Gas grades

[wacky941]

I don't mean to sound argumentative but this information goes against logic.

Higher octane gasoline actually tends to burns slower, thus it resists detonation better. It does not have more energy per unit volume.

Engine designers can take advantage of higher octane fuels ability to resist detonation by increasing the engines compression ratio, or advance the ignition, both of which will extract more power out of the fuel and increase mpg. Modern engines typically have detonation sensors (called knock sensors) and automatically adjust the ignition timing to take advantage of high octane fuel. Some car manufacturers list two hp ratings for their engines: normal rating using regular fuel, and a high performance rating when using premium.

So if we run premium fuel in our GS without advancing the ignition timing (or the compression ratio) it's not logically possible to get more mpg from our engines. It could be that the particular brand of premium fuel you are using is has less alcohol than in the regular fuel, in which case your story would make since since alcohol is known to reduce mpg. I don't know but the octane alone can not do what you say.

I agree with this.

I pretty much use nothing but regular unleaded, I have found that for some reason (I don't know why) that my vehicles get better gas mileage when I fill up with Shell gasoline as compared to Chevron and Texaco.
For example, my Nissan Titan truck using Chevron or Texaco I get consistently 11mpg normal city driving, but when I fill up with Shell my mileage is 15mpg and if I use Shell while on the highway I get 19-20mpg, not bad for a Titan. I tried it in my wifes Honda Civic with the same type results.

Just my .02 this is what I have found.

 

[tkent02]

A very poorly tuned engine could run less badly on premium, say if the timing was far too advanced, slowing down the burn with the higher octane could result in better mileage. Or if it was lean and pinging slightly all the time, premium would make it less of a problem. More likely it's the alcohol content, even a small change in content makes a HUGE difference in mileage.

 

[850 Combat]

I have been running premium in my GS1000G lately. I was a little afraid to, but it seems to be working fine.

It is left over from summer of 2006, I have been draining it from the tank of my old autocross car which I hope to have back on the road this week.

six year old premium rocks

 

[Steve]

]... six year old premium rocks

But FRESH regular will roll.

.

 

[Steve]

Engine designers can take advantage of higher octane fuels ability to resist detonation by increasing the engines compression ratio, or advance the ignition, both of which will extract more power out of the fuel and increase mpg. ...

Ed, you were so close on the rest of that, I had to clarify this part, too.

In reality, "premium" gas is a Band-Aid that allows the use of higher compression, which is what really makes the power. The added compression adds heat, which can ignite "regular" fuel before the spark lights it. "Premium" gas is harder to light, so it waits for the spark.

Because "premium" gas also burns slower, the ignition has to be advanced to light it sooner so it is completely done at the proper time. However, even when burned at the proper time, "premium" still contains fewer BTUs per gallon, so there is no more energy to be had by simply throwing some in the tank.

So, if you simply fill your tank with "premium", and your engine is working nearly perfect, you will see a small drop in power because the gas has less energy and it's not being burnt properly in the engine. Advancing the timing will at least get as much as you can out of it, but it's still less than "regular" gas.

If your engine seems to run better with "premium", it's possible that you have carbon deposits in the engine that are glowing a bit, lighting the "regular" gas, and the "premium" gas resisits that. Again, the "premium" gas is a Band-Aid to mask a problem that should really be fixed properly.

 

[radek22]

My '80 GS1100 gets more mileage and runs smoother on regular.

 

[1_v8_merc]

Just noticed guys....my 78 gs750 calls for at least 90 or 92 octane......

And the PO rebuilt the motor and re-grinded the cams for torque, and I don't know what else he did to the motor.

Should I keep running close to 90 octane?

I haven't had any pinging so far.

 

[Guest]

I run the lowest I can get away with without pinging, I ran 87 and detected a little pinging under a heavy load, so I went to 90 and that stopped.

 

[duaneage]

Running my bike in high temperatures last summer, and at high altitudes, I found 92 or 93 kept the pinging away. I also found a gas station that sold ethanol free gas in premium only.
I don't see a problem with spending 20 cents a gallon for 4 gallons of better fuel. An additional 80 cents isn't a lot of money. I wouldn't fill a 20 gallon car tank with it, especially since cars have computerized fuel injection that compensates for the fuel. Alas, we don't have that luxury. Gas today is watered down with ethanol, toulene, xylanol, and a host of other additives which do who knows what.

