Octane for Ducs

[jk750]

Someone posted in General a pdf of their owners manual, and it clearly stated running minumum 95 fuel octane gasoline.

I know that's not the US standard (R+M)/2 octane rating we use, but simply the Italian RON rating.
This should be cleared up in U.S. versions of the manual, but apparently it's not.

What do you Duc owners put in your tanks???

[Ducboy]

Originally Posted by jk750

What do you Duc owners put in your tanks???

Take this fwiw, but as a long time owner of a 96 SBK and on 01 ST4 I feed them 89. I've used 92/3 with no noticable difference. Many discussions about this on other Duc boards and amongst the educated contingent 89 - even 87 - works fine with no detriment to your machine. I'm no expert on octane but there it is.

I'm not sure what my manuals say though I believe it's generally accepted to use the min your manual states.

[jswledhed]

I run 89 or 93 in my M750. Though, I have read online many times that the air-cooled engines actually run better with 87-89. I've tried all three, but can't really find much of a difference in performance or mileage between any of the three.

[bzbatl]

That pdf link is basically the same as my hardcopy manual I have. There's a few updates in it, since it's a 2006 manual, but it also has the 95 octane gibberish in it. Ducati should really do something about that.

I put 87 in my 800SS this weekend, and didn't notice any ping for 100+ miles of riding. The guys at the downtown Ducati shop swear by using 87 in everything (even their track machines) and say nothing bad comes about using 87 as long as you ride it often. Guess settling gas gives it problems... maybe?

[Blackduc]

I used to put 92/93 in and never had problems.

[749er]

93 octane- Shell or Exxon.

[KRG]

92-94 Octane is what I run in my 04 749. I have run lower grade as well (in a pinch) and like everyone else has said, I didn't notice any mileage, power, or performance differences.

Now race gas... THAT is something else entirely... muhahahaha!!

Cheers!

[jk750]

I love the smell of race gas in the morning. Smells like... victory.

I really do.

[F27Corsair]

Just came about this thread and thought i'd add my input. In the owners manual, it says to use 95-98 RON. RON is the measurable octane rating in Europe. In the USA and Canada, we use PON. PON has a 4-5 point lower equality rating than RON. So...

95 RON (europe) is the same as 91 PON (N. America). Got it?

Now, for those of you that expect to see greater performance out of higher octane, well you guys just wont see it. Thats not what higher octane does. It prevents pre-detonation, also referred to as knock. And just because some of you dont hear a noticeable knocking sound doesnt mean you dont do damage to your engine. Can you probably get away with a lower octane if you dont run your bike hard? Certainly. But if you are a spirited rider, and your owners manual says to use high octane in your bike, i highly suggest you use it.

[Ducman851]

Just a little lite reading for ya.

In many high-performance situation, 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 of the Research Octane Number (RON) and the Motor Octane Number (MON), and is only an indic ation 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= 21.1MJ/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 g asoline! 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 ELF 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 rati o. 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 e fficiency (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 mode rn 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 second ary 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 most 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 wit h 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 probl ems, or, since racing fuels are often more consistent than pump gas--which racers call "chemical soup"--a consistent reading of the spark plugs and exhaust pipe.