Bonneville America Forums Forums Technical Forums General Tech Grade of gas ?

When I bought my bike I asked the dealer if I should use high test, he told me it would be awaste of $, that I should use mid grade. It seems to run good on it, but I was wondering what everyone else is running. I havent made any performance mods.

As with any machinery, read the owner's manual. If it does not specifically indicate running 93 octane or higher, then doing so would be a waste of $$$$$.

I use mid-grade myself. Don't recall exactly what the book says, but it did not say 93 octane.

Owners manual says 89 Octane.

The book lists a minimum octane level thats why I asked. My truck doesnt recomend hitest but I get 7 miles more per gallon.

I usually get premium. I do get better mileage when I do. However when I get regular, or mid-grade the bike runs well on those as well.

I noticed something the last time I went to Utah. The octane levels of regular, mid, and premium are lower there than here. In Utah regular is 85, mid is 87 and prem was 91. Here regular is 87, mid is 89 and prem is 93. So getting regular here is like mid-grade in Utah.

Soren

There's absolutley no point getting a higher grade of gas than recommended with a standard compression engine - anything more is a waste of money. Octane is just a rating of how well the fuel withstands compression before it auto-ignites (which is what "pinging" is), so having fuel that can withstand more compression than your engine can deliver is useless.

Fuel companies would have you believe that some of the additives in the "premium" fuel make it worthwhile because they "clean" your engine... however in an engine fitted with carburettors at best the additives do nothing, and at worst they clog up the jets.

Matt

I use 89 octane in both my cars as well as in my SM. No problems at all. I use 87 in my gas power tools.

The ONLY concern with octanes are pre-detonation and/or dieseling when you shut the engine off. If you are having that and everything else is in tune, then move up a grade. If not, then stay with what you are using.

what the s.h.i.t you have on petrol station ?

here you can buy 95 or 98 last year in germany I was surprised when I seen 91 benzin but they still have a lot of 2 stroke cars was thinkng that only in Russia you can buy less than 90 octan In poland i was filling 95 like here but had to fill 98 coz on 95 had no power to overtaking mayby that is a reason of all yours mods ->CRAP CHEAP FUEL

89 octane is all you need so mid grade will do just fine.

Grzegorz,
Maybe this explains the number differences between here and there...

"Gasoline pumps typically post octane numbers as an average of two different values. Often you may see the octane rating quoted as (R+M)/2. One value is the research octane number (RON), which is determined with a test engine running at a low speed of 600 rpm. The other value is the motor octane number (MON), which is determined with a test engine running at a higher speed of 900 rpm. If, for example, a gasoline has an RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or 94."

"High octane gasoline does not outperform regular octane gasoline in preventing engine deposits from forming, in removing them, or in cleaning the engine. Consumers should select the lowest octane grade at which the car's engine runs without knocking. Occasional light knocking or pinging won't harm the engine, and doesn't indicate a need for higher octane. On the other hand, a heavy or persistent knock may result in engine damage."

Same stuff, different rating system. A bit like degrees C vs degrees F.

When I checked, I found that for a 3% increase in price, for 93 octane, over 89 octane, my mpg increased 10%.

My bike is very special and the extra 10 cents a gallon in a three-gallon tank isn't worth the time spent trying to work out what I could do with the 30 cents saved buying cheaper stuff. Beats me that folks will spend $1000s on exhausts, Freeks, chrome, Corbins etc. and then worry about 10 cents on a gallon.

Chill, folks. If you're good to her, she's good to you. Go ahead, spend that extra 10 cents.

Siggy

I use only the top shelf stuff. My senitments echo those of "Sigmund" and I never, ever use any gas containing ethonal. The creme/green develops a hesitation trying to burn corn !

Sorry Siggy, I've been putting 89 Octane in mine (both straight gas and ethanol blend) since day one, and have 23000 miles of flawless running on it. I still get 43 mpg as well pretty much consistently around town or on the open highway (maybe a few mpg more with steady highway cruising). Last time I looked in my carb throats they were just fine. And, now there is a local station pumping 89 octane Ethanol blend for what the other stations are charging for 87 Octane normal gas, so you're darn straight I'm going to take a 20cent/gal price savings. The more money I save on gas, the farther I can ride since I am not on an unlimited budget, and since our friends in the oil business continue the creep back up to $3 a gallon with nary a protest....

Quote:

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Sorry Siggy, I've been putting 89 Octane in mine (both straight gas and ethanol blend) since day one

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Ah, perhaps I should be clearer - the "10 cents" is in realtion to the 87 Octane; I, too, have been running 89 Octane as the manual suggests.

And so far the general "suggestions" leave me no wiser! Some of us say 87's OK, others say no, some say it depends whose gas you buy... so I'll stay with the manual's suggestion on the basis that the makers of the bike think that's a good idea.

Siggy

The higher octane fuel is best utilized by the higher compression engines - it resists pre-detonation better, therefore reducing knock or ping, as stated earlier.

It's almost like the LOWER octane fuels are HOTTER fuels - they are more apt to "auto-ignite" in a high compression engine, like Matt said. Our engines are high compression, just not that high. I'm guessing anything higher than a 10:1 compression ration would dictate higher octane fuel.

I know this basically pertains to the bikes but my lexus Shows (on the miles left to drive gauge) and addittional 83 miles per tankfull when using premium

This is an article I found on the internet....

