87. Going to try 91 someday when the prices go down.
But i've also been known to use 2-stroke oil...

Quote from: Ed_in_AzStrictly Super from the big four. Chevron, Texaco, Shell, 76. I might waste a buck over the month not buying the cheap stuff.

Where do you think 'joes gas and go' gets his gas....he doesnt have his own oil fields...it all comes from the same place...gas is gas

I used to think that way too....  And experience proved it.  Until about 2-3 years ago.  Now when I fill up at "Bobs gas" I get pinging with my car and my GS runs like the choke is on.  I know there are only so many refineries (130 or so in the US) and gas SHOULD be gas but I DO see(hear) a difference when using the cheap stuff.

Now I DO agree that going for the higher octane IS a waste.  If you get no pinging at 87 then using that is best.  The higher octane is exclusively for higher compression engines.  The octane molecule actually DOESN'T burn as well as the smaller chained heptanes and such and it prevents pre-ignition during the higher compression.  Someone here has the formula for octane as his signature.  An 87 gas is 87% octane and 13% heptane (OK there are additives too so lets make it 12%).  The 92 octane is 92% octane and 8% heptane.

For some reason where I live 87 and 91 are usually priced the same, with 93 being .10 higher.  So generally I go with 91, but I have used 93 and 87 with no discernable difference in butt-dynometer, engine sounds, or mileage.

I have noticed that Ethanol blended gas does make a difference.  No, I'm not talking the 85% ethanol blends, I'm talking the 10% blends.  I do often think I can feel a drop in acceleration when using ethanol and I always get a 5%-10% drop in mpg when I fill up with an ethanol blend.  Seems I sputter to reserve at around 200-210 miles using regular gas, and around 180-190 when using 10% ethanol blends.

Quote from: joerockerAn 87 gas is 87% octane and 13% heptane (OK there are additives too so lets make it 12%).  The 92 octane is 92% octane and 8% heptane.

I knew that the higher the octane the more resistant a gas is to predetonation due to compression, so that's why high compression engines require high octane gas.  But I've always wondered what the numbers actually mean and have been to lazy to look it up.  Thanks for the info, but it brings up a question.  If the number corresponds to the percentage of octane in the gasoline, how does that work with racing gasoline that's labeled 103 octane?  Other additives that make it act like it's 103% octane?

Up until a couple of years ago we had a gas station in town that sold it, expensive as hell (like $3/gallon when regular gas was $.98/gallon), but I knew people that swore by it for their street rods.

Ok, I found a link talking about this....
http://www.scuderiaciriani.com/rx7/gas_faq.html

Octane isn't a percentage.  It's an arbitrary number.  There are three measurements of octane - the Research Octane Number and Motor Octane Number (RON and MON) are often used outside of the US, while the US uses Anti-Knock Index (AKI), which is the arithmatic mean of RON and MON.

Once again - octane measures resistance to detonation.  It does not measure energy, it does not measure speed of burn.  If your engine is not detonating, you will see no gains from higher octane.

Here's a good reference:
http://www.repairfaq.org/filipg/AUTO/F_Gasoline6.html

Well in reality it is a number that WOULD be a percentage IF gasoline was made with just heptane and octane.  BUT since gas in the real world is made of all kinds of stuff, it is the final result number of whatever the gas contains that behaves just like a mixture of pure heptane and octane.  Mix 87% octane with 12% heptane and you have 87 octane gas.  Mix 80% octane with 10% heptane and 10% all the other crap (oxygenators, alcohol, whatever) and you end up with a fuel that burns the same way 87% octane would.  Understand?  Since we're not in a chemical engineer forum I think it's accurate enough to say it's the percentage of octane.

This is a general motorcycle forum, how technical should we get in our descriptions?  When someone asks about riding, should we explain that in the subatomic world you're not actually riding anything.  That their motorcycle is actually more (much more, on the order of billions) empty space than solid.  That at the atomic level the neucleous is like the sun and the electrons are like the planets with a similar ratio of empty space between them.

I don't think people need to know "the whole story" in all its gory details to get an answer to their question.  Do they need to know WHY different compounds and ratios of materials in the tires effect their "grip"?  I think it's enought to say tire X is stickier than Y but doesn't last as long.

Am I being a duck?  I don't mean to...  

Just trying to explain "in simple terms" how gas and octane work and are measured.  Sure. it's just an arbetrary number.  But it represents a ratio of heptane to octane.  It's like horespower.  Is it the power of 1 horse?  No, all horses have different strengths.  BUT it IS a representation of the power of one horse.  It's something like 33,000 pounds one foot in one minute or moving 330 pounds 100 feet in one minute.

Regular, regular and regular.  Don't forget the Castrol GTX 10/40 and she will be very  happy.