airport ???

[gbranche]

S/T may be referring to a different octane measurement. Here in the US, our reported octane is actually the average/median of "research" octane and "motor" octane. The formula is "(research + motor)/2". The octane number reported in his location may just be the research octane number.

Greg

[glennw]

Greg...OK, Thanks, that makes it completely clear!  :-/

[gbranche]

Well, maybe these will help:

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

http://www.handymanusa.com/articles/octane.html

http://chemistry.about.com/cs/howthingswork/a/aa070401a.htm

This last one contains this paragraph:

Gasoline pumps typically post octane numbers as an average of two different values. Often you may see the octane rating quoted as (R+M)/2. One value is the research octane number (RON), which is determined with a test engine running at a low speed of 600 rpm. The other value is the motor octane number (MON), which is determined with a test engine running at a higher speed of 900 rpm. If, for example, a gasoline has an RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or 94.

For even more references, do a Google search.

HTH,
Greg

[silicon_toad2000]

well there it is, I have only ever seen RON mentioned, I haven't seen MON before except on my calender.

way too true about the price lucky, we're paying AU$1 per litre and i think there is about 4.5 litres in a gallon so about US$3-US$4 per gallon

I'll be asking about this MON thingy, give me a better idea about how our fuel here stacks up. The general consensus is that its S**T compared to what it used to be.

[Walt_M.]

Here is something to further complicate the measuring process, I have in front of me a 1 US gallon container that says 3.87L. As for what octane to run, whatever you want as long as it does not detonate. Just be sure to be a little cautious after a fillup. I have gotten the occasional bad tank of gas, even with no tanker truck in sight.