In many high-performance situations, riders clamor for higher octane fuels, thinking this will give them additional horsepower and, thus, an advantage over the competition. But this is not the case-adding higher-octane race fuel to your motorcycle may actually produce less horsepower. Here's why: Octane, an arbitrary number which is calculated as the average the Research Octane Number (RON) and the Motor Octane Number (MON), and is only an indication of a fuel's sensitivity to knock, which is typically pressure-induced self-ignition. (Of these two ratings, MON is more applicable to racing fuels as it is measured under high load and high speed conditions.)

Octane, as you can see, is not a measure of how much power - or, more correctly, specific energy - is contained in a fuel. And remember that leaded high-octane race fuels burn slower than most unleaded fuels, and may reduce performance in stock or lightly modified motorcycles. A high octane rating itself, however, does not mean that the fuel is slow burning. Hence, it has no direct bearing on the power characteristics of the fuel.

The knock tendency (and hence, the Octane rating) of a fuel is a function of the amount of free radicals present in the fuel prior to ignition and can be reduced by the addition of tetra ethyl lead, aromatics and other additives.

Although some racing organizations still use maximum octane number as the discriminating factor for fuel legality, it is really not appropriate for racing purposes.

Instead one should look at the amount of energy (heat) released in the burning of a particular fuel. This is described by the specific energy of the fuel. This quantity describes the amount of power one can obtain from the fuel much more accurately. The specific energy of the fuel is the product of the lower heating value (LHV) of the fuel and molecular weight of air (MW) divided by the air-fuel ratio (AF):

Specific Energy = LHV*MW/AF

For example, for gasoline LHV= 43 MJ/kg and AF=14.6, while for methanol LHV= 21.1 MJ/kg (less "heat" than gasoline) and AF=6.46 (much richer jetting than gasoline). Using the above formula we see that methanol only has a 10% higher specific energy than gasoline! This means that the power increase obtained by running methanol, with no other changes except jetting, is only 10%. Comparing the specific energy of racing and premium pump gas you can see that there is not much, if any, difference. Only alcohol s (such as methanol or ethanol) have a slightly higher specific energy than racing or pump gas.

Other oxygen-bearing fuels, besides the alcohols and nitromethanes, such as the new EL fuel, will also produce slightly more power once the bike is rejetted. However, at $15.00 to $20.00 at gallon for the fuel the reportedly minor (1 % - 2%) improvement is hardly worth the cost for the average racer.

The real advantage of racing gasolines comes from the fact that they will tolerate higher compression ratios (due to their higher octane rating) and thus indirectly will produce more power since you can now build an engine with a higher compression ratio. Also, alcohols burn cooler than gasoline, meaning even higher compression ratios are possible with them, for even more power.

The bottom line here is that, in a given engine, a fuel that doesn't knock will produce the same power as most expensive racing gasolines.

However, it sometimes happens that when you use another fuel, the engine suddenly seems to run better. The reasons for this are indirect: First, the jetting may be more closely matched to the new fuel. Secondly, the new fuel may improve the volumetric efficiency (that is, the "breathing") of the motor. This happens as follows: Basically a fuel that quickly evaporates upon contact with the hot cylinder wall and piston crown will create additional pressure inside the cylinder, which will reduce the amount of fresh air/fuel mix taken in. This important-but often overlooked-factor is described by the amount of heat required to vaporize the fuel, described by the 'enthalpy of vaporization' (H), or 'heat of vaporization' of the fuel.

A high value of H will improve engine breathing, but the catch is that it leads to a different operating temperature within the engine. This is most important with two-strokes, which rely on the incoming fuel/air mix to do much of the cooling-even modern water-cooled two-strokes rely on incoming charge to cool the piston. For two-strokes a fuel that vaporizes, drawing a maximum amount of heat from the engine, is essential-the small variations in horsepower produced by different fuels is only of secondary concern.

Also important is the flame speed: Power is maximized the faster the fuel burns because the combustion pressure rises more quickly and can do more useful work on the piston. Flame speed is typically between 35 and 50 cm/sec. This is rather low compared to the speed of sound, at which pressure waves travel, or even the average piston speed. It is important to note that the flame propagation is greatly enhanced by turbulence (as in a motor with a squish band combustion chamber).

The most amazing thing about all this is that you can get the relevant information from mc racing gasoline manufacturers. Then, just look at the specification sheet to see what fuel suits you best: Hot running motors and 2-strokes should use fuels with a value of "H" that improves their cooling, while more power (and more heat) is obtained from fuels with a high specific energy.

By the way, pump gas has specific energies which are no better or worse than most racing gasolines. The power obtained from pump gas is therefore often identical to that of racing fuels, and the only reason to run racing fuels would be detonation problems, or, since racing fuels are often more consistent than pump gas - which racers call "chemical soup."

Let's make it clear, octane rating is not a measure of the quality of the fuel, it is an indication of how easily it ignites and burns. There is no particular advantage to using gat rated at a higher octane than needed, but there can be some long term disadvantages.
1. The slower ingiting properties can change the effective ignition timing. On modern bikes, you can't just loosen a bolt or 2 screws and give it a little more advance, so it could cost you a little power.
2. Slower burn can result in the fire quenching before all the fuel is fully burnt, causing carbon buildup. With heavy carbon deposits, you get hot spots that will ignite the mixture if you don't continue using high octane fuel.
3. Although it's more of a problem on the high reving smallbore multicylinder bikes, (remember that little 175 Honda that was advertized to turn something like 1700? Ever wonder why they dropped that line like a hot potato?) slower burning fuel means more heat later in the cycle, possibly enough to shorten exhaust valve life.

Triumph mechanic told me that in motors he has tore apart the ones that the owner used premium grade gas (93 octane) had lots more carbon deposits than ones where the owner had used mid grade(89 octane)