ducatipaso.org

Hello all,

Just looking for advice as to which grade and type fuel should be used in a Paso 906. Is 88 ok or should I go with higher octane, like 91? I am in the U.S. Since we only have unleaded fuel, I need advice from owners.

Thanks in advance.

87 should be fine to use unless you hear pinging or knocking.

Some more info: http://www.desmoducati.org/octane.html

Very strange, that You usa guys have very low octane Here in EU area we use NORMALLY 95 and if want "little better", then we choose 98.

Finn Paso is onto it, 95 minimum, got a 907 myself but have seen other sites saying for these motors run Premium [95] (as it is branded here in Oz) Even my 900 bevel likes the higher octane better , (9.5 comp ratio) ,comparable to the 904 motor, You won't hurt it by trying , give it a go and post results. [All care taken but no responsibility accepted,] Quote from my lawyer before I went to jail,............. Happy destinations with your detonations, Marty

Octane ratings in the US are different than in the UK or EC or about anywhere else in the world - we take the average of RON and MON which basically means our numbers come out roughly 5 lower than the rest of the world.

So... if 95 is stated for Europe, in the USA 90 would work just fine.

FWIW I put 91 or higher in my 907 just because. Would probably run fine on 89 but the extra $0.50 per tank it costs doesn't bother me. As for people who get stressed about using too high of an octane rating, on pump gas it doesn't matter. 91 or 92 or 93 won't hurt anything even if you could get away with 89.

Truly thanks to all of you for your input. Much appreciated. It's nice to see tha there is still somewhat of a community and enthusiasts left.

My '89 906,with the original weber,"works" with 95,but "runs" with 98...much to my dislike,because of the price of the latest.But there is a hell of a diference.Anyway,it could be only in mine,and the others would work fine on 95.
Hasta la vista

For me, when in doubt, start with the highest octane, then drop down to mid level and evaluate. If you get pinging and pre-spark ignition (knocking), then you have to go back up in octane. The knocking is the easiest to make present when taking off from a standstill or when nailing the throttle at a fairly low rpm. If you don't get the knocking with mid-grade, you can try the low-grade. Always try to run one grade higher than the gas that gave you the knocking/pinging.

With my Harley, it really needs to run high-octane with the mods that are done to it. I run mid-grade, though, because I don't notice any difference in mileage. If I put the engine under heavy load, I will get knocking, but if I let off on the throttle a little, it goes away. Since it is my daily commuter, I can get away with this. With the Ducatis, I couldn't get away with it because I'm always flogging them. I generally run high-test with the Ducatis. Sometimes in the mountains, the little mom-and-pop gas stations may have questionable gas where octane and quality are concerned, so I would rather run high-test and be *safer*, than get a batch of gas that the bike just really doesn't like.

I hope this helps.

wow my second post thats cool i run my paso on nonoxy gas i live in minnesota so i dont know if they have that where you live all i can say is this when i first got the bike i put 92 octane from bp and it still sputtered from the alchohal in the gas now that i am using nonoxy fuel in the bike it runs perfect even in stoplight to stoplight traffic in 90 degree weather i know the pasos have had problems with inner city traffic but since using the nonoxy gas i have not experienced any of these traits it runs like a champ the non oxygenated gas here in minnesota is rated 91 octane the downside is that it is not sold at every station here i am limited to where i can fuel up if you have access to this kind of fuel i highly recommend it if there is and old car club or similar they may have a listing of gas stations that carry nonoxy fuel in your area in minnesota go to msra.com

Not to be contrary,but you all have it reversed. You should start with the lowest octane gas and work your way up to avoid pinging. Here in Pennsylvania I find the mid grade(89) works well on most brands for all seasons. Here we have lots of rolling hills and flat roads are few and far between and every driver feels it is their god given right to drive at 80mph.. Low octane(87) here tends to induce pinging on hard acceleration due to the positive grades on most roads. If you live in a flat area in the US 87 is all you should need. There is absolutely no reason to use a higher octane in an engine with compression less than 10.5. High octane gas burns slower(cooler) than low octane gas. This usually means if you use high octane in an engine designed for lower octane you risk idle problems,hesitation issues and shorter engine life due to carbon build up and accumulation. In a Ducati that means shorter valve/guide life and ring issues and if you still have a carb it will make getting the proper jetting that much harder to achieve.

