Gas Type

[Lee]

Ok, now this may be a stupid question, and yeah, I am a newb (First bike and all...) however, I've searched the site and I can't find what octane level the fuel for an XS should be. My bike is a salvage project so I have no manual for the bike, also, we may have different types of gas in Canada than the States (pollution laws and so forth). Does it matter, and does anyone know what the manual recommends?

Cheers,
Lee

[John]

Before I did the big bore on mine I could use mid grade with no pinging. Now I have to use premium, but with only a 3.9 gal tank, the difference between mid grade and premium is only about $.40 per tankful.

[Pat Kelly]

I've used all 3 grades on my (mostly) stock XS's and I find no difference. I use regular unleaded, 87 octane.

[TopCatGr58]

Probably more than you want to know!

The manual says "REGULAR" fuel. After some research into Octane, found some interesting info. In early 70's the US mandated an averaging of the 2 common ways of rating octane, the Research Octane Number and the Motor Octane Number
(R+M)/2 = octane. The Motor octane number can be as much as 10 points lower than the Research #. In the below info, for engines with certain compression ratios, ie. 9.0:1, an octane of
96 is suggested, but the Gasoline FAQ this came from didn't specify whether this was a RON or MON value. Still, if it was an RON, and at the most a MON would be 86, that would stilll give you an average (R+M)/2 value of 90. That's still the MEDIUM grade in most states. I, too, have the Big Bore kit and we now have Comp ratios closer to 10.25:1, using same formula for a suggested octane(RON) of 100 would get us to 95! 93 is about the highest we can find, and as the below info states, KNOCKING is not good and can destroy an engine!

So....its' suggested that you try the lower octane, but IF you get any knocking, you quickly add a higher and then continue to use a higher Octane fuel so that you do NOT experience any knocking!

Excerpts from the Gasoline FAQ!

6.2 Why do we need Octane Ratings?

To obtain the maximum energy from the gasoline, the compressed fuel-air mixture inside the combustion chamber needs to burn evenly, propagating out from the spark plug until all the fuel is consumed. This would deliver an optimum power stroke. In real life, a series of pre-flame reactions will occur in the unburnt "end gases" in the combustion chamber before the flame
front arrives. If these reactions form molecules or species that can autoignite before the flame front arrives, knock will occur [21,22].

Simply put, the octane rating of the fuel reflects the ability of the
unburnt end gases to resist spontaneous autoignition under the engine testconditions used. If autoignition occurs, it results in an extremely rapid pressure rise, as both the desired spark-initiated flame front, and the undesired autoignited end gas flames are expanding. The combined pressure peak arrives slightly ahead of the normal operating pressure peak, leading to a loss of power and eventual overheating. The end gas pressure waves are
superimposed on the main pressure wave, leading to a sawtooth pattern of pressure oscillations that create the "knocking" sound.

The combination of intense pressure waves and overheating can induce piston failure in a few minutes. Knock and preignition are both favoured by high temperatures, so one may lead to the other. Under high-speed conditions knock can lead to preignition, which then accelerates engine destruction

6.13 Can higher octane fuels give me more power?

On modern engines with sophisticated engine management systems, the engine can operate efficiently on fuels of a wider range of octane rating, but there remains an optimum octane for the engine under specific driving conditions.
Older cars without such systems are more restricted in their choice of fuel, as the engine can not automatically adjust to accommodate lower octane fuel.
Because knock is so destructive, owners of older cars must use fuel that will not knock under the most demanding conditions they encounter, and must continue to use that fuel, even if they only occasionally require the octane.

7.2 What is the effect of Compression ratio?

Most people know that an increase in Compression Ratio will require an increase in fuel octane for the same engine design. Increasing the compression ratio increases the theoretical thermodynamic efficiency of an engine according to the standard equation

Efficiency = 1 - (1/compression ratio)^gamma-1

where gamma = ratio of specific heats at constant pressure and constant volume of the working fluid ( for most purposes air is the working fluid, and is treated as an ideal gas ). There are indications that thermal efficiency reaches a maximum at a compression ratio of about 17:1 for gasoline fuels in an SI engine [23].

The efficiency gains are best when the engine is at incipient knock, that's why knock sensors ( actually vibration sensors ) are used. Low compression ratio engines are less efficient because they can not deliver as much of the ideal combustion power to the flywheel. For a typical carburetted engine, without engine management [27,38]:-

Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

Modern engines have improved significantly on this, and the changing fuel specifications and engine design should see more improvements, but significant gains may have to await improved engine materials and fuels.

7.6 What is the effect of temperature and load?

Increasing the engine temperature, particularly the air-fuel charge temperature, increases the tendency to knock. The Sensitivity of a fuel can indicate how it is affected by charge temperature variations. Increasing load increases both the engine temperature, and the end-gas pressure, thus
the likelihood of knock increases as load increases. Increasing the water jacket temperature from 71C to 82C, increases the (R+M)/2 ONR by two.

