octane

[Jerry]

Do a search on octane and you will find som interesting web sites. To summarize:

Octane is a measure of a fuel's ability to ignite. Low octange fuel can be ignited by carbon or hot spots in the combustion chamber. High octane requires a hotter flash point, such as supplied by a spark plug.

Higher octange fuel is not 'more powerful' than low octane fuel.
Pump gas is an average of the two different ways of rating octane
A number of things can affect your performance, including ambient temperature. Your bike will run better in cooler weather.

Compression ratio on the XS was 9.2 to 1 in the original '78. later versions run lower compression ratios, such as 9.0 to 1 in the XJ.

Gas contains other additives, such as Techron. Some gas is blended for geographical areas or summer/winter changes. I suspect that if you see a change in performance (smoother running, more power, yada yada yada that it is not so much as a difference in octane as it is in the blend or other additives.

For a technical discussion of octane and how it is measured, see at least :
http://www.prime-mover.org/engines/G...es/octane.html

Another good page, with more on pump gas ratings, is
http://www.grapeaperacing.com/GrapeA...fueloctane.cfm

These will tell you more than you wanted to know about octane.

[Bill]

87 octane in airplanes

Dark Horse wrote:

Aircraft engines which are high compression (11.5:1.0 to 12.5:1.0) use fuels with octane levels around 94 - 96.

Heck, I use 87 octane in my motorcycles AND my airplane!

[MartyA]

Regarding ethanol; I worked for a company that supplied Delphi with 10 million fuel pump motor sub-assemblies per year. The components were plated with zinc dichromate and the plan was to withstand an average of (if I recall) 90,000 miles. When they started to change to the ethanol, which if I remember is from corn, the life test results were cut in half. The same components were failing - rusting - much much sooner. They ended up plating with tin and something else, and I left the company before the issue was resolved.

I wonder what that stuff is doing to your innards?

Regarding the low mpg, you must have something wrong, that is a lot of gas going through there. On my 78E, I get 36-38 at sustained 70+mph, 40 mpg (last trip 42) on the 55 mph byways around here. I have 4 K&N's, some black 4-1 aging exhaust, and I think the PO put in 2 size larger jets, although I am not sure now after reading all the jet discussions.

Maybe someone is stealing your gas at night?

[sixtysix]

Check out this tip for improving your milage.


http://www.xs11.com/forum/showthread...=&threadid=746

[kenkrieger]

Try anyting other than full throttle operation and it will result in more miles per galloon,,,,,hehe,,,,it worked for me,,,,,,lol,,,,,,YMMV

[Dark Horse]

Bill,

My boss has a Cessna 182 that is certified for lower octane fuels also. How does that work?

[mn2346]

The motor of that Cessna must be low compression (or about normal for us). There's nothing magical in aeroplanes that would require higher octane fuel just because they are planes.

It's just that plane engines are run at a 70% (?) loads all the time and usually they are designed to give max performance with the lightest configuration possible. Easy way to make lot's of power is to boost the compression to maximum. Planes don't use low revolutions and low rpm torque is not that important.

-Marko

[Bill]

Mogas and aircraft engines...

Bob Udy wrote:

My boss has a Cessna 182 that is certified for lower octane fuels also. How does that work?

When I got my '56 Tri Pacer approved for car gas there were two companies that could issue the certificate which is based on both the engine and airframe. I think I paid $1.00 per HP, or $150 for my old Piper. In my case, and perhaps your boss' 182, they were originally designed for 80/87 Avgas, so regular Mogas is closer to the original spec than the 100 low lead that's sold at most airports. OTOH, local stock car guys like to use the 100LL in their race cars!

Marko wrote:

Planes don't use low revolutions and low rpm torque is not that important.

Actually, piston engine aircraft run very slow compared to motorcycles or high performance cars. At high RPM the prop tips could go supersonic and cause all kinds of problems. My plane runs at about 2600 RPM flat out at sea level.

Gary LaPook, or any other recip drivers, please correct me if I got any of the details wrong.

[mn2346]

rpm

Interesting, I was under the impression that plane rpm's would be somewhere in the high 5k range. Is 2.6k on the upper edge or in the middle of rpm range?

I remember that some of the people on the list were using the 100LL in Xs (there was a thread about this last year). Main motivation was increased octane rate and it seamed to clean the engine and carburators?

-Marko

[Bill]

Re: rpm

Marko wrote:

I was under the impression that plane rpm's would be somewhere in the high 5k range. Is 2.6k on the upper edge or in the middle of rpm range?

My experience is limited to my Tri Pacer, a few Cessnas, a Cherokee and a Lake Ampibian. All of them run in the 2400 to 2600 RPM range. Some experimental racers push up the RPM, but I don't know how far.

I remember that some of the people on the list were using the 100LL in Xs (there was a thread about this last year). Main motivation was increased octane rate and it seamed to clean the engine and carburators?

I don't know about that, but Avgas is supposed to be more stable for longer storage. However, an occasional treatment with a product such as Techron or Sea Foam will keep your fuel system nice and clean.

[Jdwags]

All i know is i get better mileage with higher octane in both my car and my scoot...

and it seems more peppy.....

since the last thread on this though i went to mid grade and it still seems good... if the pickup wires were workign right

[32bat]

Octane

I have on occaision filled up with premium gas, since I wasn't buying 30 gallons at a time, I honestly can say I didn't ever notice any difference. But I do still do it from time to time.

[JP]

Originally posted by Jdwags
All i know is i get better mileage with higher octane in both my car and my scoot...

Makes ya wonder what kind of crap they're diluting the cheap stuff with to keep their costs down, don't it?

Is that at a "major brand" station or "Ferd's Friendly Fillin' Station & Falafel Hut?"

[crunchbird]

That's right, JP! I use the 89, not because it runs better than good 87, but because I think when they dump their bad hooch they put it in the 87.

[Robert Haller]

Originally posted by Dragonrider
I get demonstratably better milage on the 87 octane ...

Wow, I just refilled my tank and I got the best gas milage I ever have - 50 mpg. Usually I'm doing good to get 40 mpg with regular gas. It's 87 octane for me from now on.