What Octane should you run?

[dantama]

A Denver news station did a story recently about stations that have water in their gas tanks from improper drainage around the underground tank lids.

I can't remember the figures, and couldn't find it in a search, but some stations had like 3 inches or more of water on top of the gasoline inside the tanks.

If you are at your favorite station after a rainstorm, when things are dry, but puddles are still around, you might want to look and see if water puddles around the metal lids going to the tanks.

Originally Posted by Dan Lund

...some stations had like 3 inches or more of water on top of the gasoline inside the tanks...

I wonder who reported that? Gasoline floats on water you know.

[blowndodge]

I was wondering the same thing. That's why when the station gets a new load of fuel you should wait for awhile because the water and sediment on the bottom gets stirred up.

[radco]

100 mile so far on 89 Oct. on my 04 1500 FI.. and I still have PLENTY of GAS and the TANK has alot as well. ::) Rich

I've always ran premium (91) Yesterday I decided to try mid-grade (88) just for fun. Bike ran flawlessly; never pinged even when I rolled on in 5th at 55mph. Next time I fill up I'll try 85

While cleaning the bike, I had the seats off, and for the first time actually read the smog information sticker under the seat. It says the bike was certified with 95 octane ROM (Research Octane Method) which isn't the same as the MOM (Motor Octane Method.) These are also known as RON and MON respectively. 95 octane ROM is aparently "regular" gasoline in Europe.

Gas sold here is 91 octane, but that's the average of the numbers generated by the two methods. So how do these compare?

(From Wikipedia.org: "Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90."......Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.)

So *IF* the MON is 8 to 10 lower than the RON (let's say 8) then the average will be 4 points above the MON or 4 below the RON. That means that our "average" 91 octane will be the same as 95 ROM.

However, as posted at Wikipedia, octane number isn't truly the measure of octane, but just an equivalent measure of whatever's there: so everything has an "octane number" depending on how it burns in the test.

Ethanol has a very high octane number. It's RON is 129 (MON = 102 and average is 115.5) and this is one reason why we're seeing so much ethanol in the gasoline here. It raises octane.

But, as everyone who uses it has found, it clearly reduces performance--which stands to reason because the higher the octane numbers, the lower the potential to burn. If you want to raise the octane number you can just pee in the gas tank; but I don't have to tell you what that would do to performance. ;)

Anyhow, what we're buying as Premium, the Euros are buying as Regular. I don't wonder that they're paying more for gas if, in addition to all their taxes etc., they are actually buying better gas.

Also, I'm reading a lot on the web about how the octane listed on the pump is not the octane people are actually getting. Typically it seems a bit lower. Maybe part of this is because alcohol evaporates faster than gasoline, reducing the octane. Maybe people are just screwing up, and maybe we're being cheated as well.

Note that adding SeaFoam and similar products will increase the octane number.