I'm not telling anyone what to buy, and I get razzed for "wasting" premium fuel on my bike but I really don't care what others think or do. If they want to buy my gas then they can pick the grade.

 

[7981GS]

Pick the one that doesn't hurt YOUR engine.

Daniel

 

[apopleptic]

My 1980 GS450 says to use 90+ octane. I usually get super (91 octane)
I know when I drive across the country in my car I buy whatever the cheapest grade is and I get quite a bit better mileage with 85 octane instead of 89+, but the regular they sell around here (PA) is 87 which seems to give me the worst mileage of all.

 

[koolaid_kid]

s

s

My GS always rattled (ping, pre-ignition) on 87. In any state I went, any brand, rattle. She never rattled on 92+. And the timing was not adjustable, so I was stuck. It really sucked when we pulled into some tiny town that only sold regular. I was stuck with the rattle.
After I installed the Dyna S, she seldom rattles on 87, so that is what she gets. Of course, I set the timing by hand, so I know it is close to perfect.
The GPz, well, is a bit different.
IMHO, every single engine is a bit different. Find the sweet spot for your particular engine by going down in grade until the bike rattles. If you don't get rattles on 87, use it. If you do, move up incrementally until it goes away.
This only applies to stock engines, of course. Modified and FI engines are a different story.

 

[bccap]

I was running 87 in mine until dechand43 posted this;

I have read quite a bit about "brown talcum powder type stuff" in carbs by people who think it's rust. It is NOT rust! I build bikes, and also work on boats, and this stuff showed up heavy in the fuel tank of one of the boats I worked on. Trouble was, the tanks were stainless steel, so this stuff could NOT be rust. I had to find out what it was and the results are in, after a LOT of research!
It seems that ethanol reacts to oxygen, and the resultant residue is the byproduct of the breakdown of the ethanol. It begins in around 90 days of sitting in the tank untreated. It sticks to the insides of the tank and then flakes off, in the consistency of talcum powder, and will go through regular fuel filters like they weren't there. To catch it requires a 10 micron or smaller filter. It loads up beneath the pilot jets and makes it nearly impossible to "dial in" the carbs to idle right. "Kreem" can help immediately to seal it off, but if ethanol fuel is left sitting in there untreated it will foul that too. It does come off the inside of the tank when the tank is "banged", much heavier, making people think it is surface rust knocked loose. Two solutions I have found;
Buy non-ehtanol fuel(fat chance here in the US, They actually want to pass laws to make the content 20% instead or the present 10-15%).
or;
TREAT the fuel with additives sold everywhere.
Otherwise you will just have to ride hard and a lot so the fuel never gets old! ;-} I know, a third, sorry but I just had to put that in since it is my personal solution.
I bought a PAIR of GS850G's for 460 bucks and found this stuff in them. The first one I got running (and put 8K miles on in the first 7 months I had them) had this stuff under the rubber plugs that the pilot jets live under in the CV32mm carbs, and it has been one hell of a "chase" getting it cleared out!
If you have to leave the bike sit for more than a very short time, treat that fuel. Carb cleaner does not clean this stuff up either! The prep chemicals used for preparing the inside of a tank for "Kreem" works though.
Just thought I would pass this along. Can't fight what you don't understand, right? :-}

I switched to premium and noticed the bike running smoother and quieter.

 

[Guest]

My '83 has a shaved head and five degrees advanced timing, and it still runs great on regular.

 

[Guest]

I do agree that the "corn gas" as i call it sux, i try to not use it if possible.

 

[Dakotakid]

(Rolling eyes)...I run nothing but 10% ethanol in my GPZ 750, GS 850, and both Yamaha 500's at 88 oct. They run GREAT and I have no ill effects...no tank rust....no deteriorating rubber in the carbs.....just good power. Only once, in 100 heat, at 5000 feet elevation, on a long up-hill did I get the GS to lightly ping.

I realize a lot of you guys idolize Dick Cheney...but, I don't and I run lots of ethanol. I actually run at least 50% booze in my fuel injected VW gas rigs and life is great! Been doing it for years. Be careful whose gas you whiff!!!!!!

 

[81GS750]

Regular unleaded in all my bikes except for the turbo Yamaha, it get premium.