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Discussion Starter · #1 ·
Just for the heck of it I am testing out 89 octane gas in the bike. I am now on the 5th tank of 89 octane gas and so far so good.
The bike is a 103 with flat top pistons & stock heads with a cam, intake and exhaust upgrade.
I always used premium fuel 91 to 93 octane fuel and only used lower octane gas once in a emergency situation but I decided to see how the bike runs on lower octane fuel.
So far the mpg is the same with the 89 octane as it is with the 91 octane, I haven't had any power loss or pinging. I only ran the bike with the 89 octane in temps ranging from 65 to 92 degrees, I am not sure if the bike would ping with temp higher then that.
 

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I tried running lower octane back a few years ago when gas was right at $5 per gallon, my mileage only went down about 2mpg, but the performance wasn't the same. The bike didn't accelerate as well, especially when it was hot, I haven't tried it again since, and don't plan to.
 

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I used it on trips out west when high octane was not available. I couldn't tell any difference. I was not testing it either by red lining the engine and such either. :)
 

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I have been running 89 in my 2015RGS because I believe that is what the manual recommended.
 

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My 2011 RGU has a recommended octane requirement of 91, as listed in the owners manual.
I use 93, or any premium since most dispensers have the single hose system and may contain a 1/2 gallon or more of the the previously dispensed fuel, usually that is regular, 87 octane.
 

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Ya forgetting the other 10%, like a free gallon of Ethanol with every 9 gallon of BETX constituents of gasoline. Or the transfer filling subs lines of the tanker trucks from the previous fill, or even the spill bucket maintenance of the gas station. My bikes will run on 87 but I like to huff the 92 more better
 

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Pro stage 4 kit at low altitude with no dyno tune yet, gotta run 93 + booster till I can get to a dyno. Yall enjoy that cheap gas! I learned my lesson with this one. Never raise compression again!
 

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Since 91 octane is the highest we typically have here, and sometime not even that, I use my Power Vision tuner to do tunes for 87 and 89 octane. usually all it takes is to pull a couple degrees of timing and maybe richen the mixture a bit to keep the pinging away.
The Power Vision will show you how much timing the ECM is pulling to keep the detonation under control, and if you take note of the rpm and map readings when it's doing it you can go in and manually pull the timing out of the tune.
 

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I only run 89 or lower if 91 or higher is not available.
 

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Discussion Starter · #15 ·
The compression on my bike is around 10:1 so the bikes compression is above stock and I didn't need to adjust any timing to use 89 octane fuel. I haven't had any pinging yet and the bike performs just as well as it does on the 91 octane fuel (93 octane is not available out west).
 

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The compression on my bike is around 10:1 so the bikes compression is above stock and I didn't need to adjust any timing to use 89 octane fuel. I haven't had any pinging yet and the bike performs just as well as it does on the 91 octane fuel (93 octane is not available out west).
You going to keep using the 89 ? I been thinking about switching myself. I read an article that said , all octane was for is to stop knock, so if your not getting knock, your good. It went on to say the lower octane had a higher explosive rate , from what I understand, in return should produce more power, ounce for ounce.
 

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You going to keep using the 89 ? I been thinking about switching myself. I read an article that said , all octane was for is to stop knock, so if your not getting knock, your good. It went on to say the lower octane had a higher explosive rate , from what I understand, in return should produce more power, ounce for ounce.
What you say is correct.

There is SO much misunderstanding and misinformation out there about octane ratings, what they do, how much power they make, how they run etc.

Some very basic discussion may clear some of it up, at least for this audience........


Here is just one definition of "Octane":

What are octane ratings?

Octane rating is a measure of a fuel's ability to resist ‘knock’. The octane requirement of an engine varies with compression ratio, geometrical and mechanical considerations and operating conditions. The higher the octane number the greater the fuel’s resistance to knocking or pinging during combustion.



OK, but what exactly is knocking, pinging, and detonation??

Essentially they are all the same thing, with only slight differences. What it comes down to is knocking, pinging and detonation are all uncontrolled ignition of the air fuel mixture. Uncontrolled, as in happens before you wanted it to, which is supposed to be when the spark plug lights the mixture.
Detonation, pinging, knock is ignition of the air fuel mixture by heat and pressure in the combustion chamber, much like how a diesel engine works, only with gasoline. When it happens in severe cases your gas engine will indeed sound like a diesel. However it can often be a silent killer that you won't even know is happening, especially on a motorcycle with loud exhaust, until the damage is done.

So, then what's the difference between the numbers, 87, 89, 91, 93 etc?? What do the numbers mean?? What is the measurement??

Octane rating is tested by running various fuels in a variable compression engine that measures the point where fuel will ignite by pressure rather than a spark. 87 octane ignites at pressure "A", 89 octane ignites at a higher pressure "B", 91 octane at the next level, etc.
There are several standards in the ratings, 87 octane in the USA is not the same as in the UK, automotive fuel is not measured same as aircraft etc, but they all mean basically the same thing. The higher the rating, the more resistant the fuel is to heat-induced or uncontrolled ignition.

Also, as you may have guessed, and this is important. If a fuel at a certain level is harder to ignite uncontrollably, it's also harder to make it ignite in a controlled manner with a spark. It's just harder to get lit. The difference is often slight, slight enough that most might not even notice it, but under controlled conditions there is a difference and it is noticeable.

Being that 87 octane is easier to light than 91 octane, it will in many cases, start easier, idle better, be less prone to missing and stumbling, and will indeed make more power, AS LONG AS THE TUNING IS CORRECT, AND DETONATION IS KEPT UNDER CONTROL.

Making gasoline burn in a controlled manner and making the most power is a balancing act, but one thing has been proven over and over. All else being equal, if can run lower octane, and keep the pre-ignition/knocking/detonation/pinging under control, you will make more power. Conversely, if you run more octane then you need, you will make less power.

What it comes down to is that just throwing more octane at an engine when it really doesn't need or can't use it will most often hurt more than helps, as will taking octane away from an engine that needs it.
Higher octane is very often used as a crutch to cover poor tuning or other issues.


When I was deeply involved in building competition 2-cycle go-kart engines under very tight rule structures we had to get every tiny advantage we could. Fuel was only one part of the combination that I had to learn how to manipulate and deal with. A lot could be gained, even while staying inside the rules.
Let me tell you, convincing the next Jeff Gordon's father that his kid's "race" engine would be faster without "race" fuel isn't easy, but when it works it's a good thing.
 

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Good explanation, and I know that I've seen it somewhere before. I guess one of the reasons my bike runs better on higher octane is because the compression is higher than stock. I guess I could play with the MAP and tuning, but I'm one of those who believe "if it ain't broke, don't fix it".
 

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Discussion Starter · #19 ·
You going to keep using the 89 ? I been thinking about switching myself. I read an article that said , all octane was for is to stop knock, so if your not getting knock, your good. It went on to say the lower octane had a higher explosive rate , from what I understand, in return should produce more power, ounce for ounce.
I can't see any reason not to keep using 89 octane if the bike run good on it. I haven't tried 87 octane but I might do that sometime in the future.
Why not save a buck or two if you can which can add up to a big savings over time.
 

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I can't see any reason not to keep using 89 octane if the bike run good on it. I haven't tried 87 octane but I might do that sometime in the future.
Why not save a buck or two if you can which can add up to a big savings over time.
I agree totally, not being cheap, just frugal. :)
 
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