Octane--Is 87 REALLY Right?

[mcatrophy]

... Higher octane burns cooler which is why it's needed to prevent pinging.But if the octane is too high, it will foul your plugs. Too low, and it will burn them.

...

Higher octane fuel needs a higher temperature to self-ignite, the burn temperature is essentially the same. "Pinking" ("pinging" or "knocking") occurs when the increase in temperature during the compression stroke ignites the fuel (which, of course, is how diesel engines work) instead of waiting for the spark plug to fire.

Mechanically nasty (trying to push the piston down on the up-stroke), and the burn usually starts on some deposit such as carbon (with retains heat from the previous combustion), so concentrating heat on (for instance) the top of the piston or the valve seats, which can locally melt the metal. It can also rock the piston in the bore.

Engines that have knock sensors can reduce the amount of mixture input, which reduces the compression pressure, reduces the temperature of the compression, so stopping the pre-ignition.

The FJR does not have a knock sensor.

Any difference felt in power is either because there are different additives (ethanol or whatever) or maybe in the mind of the rider ("It cost more, I must be feeling the benefit"). There is no significant difference in energy per unit volume in different octane pump fuel of similar composition.

 

[Bounce]

Any difference felt in power is... in the mind of the rider ("It cost more, I must be feeling the benefit").

This^

Without dyno numbers to back it up, it's snake oil when used in an engine designed to run on lower octane.

 

[MrZappo]

Any difference felt in power is... in the mind of the rider ("It cost more, I must be feeling the benefit").

This^

Without dyno numbers to back it up, it's snake oil when used in an engine designed to run on lower octane.

This report was done for cars but probably very much the same thing ... In any event, I didn't totally agree with the tests and thought they could have been done a little better. But, it seemed reasonable and was probably the closest thing to an actual test I have seen ....

They didn't address cars that NEED premium like turbo charged cars etc .. Also, they didn't talk about cars without computers/knock sensors. And motorcycles like the FJR do not have knock sensors etc but, it is not relevant as they were designed for 87 (Regular) anyways ...

There is a lot of extraneous mumbo jumbo but overall it was interesting ...

 

[rushes]

Pointless discussion.

My old timey british bikes will not run on high octane fuel. (Well, they'll run but not well. Will not idle for sure.)

They like as low octane non ethanol as I can find.

Compression, timing, mixture...

We should embrace playing with fossil fuels while we can.

Our kids and grandkids will be playing with batteries and such. How boring...

 

[SacramentoMike]

Thanks for the replies. I got what I asked for. The discussion--and the hard time.

 

[beemerdons]

Thanks for the replies. I got what I asked for. The discussion--and the hard time.

Yo SacramentoMiguel, if you want the REALLY HARD TIME contact Old Michael! JSNS, aye!

 

[SacramentoMike]

That guy should be DOING hard time.

 

[dcarver]

That guy should be DOING hard time.

... and my name is Hard Time!

fixed it for you Mike!

 

[pista]

Use what the owners manual recommends.

For the FJR, it's 87 octane at sea level. (At higher altitudes a lower octane is acceptable.)

The octane required for any engine is a function of cylinder pressure when the air/gas mixture is ignited. A higher compression engine typically requires a higher octane level gasoline to prevent detonation.

Here's why:

The air/fuel mixture should be ignited by the sparkplug and not as a result of preignition. Preignition is that "knocking" sound heard when the air/gasoline mixture ignites too fast. Instead of a nice even flame, it "explodes" or detonates.

High octane gasoline prevents this by burning slower.

We tend to think of the spark as being instantaneaus. An explosion inside the cylinder head driving the piston down.

In reality the flame has to burn at an acceptable rate called "flame propagation" that's initiated by the sparkplug and spreads throughout the cylinder driving the piston downwards. If the fuel burns too fast, you have pre-ignition. That is the only reason you would need an higher octane fuel!

BTW, an easy way to prevent preignition is to ****** the ignition timing to occur closer to TDC. This is not ideal because the net result is a loss of horsepower. Modern engines equipped with "knock sensers" automatically do this to prevent the engine from damage. So if the manufacturer designs the engine components ie: ignition timing, cam timing, compression ratio, etc in such a way that high octane gasoline is required, then by all means use it to get the performance the engine was designed to deliver.

