For those that advocate using 87 octane in these bikes

[themess]

...

An additional advantage with stock machinery is the richer mixture resulting from the denser high octane fuel provides an additional method of cooling for our already hot engines....

Octane and density are not related. Nor are octane and mixture. Study up on this.

However, engines can be tuned to require higher octane fuels. Performance will not necessarily improve if this is done.

[bigskybldr]

The Suzuki manual for my bike says "Gasoline used should be graded 90 octane or higher in Research Method, preferably unleaded or low-lead."
I know gasoline isn't the same as it was back in 1977 so I've tried different brands and different octanes. I didn't notice any pinging or knocking, the plug readings looked the same on all the grades.
I now only run the 87, it less expensive and from what I could tell, my bike runs good on it.

[themess]

...I now only run the 87, it less expensive and from what I could tell, my bike runs good on it.

You have reached the same conclusion as almost all GSR members who run stock engines in good tune.

[850 Combat]

All of my 1000Gs can be made to ping on 87, even the one with the 1100G motor. They can easily be ridden to avoid that as well. These 2 valve bikes don't have quick burn cylinder heads, the amount of advance needed proves that.

My 850s never ping on 87.

[WilliamGLX81]

First post didn't go through, so I lost my quote... anyway
Air is ~78% nitrogen, so you're not really getting much advantage from 95%+ nitrogen gas.

Also, I've been told that higher octane burns hotter. Had a mechanic who killed a VW bug engine with heat in mexico because they only had 110 octane. I don't know how scientific it was, but still.

And the price difference has dropped %-wise for years. It's like 25% the cost difference it used to be when it was $1 a gallon. I have to run premium in my 90 turbo volvo (which only has 8.7:1 compression when the turbo is not spinning). As far as I know, the only reason for the price difference is to discourage people from unnecessarily running fuel that requires more refinement than they need. That and I'm sure that 10 cents a gallon has some impact on profits, but it's hard to believe it's much when gas is $4+ per gallon.

Yes, it sucks that alcohol raises the Octane number because it's not actually octane.

[themess]

...Also, I've been told that higher octane burns hotter. Had a mechanic who killed a VW bug engine with heat in mexico because they only had 110 octane. I don't know how scientific it was, but still.

And the price difference has dropped %-wise for years. ....

Sorry, but you've been told wrong. The combustion temperature of higher octane gas would be, if anything, slightly lower than the octane of regular gas. However engines designed to require higher octane gas probably have higher combustion temperatures.

Octane rating is a measurement of resistance to precombustion or detonation. Diesel engines work without spark plugs. As the piston compresses the fuel-air mixture, the mixture increases in temperature. The "ideal gas law" describes the relationship:

PV = nRT

P is pressure
V is volume,
n is the amount of gas
R is a proportionality constant
T is temperature.

When the volume going into a cylinder is the same each time, the equation boils down to pressure x volume = temperature. As the piston compresses the mixture, pressure and temperature rise. When the mixture is compressed enough, the temperature rises to the autoignition temperature, where burning starts spontaneously.

The higher the compression ratio, the higher the temperature of the fuel-air mixture.

If the compression ratio is high enough, gasoline can also start to burn prematurely, or away from the flame front that is supposed to emanate outwards from the spark plug. That is called "knocking." To prevent this early combustion, chemicals are added to the gasoline. Slower burning gasoline has higher octane numbers.

Higher compression engines put out more power than equivalent, lower compression engines. The gas-air mixture gets hotter before the spark, which increases the chance of knocking.

Price differences between different grades are now larger than they used to be, but are a smaller percentage of the total price.

[razor02097]

There was a comment already about the first gallon pumped is whatever octane the previous guy pumped. That is 100% true. I don't see the point of putting in higher octane fuel than the factory recommends.

I've heard a lot of BS over the years. Higher octane doesn't mean the fuel burns hotter or better. Same for racing fuel. I've seen at least 2 cases someone ruining their O2 sensors or catalytic converters because they put freaking leaded race fuel in their late model cars. Hotter spark plugs aren't for extra horsepower they are to help reduce the chances of fouling and running heavier weight motor oil does not make the engine last longer, it makes the oil pump work harder.