Higgy is right on. The lower the octane the better.

higgy wrote:Not to be contrary,but you all have it reversed. You should start with the lowest octane gas and work your way up to avoid pinging.

I guess this would depend on what the bike is and whether it had any engine modifications. Following your lowest-to-highest advise would have required me dumping out a tank of gas in my Harley if I started with 87 octane. In that situation, though, I knew I'd have to run a higher octane because I had the heads modified and changed the camshaft. I'm pushing it running 89 octane and have to be careful with the throttle when starting from take-offs or when at lower rpm on inclines.....with gas prices dropping, I'm back up to 93 octane in this bike.

The newer, stock Ducatis have 95 RON recommended in the manual. In the US, that's 91 octane, if memory serves me correctly. This means starting off with 92 or 93 octane (US). It appears I can safely run 87 in these newer Ducs, but I generally try to stay at 89 or higher because most of the stations around here are slapping ethanol in their gas, and I'd hate to get a batch of 87 that plays havoc. Nothing like spark-knocking while riding in the mountain twisties at a spirited pace.

higgy wrote: High octane gas burns slower(cooler) than low octane gas. This usually means if you use high octane in an engine designed for lower octane you risk idle problems,hesitation issues and shorter engine life due to carbon build up and accumulation.

That is a myth - Higher octane gas does NOT burn slower than lower octane gas. If it did, detonation would get WORSE when you used it, not better. In any case, higher octane gas doesn't use flame speed to deal with detonation anyway. Higher octane gas is more resistant to auto-ignition; it withstands high temps and pressures longer than lower octane gas. (FWIW Higher octane gas doesn't burn faster than lower octane either - their flame front speeds are virtually same - everything else being equal, which it rarely is)

Normal combustion has a flame front(s). Detonation is an explosion. No flame front. BOOM. All the unburnt mixture goes at once, flame or no flame. There are pictures of this out there. The "knock" you here is the shock wave from the explosion bouncing around in the cylinder.

Any mixture will explode after a certain amount of time at the temps and pressures in a cylinder. The higher the temp and or pressure, the faster it explodes. This amount of time before this happens is sometimes called the delay period. If you can burn the mixture before the delay period is up, there is no detonation. If the delay period runs out before the mixture is burned, the unburned portion explodes, causing detonation.

With a given temp and pressure, there are two ways to lessen the tendancy to detonate. You can burn the mix faster, or you can increase the delay period. Higher otane gas increases the delay period. Dual plugs and swirl in the intake charge burn the mix faster. There is no way burning anything slower will help. Think about it. How many mods are out there promising "more complete combustion". More complete. In the same amount of time. Hard to do that without burning the mixture faster.

pure bullshit,You are confused. Boyles law rules. pvt1 = pvt2 period. Increasing the temperature or the pressure on the fuel makes it burn faster( at a higher flame propagation)Detonation or its cousin pinging is as you state due to instant combustion brought on by either higher pressure or higher temperature than the octane of the fuel is rated for.Detonation is way to fast burning,charge ignites while the piston is still moving up btdc,all at once,pinging is too fast burning,burns faster than the piston can accelerate down but atdc. Newer Ducati use compression ratios of 11:1 or higher and as I stated if your compression ratio is over 10.5 :1 you need a higher octane. Higher octane fuels by definition burn slower,at a slower flame propagation than low octane fuels.modifications to cylinder heads are designed to raise compression by increasing the break mean effective pressure of the charge entering the cylinder effectively doing the same thing as decreasing the volume of the combustion chamber( raising the compression ratio) bigger charge more pressure,more heat more power.
by the way if you put someone who is 200 lbs on the same engine as someone who is 100 lbs,you increase the compression . If you ride into the wind you increase the compression , if you tow you increase the compression .If you ride uphill you increase the compression .But the ratio stays the same.
It is all about pressure,temperature and volume.
Two plugs,two flame fronts propagating burning the complete charge faster not faster flame propagation
Also 87 octane fuel has no more or less energy than 89 or 91 octane fuels.energy output is the same regardless of octane rating
The noise you hear in either case of pinging or detonation is your piston forcing the rod into the crankshaft and in the worst case all of the above shattering from pressure that exceeds their design.
rant off................