7.8 What is the effect of engine deposits?

A new engine may only require a fuel of 6-9 octane numbers lower than the same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to the formation of a mixture of organic and inorganic deposits resulting from both the fuel and the lubricant. They reach an equilibrium amount because
of flaking, however dramatic changes in driving styles can also result in dramatic changes of the equilibrium position. When the engine starts to burn more oil, the octane requirement can increase again. ORIs up to 12 are not uncommon, depending on driving style [27,28,32,111]. The deposits produce
the ORI by several mechanisms:-
- they reduce the combustion chamber volume, effectively increasing the compression ratio.
- they also reduce thermal conductivity, thus increasing the combustion chamber temperatures.
- they catalyse undesirable pre-flame reactions that produce end gases with low autoignition temperatures.
************************************************** **
From Columbia Encyclopedia:
At present three systems of octane rating are used in the United States. Two of these, the research octane and motor octane numbers, are determined by burning the gasoline in an engine under different, but specified, conditions. Usually the motor octane number is lower than the research octane. The third octane rating, which federal regulations require on commercial gasoline pumps, is an average of research octane and motor octane. Under this system a regular grade gasoline has an octane number of about 87 and a premium grade of about 93. Most American-made cars that were built in the 1971 model year or later can use regular gasoline. To prevent knocking, premium grade gasoline must be used in many cars built before 1971 and in some new cars that have high-performance engines.

[mason79]

oh my

dam tc, don't be so modest sometimes, you have a right never to be

[Ken Talbot]

Hey, Lee, where abouts on the Island are you? I'm guessing Victoria, but Nanaimo might not be out of the question. There are a few XSives on the Island, including at least one ex-Xsive right in Victoria and another XSive out at Sooke. Sid is at Ladysmith, Courtney is at Nanaimo, Skinnybiker is in Courtenay, Glen is in Port Alberni, and there's at least one or two more.

BTW - all I've ever used in my fleet is Regular.....

[MAXIMAN]

All I usually run in mine is 89. It has never "pinged" and as a matter of fact seems to get worse gas mileage with higher grades (91 or 93).

I really can't imagine that a stock Eleven with 9.25 or 9.0 compression would ever need any more than a mid grade fuel. My 2005 ZRX1200R has 10.1:1 ratio and an ingition curve advanced far more than the XS11. Kawasaki recommends RON of 91.

However in a few weeks Godzilla will be getting a complete overhaul to included a Big Bore, cams, head works, header, and the whole nine yards. I'm certain after this little upgrade he will require high octane fuel.

[ElCid]

I discovered on a trip to Cape Breton that I get significantly better mileage running the highest available octane in my 79 special. While running returning home from northern Quebec, I ran the interstate for several tanks full and felt fairly confident in my results. As someone who's just getting warmed up at 100 miles, I think the extra 10-15 miles per tank is worth it, but I never had any problems running the mid grade. This was prior to the installation of the 1173 kit and the work on the heads.

[Lee]

Further North...

Hey Ken,

I'm in Campbell River, the former salmon capital of the world, hehe. It's about a half hour north of Courtney and about the same size.

[yamarider]

My advice is to ensure that your carbs are clean and tuned correctly. Then experiment with diffenent octane ratings and note how your bike performs. Although the original manuals recommend 91 octane, the truth is that today individual regions add diferent stuff to fuel at various times of the year which affects performance.

[bandet01]

i only run the highest i can find at the gas station i am at and the reason i do that is to keep the inside of the engioen cleaner and once in a while i will put 3 gallons of race fuel in it but i have found it does run better on the high octane stuff better then the cheap stuff and for a extra 1.00 at the most it is worth it in my mind

[webbcraft2150]

The sticker under my seat says to use a fuel with a 93 octane rating. When I still lived in Albuquerque, I could get away with using regular fuel during the winter. Since Austin dosen't have a "real" winter, I keep pumpin the high dollar stuff to keep the pingin at bay. With fuel prices what they are, another option is octane booster. I found about 3-4oz. in a full tank works well when using the lower grade fuels. I dont worry much about fillin the bike with the high $ stuff. If you do the math, its not alot more money when fillin up with 3-4 gallons. Its a whole different story when fillin the truck with a 25gal main and 2, 18gal saddle tanks @8-10mpg. Or the boat @45gals and 2-3mpg. Moral to the story, if it runs good on the cheaper stuff, use it, if it dosen't buy the good stuff, these bikes deserve to be pampered.

[TADracer]

Ditto ElCid. My 79 special seems to run better on 93 octane and get better mileage too. But even on 87, I do not get any pinging.

Could this be because of the different cams in the early bikes?

[sxigh]

appears that the stories vary too much for there to be any great consensus. I say run 87 unless its absolutely necessary. lower octanes get purchased more frequently than higher octanes and at a 4-6 wk shelf life, I'd be more worried about poor ignition when buying 93 octane than anything else. the guys at motorcycle performance here in madison put it pretty well, so read on: http://www.motorcycleperf.com/tectip.htm

[AKMac]

Just a thought, but I can get 100 Low Lead for free. I think I should experiment with some. Would there be any side effects to running leaded fuel?