Otherwise save your money and put regular in there. Your FJR doesn't mind.

 

[hppants]

An increase in Octane (which corresponds to a decrease in the fuel's burn rate) has nothing to do with temperature.

Semi-related, on our recent trip west, Redfish Hunter and I were very impressed with our increase in mileage as we climbed in elevation. About 6000 feet, I bought 85 octane and heard nor sensed any pre-ignition ping. Of course the power of the motorcycle was down within increases in elevation. But the ECU did a fantastic job of leaning the mixture to compensate for the reduction in O2. All other things considered relatively equal, a tank of about 43 MPG here on the Gulf Coast would equate to 51 or even a little more in the upper elevations.

I can attest to this increase on the Gen III only, as I never took my Gen I bike that high in altitude.

 

[RossKean]

Very similar observation with fuel consumption at elevation on Gen II.

 

[HyperPete]

Use what the owners manual recommends. For the FJR, it's 87 octane at sea level. (At higher altitudes a lower octane is acceptable.)

The octane required for any engine is a function of cylinder pressure when the air/gas mixture is ignited. A higher compression engine typically requires a higher octane level gasoline to prevent detonation.

Here's why:

The air/fuel mixture should be ignited by the sparkplug and not as a result of preignition. Preignition is that "knocking" sound heard when the air/gasoline mixture ignites too fast. Instead of a nice even flame, it "explodes" or detonates.

High octane gasoline prevents this by burning slower.

We tend to think of the spark as being instantaneous. An explosion inside the cylinder head driving the piston down.

In reality the flame has to burn at an acceptable rate called "flame propagation" that's initiated by the sparkplug and spreads throughout the cylinder driving the piston downwards. If the fuel burns too fast, you have pre-ignition. That is the only reason you would need an higher octane fuel!

BTW, an easy way to prevent preignition is to ****** the ignition timing to occur closer to TDC. This is not ideal because the net result is a loss of horsepower. Modern engines equipped with "knock sensors" automatically do this to prevent the engine from damage. So if the manufacturer designs the engine components ie: ignition timing, cam timing, compression ratio, etc in such a way that high octane gasoline is required, then by all means use it to get the performance the engine was designed to deliver.

Otherwise save your money and put regular in there. Your FJR doesn't mind.

I was about to post information on burn speed, but you covered it nicely.

One can see the effect of very high octane in race cars at night, when the flames are coming out of the exhaust. I would be more worried about burning exhaust valves from running excessively high octane (race fuel or AV gas) than anything. I doubt one has to worry too much about any grade of normal "pump gas."

I, for one, choose not to throw my money away on higher octane fuel than is needed. Besides, since it's a slower burn, and may be burning in the exhaust, I would expect that higher than required octane will increase heat in the exhaust, and lower fuel economy (slightly.)

My M109R requires 91 octane, and it pings if I am forced to fill with lower octane gas. I'm glad to hear that the FJRs only need 87!

 

[tjwallib]

It is my understanding that higher octane fuel doesn't have a slower flame front propagation,,,,,,,higher octane rated fuels will have a lesser tendency for "pre ignition", either from compression in the cylinder or a "hot spot" in the cylinder or valve area.

Pinging or knocking can be caused by timing too far advanced where the expansion of gases are working against the rising piston, or a "pre ignition" from another source other than the spark plug and the two flame fronts meeting each other in the cylinder instead of an even flame front spread and heat expansion in the cylinder.

The reason you see flames from headers of race or drag cars, is the AFR is so rich that there is no way possible for all of the fuel to be consumed during the power stroke in the cylinders. The flame front or burning/expansion of the fuel continues during the exhaust stroke and out the headers,,,,,,,,,Not just because of a higher octane fuel.

Some of the drag cars are being run with fuel mixtures where they are almost "hydro locked".

 

[Spud]

I'll bet 95% of all the gas I've run through my bike has been 85 Octane. I live at 5000 feet and all the good roads go up from here. Just grab the handle on the far left of the pump (as long as it's black, not green) and you'll be just fine.