higgy wrote:pure bullshit,You are confused. Boyles law rules. pvt1 = pvt2 period. Increasing the temperature or the pressure on the fuel makes it burn faster( at a higher flame propagation)Detonation or its cousin pinging is as you state due to instant combustion brought on by either higher pressure or higher temperature than the octane of the fuel is rated for.Detonation is way to fast burning,charge ignites while the piston is still moving up btdc,all at once,pinging is too fast burning,burns faster than the piston can accelerate down but atdc. Newer Ducati use compression ratios of 11:1 or higher and as I stated if your compression ratio is over 10.5 :1 you need a higher octane. Higher octane fuels by definition burn slower,at a slower flame propagation than low octane fuels.modifications to cylinder heads are designed to raise compression by increasing the break mean effective pressure of the charge entering the cylinder effectively doing the same thing as decreasing the volume of the combustion chamber( raising the compression ratio) bigger charge more pressure,more heat more power.
by the way if you put someone who is 200 lbs on the same engine as someone who is 100 lbs,you increase the compression . If you ride into the wind you increase the compression , if you tow you increase the compression .If you ride uphill you increase the compression .But the ratio stays the same.
It is all about pressure,temperature and volume.
Two plugs,two flame fronts propagating burning the complete charge faster not faster flame propagation
Also 87 octane fuel has no more or less energy than 89 or 91 octane fuels.energy output is the same regardless of octane rating
The noise you hear in either case of pinging or detonation is your piston forcing the rod into the crankshaft and in the worst case all of the above shattering from pressure that exceeds their design.
rant off................

Well NOW I'm confused, that's certain. Help me out - which term of Boyle's Law represents the fuel mixture burning?

There is NOTHING in Boyles law that has anything to do with a fuel burning. It doesn't take combustion into account. I'm confused why you brought a formula that doesn't apply to combustion into a post about flame speed?

Higher octane fuels BY DEFINITION burn slower? I'm confused by that. Post a defintion of octane rating from any tech site that puts burn rate in the definition so I can see what I've been missing all these years.

I'm confused why you talk about static and dynamic compression. So what? I never mentioned that. I never said anything about power output or octane requirements, I simply said higher octane gasoline does not control knock by burning slower. And it doesn't. (Oops, I just reread my post and what I really said was it doesn't burn slower.)

And THIS has me really confused:

Two plugs,two flame fronts propagating burning the complete charge faster not faster flame propagation

My confusion lies in that it seems like you are implying it's ok to have the mixture burn in X amount of time because of turblulence, but not ok to have it burn in X amount of time because of the flame speed itself. The mixture is getting burned in the same amount of time... assuming you aren't requiring the flame speed to go supersonic I'm missing how the pressure/temp profiles will be different between the two cases. This amount of fuel in this amount of time either way. And it's all about pressure and temp, you said so yourself. Oh wait, you added volume. I'm confused on how a different volume at the same temp and pressure will matter. Put the mix in a 45cc chamber at a given temp and pressure or a 50cc chamber at the given temp and pressure, the mix will still have the same delay before it auto-ignites. The chemistry relies on the temp and pressure, not the volume.

And yes, the damage caused by detonation is due to shock waves, not by "pressure that exceeds their design". The shock wave does cause pressure spikes for sure, it's the spikes that do the damage. The spike destroys the boundry layer which protects the piston from the heat of combustion, overheating the part. And then the pressure spikes hammer the surface of the piston/head. The pressure doesn't simply squeeze it until something shatters.

FWIW If what I've posted is bullshit, you might want to get in touch with the people at Crane Cams and Shell Oil company, plus the publishers of every text on engine theory I've ever seen.

From Shell Oil:
http://www.shell.com/home/Framework?sit ... _2101.html

Q: How is the octane rating determined?
A: The octane rating specifies the knock resistance of the carburettor fiel. Isooctane, which is defined as having an octane rating of 100 and n-heptane, which has a defined octane rating of 0, are used as a comparison mix to determine the octane rating. Octane ratings are determined in CFR test engines, which are standard world-wide. [Hmm, no mention of flame speed in Shell's definition...]


