View Full Version : 1987 883 Sportster - Which Fuel Grade?

Brad Harris
2nd August 2007, 02:39

I just bought this bike and would appreciate knowing what octane fuel it requires.

Thanks very much,


2nd August 2007, 05:29
Service manual states 89 octane or higher. Also welcome to the forum.

2nd August 2007, 06:15
Welcome, and I put nothing but premium 92 or better in Ol' Betty, my '89 XLH.

2nd August 2007, 08:17
IF an engine is designed for an octane of 89 that should work fine the 92 should work "almost" as well BUT if you think PREMIUM is better gas than regular than the Advertisement Communitiy is doing one hell of a good job. There are good reasons to use high octane fuel, being better gas is NOT one of them, but I always enjoy this thread.:shhhh

Bottom line, high compression engines require higher octane fuel to perfrom as designed. So the simple question remains is your engine high compression? It's my understanding that stock XL883 made before 2007 are NOT high compression engines and designed to run on fuel that has an octane rating of 89

2nd August 2007, 12:09
Use the lowest grade possible that allows the engine to operate without pinging. (please pardon my dangling participle)

2nd August 2007, 15:09
The easy answer is to take what everyone has said in this thread so far, and amalgamate it. The bike is designed for 89 octane, but as Rikrak said, higher compression engines may require a higher octane rating.

Since you mentioned that you just bought the bike, there is a strong possibility that the previous owner has made some modifications of one type or another to it; Harley owners (and especially us Sporty folk) are notorious for taking the phrase "stock sucks" as doctrine. So, you go to the pump and drop in some 89 octane. Go for a ride with it and listen to the engine. If you hear pinging, at the next fill-up, use 91 (or whatever the next lowest octane available in your area is). Repeat process, increasing octane each time, until pinging stops. At that point, you'll know what octane to use! Simple 'nuff.

It may not be a great scientific answer, but it will work. Given that you'll probably be doing a LOT of riding on it now, going through a tank of gas will be nothing; you'll do that in a few days (if not less), so you'll probably know within a week what octane works for your bike.

One thing to watch for when using this procedure is where you fill up. As many places nowadays have one nozzle/hose that connects to all three tanks, the first few liters (pronounced "gallons" for you Yanks) are going to be from the previous guy's fill-up. A buddy who worked at a gas station informed me that the first 3-4 liters (roughly 1 gallon) will be what's left in the lines from before. Now, for a car holding 20-30 gallons, that's nothing. But for a bike that only holds 3.3 gallons at most, that's a large percentage at an unknown octane. Point being, when possible, try to fill up at a place that has separate hoses for each (or at least has a separate one for the premium).

That being said, I tend to use 91/92 octane when possible. I find it's a little smoother at idle.

On an unrelated note, welcome to the forum! :welcome

2nd August 2007, 16:11
Welcome to the XL Forum, I also use premium whenever I can!

3rd August 2007, 23:16
I used to try 87 octane for a few tanks, but definately not performing like it should, so I usually stick with 91 now. I could probably use 89, but figured the 'ole girl is running fine with 91 so why bother for a few cents difference. Welcome too!

4th August 2007, 03:38
My 87 says 89 or higher on the sticker on the right hand downtube.
Hope this helps

5th August 2007, 20:14
IF an engine is designed for an octane of 89 that should work fine the 92 should work "almost" as well BUT if you think PREMIUM is better gas than regular than the Advertisement Communitiy is doing one hell of a good job. There are good reasons to use high octane fuel, being better gas is NOT one of them, but I always enjoy this thread.:shhhh

Bottom line, high compression engines require higher octane fuel to perfrom as designed. So the simple question remains is your engine high compression? It's my understanding that stock XL883 made before 2007 are NOT high compression engines and designed to run on fuel that has an octane rating of 89

doesn't the H in the XLH stand for High compression? if not what does it stand for?

5th August 2007, 20:37

I just bought this bike and would appreciate knowing what octane fuel it requires.

