Fuel requirement

I have a pretty basic question. The previous owner of my bike couldn't find the owners manual, and I can't find this information anywhere. The spec sheet on VFRworld lists the compression of the V-Tech engine as 11.6 to 1. In my experience, carburated big block V-8s, this kind of compression requires the highest grade fuel you can find, if not additives. I put the cheap stuff in out of habit the first couple times I filled it, but noticed no difference with the higher grades. Any one have any opinions or know what grade is required? I have no real interest in damaging the engine.
Thanks,
Dean

 

Your bike is designed to run on the low grade fuel. Even though the compression ratio is reasonably high the way they design engines these days compensates for that, it's all about fuel mixing, airflow etc. You will hear a lot say you should run higher grades of gas. This is not necessary. I don't think it will do any harm but it's not necessary. You will not get more power from the higher grade of gas. Some believe that the higher grades of gas will run cleaner and develop fewer deposits over time. I am not convinced myself but then I am not a fuel chemist. Given that it usually takes very high milages for deposits to become an issue I doubt that is ever a problem for anyone but the super high mileage touring crowd. So go with the low and save some money.

 

FWIW, I get noticeably better tank range using higher grade fuel.

 

And yet, I find no difference with my bike. I've tried all three grades ... no dif. In fuel mileage anyway ... my bike fells a bit stronger with reg as opposed to high-test (purely subjective observation :smile: ) too many variables involved I guess; alt, temp, driving habits, et al. Did I read somewhere that reg fuel burns hotter than hi-test? Anyways, FWIW, my manual calls for 86 oct .... around here (PNW) that equates to 87 oct reg.

 

gasoline octane is a measurment of its' ability to resist detonation, or early detonation, it has nothing to do with mileage and/or energy capacity

 

Thanks guys, that helps.
Spike is right, the octane rating is just basically a measure of the auto ignition temperature. I wasn't expceting better milage or performance with high test, I'm just suprised I didn't have more engine noise with 87.

 

The lower the octane rating the easier it burns. That's why low compression engines run worse (usually) when run with higher octane fuel. Some makes are designed to run lower octane with higher compression. If you don't hear any pinging then run the lowest you can get away with.

Doug

 

Surely more than you wanted to know.....courtesy of Marshall Brain and http://www.howstuffworks.com
(ps - i bought my first motorcycle, a 1982 Nighthawk 450 from Mr. Brain in 1989)

>>>>>>>
If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During WWI, it was discovered that you can add a chemical called tetraethyl lead (TEL) to gasoline and significantly improve its octane rating above the octane/heptane combination. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

Lead clogs a catalytic converter and renders it inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).
When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline (known as AvGas), and octane ratings of 100 or more are commonly used in super-high-performance piston airplane engines. In the case of AvGas, 100 is the gasoline's performance rating, not the percentage of actual octane in the gas. The addition of TEL boosts the compression level of the gasoline -- it doesn't add more octane.
>>>>>>>

***HowStuffWorks is the leading source of credible, unbiased, and easy-to-understand explanations of how the world actually works. Founded by North Carolina State University Professor Marshall Brain in 1998, the site has since grown to be an award-winning online resource for millions of people of all ages.

 

I'm still confused (sorry, very non-mechanical minded!)

I have a 1990 VFR. Can I assume that I don't need to run high octane fuel? I alternate between standard (low octane) and high octane. I dont hear any difference, or feel any difference in performace?

Did they have different octane fuel options at the bowser back then?

Thanks

 

I always go with the lowest octane rating recommended by the manufacture. My 99vfr is 86. So at the gas station, I use 87 because it is the lowest I can go. I believe it would be a problem I would hear it as it would ping. I use this principle on all of my engines and have never had a problem.

 

91 minimum

My manual says "use unleaded petrol with an octane rating of 91 or higher"

"If you use petrol containing alcohol be sure its octane is at least as high as that recommended" "do not use petrol containing more than 5% methanol"


Where possible, I use the highest octane unleaded I can find. (98 or 95) I reckon I get better fuel economy than the cheaper fuel.
Higher octane fuels have more energy but burn longer, = less of an explosion more of a controlled combustion, which is softer and easier on your engine.

My understanding is, using lower than 91, (on a 2006 model) you risk pre ignition "detonation" or "pinking" which can cause damage.

But wait, the lowest octane availabe in Aussie is 91. So you should be OK whatever you choose.

Check out this link.
http://member.rivernet.com.au/btaylor/BMWText/technical/FuelOctane.html

 

Octane has nothing to do with how much energy the fuel has.

Look at the Ethanol fuel they sell, the Octane rating on that is over 100 I know for certain, I want to say like 109 or 110 maybe? Yet, if you have a flex fuel vehicle, and you use ethanol instead of gas, your fuel mileage will drop about 30% according to published reports. Because it contains less energy, or BTU's per gallon that regular old gas.

I run the lowest octane availible, in all my vehicles, never had an issue. My '98 VFR had 48,000 miles on it when it was stolen and ran like a top.

Note the the way octane is measured is not the same everywhere, so some of this discussion will be affected by that.

Nearly every published report tells you to use the lowest octane fuel recommended in your manual, where you don't get pinging.

gotta go....

 

I stand corrected, on one point. There is no ADVANTAGE in using an octane number greater than recommended.

However - if you use an octane LOWER than reccomended, you could cause ENGINE DAMAGE.

With all the fuels about now days- in the outback, you dont know exactly whats in thier pump. To play it safe I will choose the next octane above recomended minimum. (95) and i only use petroleum - not blended.


http://www.repairfaq.org/filipg/AUTO/F_Gasoline6.html

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.
If you are already using the proper octane fuel, you will not obtain more power from higher octane fuels. The engine will be already operating at optimum settings, and a higher octane should have no effect on the management system. Your driveability and fuel economy will remain the same. The higher octane fuel costs more, so you are just throwing money away. If you are already using a fuel with an octane rating slightly below the optimum, then using a higher octane fuel will cause the engine management system to move to the optimum settings, possibly resulting in both increased power and improved fuel economy. You may be able to change octanes between seasons ( reduce octane in winter ) to obtain the most cost-effective fuel without loss of driveability. Once you have identified the fuel that keeps the engine at optimum settings, there is no advantage in moving to an even higher octane fuel. The manufacturer's recommendation is conservative, so you may be able to carefully reduce the fuel octane. The penalty for getting it badly wrong, and not realising that you have, could be expensive engine damage.