Crane Cams knows a little about this stuff I would hope:
http://www.cranecams.com/?show=newsLetters&no=119

Playing ?The Octane Game?, Or. . . Is ?Race Gas? The Same Stuff As ?Av-Gas??

Many racers mistakenly believe that octane is the most important factor in selecting a fuel for racing. They think that the higher the octane number, the more power a fuel will provide. This is misguided thinking which totally ignores the most critical feature of a racing fuel - flame speed at a given cylinder pressure. Octane number only measures a fuel?s resistance to detonation and pre-ignition. It does not have any direct relationship to flame speed, which is critical to maximizing cylinder pressure (horsepower).

Racing fuels are designed to maximize flame speeds at high cylinder pressures typical of competition and/or supercharged engines. They are also designed for high engine speeds (above 5,000 RPM). By contrast, aviation gasoline is designed for relatively low compression engines operating in the 2,700 ? 2,800 RPM range at 8,000 to 10,000 ft. altitude. Quite different from a racing engine! Compared to racing fuel, the transient response (measure of an engine?s ?throttle response;? the ability to rev quickly) of aviation fuel is poor. This is a result of the blend of the gasoline and is no way measured by octane rating. Unfortunately, there is no quick and easy way to measure the various types of racing fuel, and don?t assume that the highest octane is the quickest fuel.


The people at Shell Oil company seem to disagree with the the defined relationship between octane rating and flame speed. Ease my confusion. Explain where they're wrong.



And not that an astonomy site is an obvious source but it shows up and was interesting.
http://www.absoluteastronomy.com/topics/Octane_rating

Unfortunately the site doesn't copy/paste well so you'll have to check it out for yourself.

Not sure who Thor racing is but this is what their site says
http://www.thor-racing.co.uk/Octane_Rating-149.asp

What fuel property does the Octane Rating measure?
The fuel property the octane ratings measure is the ability of the unburnt end gases to spontaneously ignite under the specified test conditions. Within the chemical structure of the fuel is the ability to withstand pre-flame conditions without decomposing into species that will autoignite before the flame-front arrives. Different reaction mechanisms, occurring at various stages of the pre-flame compression stroke, are responsible for the undesirable, easily-autoignitable, end gases.

During the oxidation of a hydrocarbon fuel, the hydrogen atoms are removed one at a time from the molecule by reactions with small radical species (such as OH and HO2), and O and H atoms. The strength of carbon-hydrogen bonds depends on what the carbon is connected to. Straight chain HCs such as normal heptane have secondary C-H bonds that are significantly weaker than the primary C-H bonds present in branched chain HCs like iso-octane.

The octane rating of hydrocarbons is determined by the structure of the molecule, with long, straight hydrocarbon chains producing large amounts of easily-autoignitable pre-flame decomposition species, while branched and aromatic hydrocarbons are more resistant. This also explains why the octane ratings of paraffins consistently decrease with carbon number. In real life, the unburnt "end gases" ahead of the flame front encounter temperatures up to about 700C due to compression and radiant and conductive heating, and commence a series of pre-flame reactions. These reactions occur at different thermal stages, with the initial stage (below 400C) commencing with the addition of molecular oxygen to alkyl radicals, followed by the internal transfer of hydrogen atoms within the new radical to form an unsaturated, oxygen-containing species. These new species are susceptible to chain branching involving the HO2 radical during the intermediate temperature stage (400-600C), mainly through the production of OH radicals. Above 600C, the most important reaction that produces chain branching is the reaction of one hydrogen atom radical with molecular oxygen to form O and OH radicals.

The addition of additives such as alkyl lead and oxygenates can significantly affect the pre-flame reaction pathways. Antiknock additives work by interfering at different points in the pre-flame reactions, with the oxygenates retarding undesirable low temperature reactions, and the alkyl lead compounds react in the intermediate temperature region to deactivate the major undesirable chain branching sequence.

The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:-

1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.

2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane.

My "pure bullshit" is supported by any number of sources. And yes, I know you can find sources on the 'net to support any claim. I tried to stick with more reputable ones here but I don't really have time to wade through everything at work - these were handy from a simple Google search. I suppose I could dig out my old texts. They're all about 25 years old now but I doubt the physics has changed much. That said, I'd be happy to see more current sources you have if you care to post them.