TW200 Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
830 Posts
Discussion Starter #1
I know that low compression engines are better with low octane fuel - faster burning fuel is better than slower burning fuel unless you are dealing with high compression motors -- it;s better to have as low an octane fuel that will burn well in your particular motor - better combustion and less carbon build up. But....I was curious if at very high altitude since air is thinner is it better to have slower burning fuel? The answer is no - higher altitude actually has the effect of lowering your compression more than at sea level - anyhoo here is the source I found for anyone else that is interested. I'm going to try and buy 85 octane in NV on the way to Sweet Water.

https://mechanics.stackexchange.com/questions/6920/can-i-use-lower-octane-fuel-at-high-elevation
 

·
Registered
Joined
·
1,077 Posts
Careful with the ethanol % on 85 octane.
I have run 87 octane regularly up to 8,000 feet elevation, with satisfaction.
 

·
Registered
Joined
·
830 Posts
Discussion Starter #4
good point...have not factored in the alcohol.... I think there's a spot on 395 by a Walmart that has non ethanol for a little more $ - I'll check it out.

Thanks
 

·
Registered
Joined
·
1,865 Posts
Thanks for answering this I was going to ask the same question.
 

·
Registered
Joined
·
1,927 Posts
List of non-ethanol gas stations & other stuff in the U.S.
There are others, but I think this one is the best.

https://www.pure-gas.org/index.jsp

Don't forget...Google is your friend!
 

·
Registered
Joined
·
464 Posts
Unless you get your TW airborne you are not at a high altitude but at a high ground elevation.

The higher the elevation you travel will result in lower engine compression and you will have less need for a higher octane fuel.
 

·
Registered
Joined
·
19,391 Posts
Spoken like a true pilot!
Now a month ago I rode maybe 9,960 ft max elevation burning 91 octane atop a 10.25 Wiseco piston and had no noticable ill effects. Maybe it was the full moon.
However today’s comments are by those returning with me for for the next full moon and an intended brief excision over 11,300 summit and possibly 3 days of extended 9,000ft plus riding. Thus our questions have a practical application.
Perhaps I should dump all my bike and spare 91-test fuel into the 4-wheel mother ship and instead load up on 87 octane while also directing Adam-in-Nevada to fill my 5-gallon can with the cheap stuff...after all, nothings too cheap for my dear TW friends.
 

·
Registered
Joined
·
1,077 Posts
I visit higher elevations frequently.
The only changes I have made for rides/drives above 5,000 feet is to further advance timing, when that is an option.
On the 350 ci V-8 in my Datsun, I left the distributor clamp loose enough to twist the cap.
Not that a PL620 pickup needed more than 300+ HP, but it was more fuel efficient.
Wheeler Peak, Great Basin, June 2014.JPG
V8 under the hood.jpg
 

·
Registered
Joined
·
830 Posts
Discussion Starter #10
Unless you get your TW airborne you are not at a high altitude but at a high ground elevation.

The higher the elevation you travel will result in lower engine compression and you will have less need for a higher octane fuel.
My attitude gets better at higher altitudes....I mean elevations! Thanks for the reminder - but, if both my tires are off the ground (seldom happens) at 10,000 feet elevation ----- while I am defying gravity...I am at 10,000+ feet Altitude, I say this with the best of attitudes.

Sorry I have a coffee buzz Donzo
 

·
Registered
Joined
·
1,001 Posts
If you went off an open drop of 10,000 feet; from the ground now below you, both your elevation and altitude would be 10,000 feet --- for a very short period of time!

The elevation vs altitude "argument" has too many variables that can make each view correct. Each measurement could be required to be based on a fixed point of reference, such as sea level. Aeronautics might use air pressure (simplified) to determine altitude in instances. But if an airliner was required to maintain 30,000 feet altitude "using the 'above the ground below'" argument; the pilots might have fun, but the passengers might be complaining of the up and down roller coaster ride over groups of mountains. Climb 10,000 feet, dive 10,000 feet, climb 10,000 feet; and so on.

Funny though; I've never heard it called "elevation sickness", even though everyone's feet or wheels are firmly planted on the ground (in most cases).
 
1 - 13 of 13 Posts
Top