Octane rating - which fuel for bikes?

[ZooTech]

you do get better mileage with the higher Octane

Only if your fuel management system is capable of taking advantage of the higher octane content and derive more power from it. With more power from the same amount of fuel, you will yield higher mileage. Bikes generally are not equipped with the technology necessary to do this, however, so don't bother pumping premium if your bike calls for 87. At most you should step up to 89 during hot summer months, especially if your bike is strictly air-cooled, just to ward off detonation.

[oldnslo]

Fuggeddaboutit, Zoo. Opinion will prevail over science, every time.

[ZooTech]

Fuggeddaboutit, Zoo. Opinion will prevail over science, every time.

I imagine you're right!

I can't believe how much misinformation is flying around about such a simple topic. There are a million websites you can visit to get the low-down on octane ratings and what it all means, so there's really no reason to tell tales out of school or speculate on the subject.

[oldnslo]

The octane thing has been with us in one form or another since I started driving back in the '50's. I remember stories of more efficient combustion and cooler combustion, in addition to the gas mileage thing, all just stories. If a vehicle set up for 87 gets better mileage or runs better on 92, it needs a tuneup. If 92 was the real deal, every auto manufacturer would specify it for ALL their vehicles, making it easier to meet government mileage mandates.
I haven't even checked the internet, but I think just about any and all information on any subject can be found there. Except maybe gallbladder surgery at home using kitchen utensils.

[ZooTech]

The octane thing has been with us in one form or another since I started driving back in the '50's. I remember stories of more efficient combustion and cooler combustion, in addition to the gas mileage thing, all just stories. If a vehicle set up for 87 gets better mileage or runs better on 92, it needs a tuneup. If 92 was the real deal, every auto manufacturer would specify it for ALL their vehicles, making it easier to meet government mileage mandates.
I haven't even checked the internet, but I think just about any and all information on any subject can be found there. Except maybe gallbladder surgery at home using kitchen utensils.

Sorry, I came up short on the home gall bladder surgery...but I did find a fine example of the octane debate:

CHeck out this link for the Nissan Maxima. Notice how the engine specifications has a "1" next to it. Scroll down to read the fine print and you'll see the power output rating was based on premium fuel. Obviously most cars on the market today can advance engine timing enough to generate more power with premium gasoline, yet can still run on 87 with help from timing mentally challenged and knock sensors. Unfortunately, as you know (this is for the sake of everyone else because I know you get this already), motorcycle engine settings are more or less static and cannot make appropriate changes on the fly to either cope with less octane or benefit from more of it, whichever the case may be. Throwing in higher octane than necessary will do no harm, but may actually yield less power. Throwing in lower octane than specified can and will do serious engine damage. You need to run the minimum octane stated in the manual and take a pro-active approach in summer months and/or hot climates and step up a grade or two in order to cope with the added heat, which is a contributor to predetonation.

[High_Side]

you do get better mileage with the higher Octane

Only if your fuel management system is capable of taking advantage of the higher octane content and derive more power from it. With more power from the same amount of fuel, you will yield higher mileage. Bikes generally are not equipped with the technology necessary to do this, however, so don't bother pumping premium if your bike calls for 87.

My fuel management system consists of a couple of 48mm carbs yet it makes a difference. The manual says anything over 86 or higher will do, yet I consistently get better mileage with 91. (I've stated earlier that I've ran the cheap stuff in the bike with no ill effects). While some of us like to quote the hard data and essays written in motorcycle magazines, I prefer to establish a base knowledge and experiment to make my own conclusions. Science is great, but without real world experimentation it means nothing.

Fuggeddaboutit, Zoo. Opinion will prevail over science, every time.

John, if anyone elses opinon differs from your own they have to be wrong. Maybe if you belittle them they will come around, no?

[ZooTech]

My fuel management system consists of a couple of 48mm carbs yet it makes a difference. The manual says anything over 86 or higher will do, yet I consistently get better mileage with 91.

I don't doubt it. But it's more than likely due to your timing being advanced. A carbureted motorcycle has a fixed range of spark advance to work with...and if that range is biased with more advance from the get-go the engine may very well benefit from the higher octane fuel by igniting it earlier in the compression stroke and yielding more power. With more power output from the same volume of gasoline, you'll use less of it to achieve the same results, thus the increase in mileage.

[oldnslo]

It isn't my opinion, Bruce, but that's OK. Have it your way, Burger King.

[Gummiente]

the engine may very well benefit from the higher octane fuel by igniting it earlier in the compression stroke

But isn't that what causes detonation?

[ZooTech]

the engine may very well benefit from the higher octane fuel by igniting it earlier in the compression stroke

But isn't that what causes detonation?

No, pre-ignition happens when the air/fuel mixture ignites in the absence of a spark, either via excessive combustion chamber heat or more compression than the fuel is rated to tolerate, or a combination of both. All engines (that I know of, I cannot account for extreme odd-balls) ignite their air/fuel before the piston reaches TDC (Top Dead Center) on the compression stroke. How much before is the question. A car's more sophisticated EMS can sense a number of operating parameters and determine the optimum time for spark. Bikes, on the other hand, have fixed timing (there is some advance, but it too operates in a fixed manner) so you have to throw in the correct fuel for all the operating parameters involved and account for worst case scenario.