 

[mcatrophy]

... Just grab the handle ... (as long as it's black, not green) and you'll be just fine.

If ever you come to the UK or some other European countries, be aware the black ones are diesel, the green are petrol (gas). Check the green ones' numbers for the octane value.
Random picture of a Spanish pump:

(Click on image for larger view)

 

[El Toro]

The European pumps are typically displaying what's called the Research Octane Number. The Motor Octane Number is generally lower for blended fuels. In the US what's displayed is the Anti Knock Index, which is the average of the Research Octane Number and the Motor Octane Number. The difference between the RON and MON is the fuel's sensitivity.

Both RON and MON are determined on the same test rig (variable compression ratio engine specially designed for this test), but under different test conditions. When the tests were first posed, the MON better reflected conditions that would be experienced on the road.

Before the introduction of tetraethyl lead, octane numbers were quite low, and engines were limited to lower compression ratios than are common today. Thermal efficiency is tied to compression ratio (higher compression ratio gives higher thermal efficiency), so higher octane fuels made it possible to run with higher compression ratios, and higher compression ratios made it possible to improve energy conversion efficiency. Unfortunately, higher compression also leads to greater normal forces for the sealing ring's mating against the cylinder wall, so this increases friction and reduces efficiency. As a consequence, there's not much payoff for going to higher compression ratios than say 13 or 14 in Otto Cycle (spark ignition) engines.

As an aside, since the alcohols have high octane ratings, there is quite a bit of fuel research presently being conducted to look at how overall efficiency might be affected if engines were designed specifically to run on blends like E30 and higher.

And FWIW, the octane rating compares the ability of the subject fuel blend to resist compression ignition to the ability of 2,2,4 Trimethylpentane to resist compression ignition.

2,2,4 Trimethylpentane is an Alkane with 8 carbons and 18 hydrogens, organized with a pentane backbone and with two methyl groups hanging on the second carbon, and one methyl group hanging on the fourth carbon. The formal name for this hydrocarbon is Octane (Oct for the 8 carbons, and ane denoting that the hydrocarbon is in the Alkane family). In the fuel industry 2,2,4 Trimethylpentane is known as Iso-Octane, Iso indicating that it is an isomer of Octane. Iso-Octane has an Octane rating of 100, for 100% as good as itself ...

And, as another interesting tidbit, another way to organize 8 carbons and 18 hydrogens is in the N-Octane form, the N standing for Normal. Normal Octane has a LOUSY Octane rating.

Yet both have essentially the same enthalpy of formation. And when they combust, they both release very similar amounts of heat as a consequence. The calorific value of a fuel is really dependent on the number of bonds that are broken, and both Iso-Octane and N-Octane have the same number of bonds between carbon and hydrogen atoms.

 

[El Toro]

And for the OP, my experience is that the FJR runs just fine on 87 octane, 89 octane, 91 octane, and 93 octane, and that the differences one sees in the gas mileage may well be related to the components of the blend, rather than on the octane rating.

Gasoline and Gasohol are blends of maybe five or so different hydrocarbons, in different amounts, blended in order to give the target

octane rating

cold start performance

energy content

cost

and maybe a few other descriptors.

 

[G Squared]

Admin,,, for the love of all things holy, do the humane thing and Kevorkian this thread!!!!!

 

[Ignacio]

Admin,,, for the love of all things holy, do the humane thing and Kevorkian this thread!!!!!

Why? If I do that then the people hell-bent on regurgitating NEPRT details will just start another thread and do it all over again for the twenty-umpteenth-deja-vu time. It's fine where it is.

 

[MrZappo]

Ok, so I am clear, the fjr requires premium and will implode on anything less. Is that right?

Definitely need some clarity and consensus on the matter.

Just because the engineers that conceived of, designed, and refined an engine that will go 300,000 miles or more, is that any reason to believe them?

Their clear recommendations in the owners manual are highly suspect.

What subterfuge must this documentation be based on?

It's just reckless in my opinion.

87 octane indeed.