Thanks very much,

BH I have a 2004 Rubbermount which is supposed to use regular (87 octane). It doesnt run good on regular. Bad gas mileage, more engine noise, and rougher running. I run 93 octane all the time and it runs great. I dont care what you self proclaimed "gas experts" say, all my bikes ALWAYS run better on high test gas and I have been riding for 40+ years. If octane makes no difference why do engines make more power on NITRO and NOS with no other changes????? Also, if running the lowest octane possible is best for your engine, should I run diesel fuel all the time in my BMW (motorcycle). The gas pump was messed up and pumped a whole tank of diesel into my BMW tank. It ran, would cruise at 85 mph, but it smoked a little on acceleration. It got pretty good mileage though, about 50 mpg. Somehow I dont think it was real good for my engine. Whatdoya think.......Dew.

6th August 2007, 10:58
Just having finished reading the MSN article on how Americans spent 15 BILLION on bottled water last year and knowing less about gas myself I tend to just read what others say. I've only been riding 37 years and yes, in High School the common thought was to fill your old clunker with Premium and "blow it out" on the highway. Now there is, according to this article "some" reasons why premium fuel gets better milage. However, marketing is a powerful tool in America and all I can say is when I use Regular, Mid-Grade or Premium in my "plain Jane" XL883 (2005) I really can't tell any difference at all so if it's a ONE nozzle all three grade pump I'm using "Regular" for sure. Maybe others can really feel a difference, for grins I've tried them all never could tell any difference so as long as it says 89 octane that's what I get.

Octane rating
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A gas station pump offering five different octane ratings.The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines. It is a measure of anti-detonation of a gasoline or fuel.

Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. [1]

Contents [hide]
1 Definition of octane rating
1.1 Measurement methods
2 Examples of octane ratings
3 Effects of octane rating
4 Regional variations
5 References
6 External links

[edit] Definition of octane rating
Octane is measured relative to a mixture of iso-octane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline, for example, has the same octane rating as a mixture of 87% (by volume) iso-octane and 13% (by volume) n-heptane. This does not mean, however, that the gasoline actually should contain these chemicals in these proportions. It simply means that it has the same autoignition resistance as the described mixture.

A high tendency to autoignite, or low octane rating, is undesirable in a gasoline engine but desirable in a diesel engine. The standard for the combustion quality of diesel fuel is the cetane number. A diesel fuel with a high cetane number has a high tendency to autoignite, as is preferred.

[edit] Measurement methods
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.[citation needed]

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, straight ethanol, AvGas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116). Typical "octane booster" additives include tetra-ethyl lead and toluene. Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition. This is why leaded gasoline has a higher octane rating than unleaded.

[edit] Examples of octane ratings
The octane ratings of n-heptane and iso-octane are respectively exactly 0 and 100, by definition. For some other hydrocarbons, the following table[2][3] gives the road octane numbers.

n-octane -10
n-heptane 0
2-methylheptane 23
n-hexane 25
2-methylhexane 44
1-heptene 60
n-pentane 62
1-pentene 84
n-butane 91
cyclohexane 97
iso-octane 100
benzene 101
E85 Ethanol 105
Methane 107
Ethane 108
Toluene 114
Xylene 117

[edit] Effects of octane rating
Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression ratio only governs the maximum compression that can be achieved).

Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitues the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Octane rating is a measure of detonation resistance, not deflagration characteristics.

It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre[citation needed] due to the composition of the fuel as well as increased octane.

A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content on a volume basis (per litre or per gallon). The reason for this is that ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl radical for a H hydrogen which transforms the gas ethane (C2H6) into ethanol. Note that to a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

In the case of alcohol fuels, like Methanol and Ethanol, since they are partially oxidized fuels they need to be run at much richer mixtures than gasoline. As a consequence the total volume of fuel burned per cycle counter balances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred max power air fuel mixture of 12.5:1, it will release approximately 19,000 BTU (about 20 MJ) of energy, where ethanol run at its preferred max power mixture of 6.5:1 will liberate approximately 24,400 BTU (25.7 MJ), and Methanol at a 4.5:1 AFR liberates about 27,650 BTU (29.1 MJ).

To account for these differences, a measure called the fuel's specific energy is sometimes used. It is defined as the energy released per air fuel ratio. For the case of gasoline compared to the alcohol fuels the specific energies are as follows:

Fuel Net energy Units
Gasoline 2.92 MJ/kg
Ethanol 3.00 MJ/kg
Methanol 3.08 MJ/kg

Using a fuel with a higher octane lets an engine run at a higher compression without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure, which is a function of elevation and weather conditions.

Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine power is a function of the fuel as well as the engine design and is related to octane ratings of the fuel... power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved.

Many high-performance engines are designed to operate with a high maximum compression and thus need a high quality (high energy) fuel usually associated with high octane numbers and thus demand high-octane premium gasoline.

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is false—engines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal or even imaginary.

Using high octane fuel for an engine makes a difference when the engine is producing its maximum power. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. Depending on the engine design, this particular circumstance can be anywhere along the RPM range, but is usually easy to pin-point if you can examine a print-out of the power-output (torque values) of an engine. On a typical high-revving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder; although the cylinder is already rising at the time the intake valve closes, the forward speed of the charge coming into the cylinder is high enough to continue to load the air-fuel mixture in.

When this occurs, if a fuel with below recommended octane is used, then the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a white paper that gives an example: [1] . In this example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load then the difference in octane will have even less effect. The example cited does not indicate at what elevation the test is being conducted or what the barometric pressure is. For each 1000 feet of altitude the atmospheric pressure will drop by a little less than 1 inHg (11 kPa/km). An engine that might require 93 octane at sea level may perform at maximum on a fuel rated at 91 octane if the elevation is over, say, 1000 feet. See also the APC article.

The octane rating was developed by the chemist Russell Marker. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.

[edit] Regional variations
Octane ratings can vary greatly from region to region. For example, the minimum octane rating available in much of the United States is 87 AKI and the highest is 93. In the Rocky Mountain (high altitude) states, 85 octane is the minimum octane and 91 is the maximum octane available in fuel. The reason for this is that in higher-altitude areas, a typical combustion engine draws in less air per cycle due to the reduced density of the atmosphere. This directly translates to reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill up a car with a carburettor that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine. In some east coast states, up to 94 AKI is available [2]. In parts of the Midwest (primarily Minnesota, Illinois and Missouri) ethanol based E-85 fuel with 105 AKI is available [3].

California fuel stations will offer 87, 89, and 91 octane fuels, and at some stations, 100 or higher octane, sold as racing fuel. Up until 2003 or 2004, 92 octane was offered in place of 91.

In many parts of Europe, 95 RON (90-91 AKI) is the minimum available and the standard, with 97/98 being premium or "super". In Australia, "regular" unleaded fuel is RON 91, "premium" unleaded with RON 95 is widely available, and RON 98 fuel is also reasonably common. Shell sells RON 100 petrol from a small number of service stations and most of which are located in capital cities. In other countries "regular" unleaded gasoline, when still available, is sometimes as low as 85 RON (still with the more regular fuel - 95 - and premium around 98 available.) In Russia and CIS countries 80 RON (76 AKI) is the minimum available and the standard.

[edit] References
^ Page 992. Brown, Theodore, and LeMay, Eugene, et. al. Chemistry: The Central Science. Ninth edition. Pearson Education Inc. Upper Saddle River, NJ. 2003. ISBN 0-13-066997-0.
^ http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/coal.html
^ http://www.iupac.org/publications/pac/1983/pdf/5502x0199.pdf

[edit] External links
Octane ratings of some hydrocarbons

Petroleum and Coal
Gasoline Refining and Testing
Information in general

Gasoline FAQ
How Octane Works at HowStuffWorks.com
Khoo, Kenny K. Understanding Octane and its Related Components.Yellowknife: Smithsonian Press, 2006.

Retrieved from "http://en.wikipedia.org/wiki/Octane_rating"

16th August 2007, 01:50
I use 93 because I figured it's an air cooled engine and running temps could get pretty high, which usually causes detonation on lower octane fuel.

16th August 2007, 02:29

I just bought this bike and would appreciate knowing what octane fuel it requires.

Thanks very much,


Always use the lowest grade your bike is ok with....

Lower octane fuel burns faster, and leaves fewer deposits....modifications may make a higher octane necessary, but you will do no damage with the minimum octane the manufacturer suggests in a more or less stock bike....

Personally, I use mid-grade (89 octane) on my 97...converted to 1200 with 10:1 compression....she's fine with it...