The best advice I have ever been given was when I was told to plant my nose in the owners manual. The manufacturer built the darn thing I think they know best. Unless you modify your engine to increase compression over factory specs, buying fuel with an octane rating more than what the manufacturer recommends is a waste of money period.

[Douglas]

I've been using Shell 91 because in Canada it doesn't contain ethanol

[850 Combat]

There was a comment already about the first gallon pumped is whatever octane the previous guy pumped. That is 100% true. I don't see the point of putting in higher octane fuel than the factory recommends.

I've heard a lot of BS over the years. Higher octane doesn't mean the fuel burns hotter or better. Same for racing fuel. I've seen at least 2 cases someone ruining their O2 sensors or catalytic converters because they put freaking leaded race fuel in their late model cars. Hotter spark plugs aren't for extra horsepower they are to help reduce the chances of fouling and running heavier weight motor oil does not make the engine last longer, it makes the oil pump work harder.

The best advice I have ever been given was when I was told to plant my nose in the owners manual. The manufacturer built the darn thing I think they know best. Unless you modify your engine to increase compression over factory specs, buying fuel with an octane rating more than what the manufacturer recommends is a waste of money period.

Not 100% true

Not every station has multi grade pumps. The closest non ethanol station to my house in Tillamook OR has a separate pump for the non ethanol BP premium I like to leave in my vehicles when they are parked.

Non Ethanol seems to have a better shelf life in the tank.

[Dj66]

High octane

Higher octane fuel burns a little slower which is good for long stroke engines with poorly designed cylinder heads(Harley Davidson). These bikes should not need it in stock form.

[earlfor]

You stirred the pot, so don't cry when ums gets spattered... I still think it's an interesting question, how does fuel grade and/or octane rating (I didn't mention octane either, just asked a question) compare from two stroke to four stroke engines? Impossible to tell from original fuel specs, but I bet a lot of folks that have both bikes and run on modern fuels have insight.

Two strokes usually had low compression ratios around 7 to 1, so high octane fuel was not needed.

[razor02097]

2 strokes can suffer from detonation but that is typically due to lean air/fuel ratios and not so much with octane.

I have heard that you should use synthetic 2 stroke oil with pump gas containing ethanol because the oil doesn't mix well with the ethanol and the ethanol can potentially separate causing oil starvation... I don't know if it is true or not but since synthetic is a buck or two more per quart I don't chance it.

[themess]

I've been using gasohol in my two-stroke lawnmower and string trimmer for many years. I've never seen any sign of separation or of cruddy fuel.

[JayWB]

PV = nRT

P is pressure
V is volume,
n is the amount of gas
R is a proportionality constant
T is temperature.

When the volume going into a cylinder is the same each time, the equation boils down to pressure x volume = temperature. As the piston compresses the mixture, pressure and temperature rise. When the mixture is compressed enough, the temperature rises to the autoignition temperature, where burning starts spontaneously.

The higher the compression ratio, the higher the temperature of the fuel-air mixture.

If the compression ratio is high enough, gasoline can also start to burn prematurely, or away from the flame front that is supposed to emanate outwards from the spark plug. That is called "knocking." To prevent this early combustion, chemicals are added to the gasoline. Slower burning gasoline has higher octane numbers.

To this I'll add that the actual knock is caused by the extremely violent collision of the multiple flame fronts. An inspection of an engine that has suffered a lot of pre-ignition pinging or knocking reveals that the pistons have lots of little dents on them, looking like someone has been hitting them with a ball peen hammer.

[limeex2]

The worst culprit is ethanol. It replaces fuel. to get the proper a/f ratios much more is needed with alcohol. Unless it was jetted and/or designed to run these fuels, it is running lean. it has a very poor shelf life and because it has sugars in it can lead to more rapid carbon build up.