Why do we need 91 or higher octane?
Seasoned HDF Member
Joined: Oct 2019
Posts: 10,804
Likes: 7,444
From: OH
I agree use what the owners manual says or higher. I sometimes will run 91 or 93, but my older carbed bikes run on regular 87 as per the owners manual. I havnet really noticed any discernable difference running 93. The bike doesnt go faster or anything like that.
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,586
Likes: 6,435
From: Honah Lee
The original question is something that I've wondered about as well. I do run the higher octane in my bike as recommended. What gets me thinking is how bad is it to run a lower octane?
When I did my trip to Alaska a few years ago, most of the gas I could buy at some point was 87 octane. There wasn't even an 89 octane option. I had a KLR650, so I never worried about it, but, I often think of doing another Alaska trip on my Harley. I know people do similar trips on Harleys, so is it all that bad to run 87 octane through a few tanks of gas? Will I lessen the length of life of the engine?
I'm guessing there isn't a hard and fast answer.
When I did my trip to Alaska a few years ago, most of the gas I could buy at some point was 87 octane. There wasn't even an 89 octane option. I had a KLR650, so I never worried about it, but, I often think of doing another Alaska trip on my Harley. I know people do similar trips on Harleys, so is it all that bad to run 87 octane through a few tanks of gas? Will I lessen the length of life of the engine?
I'm guessing there isn't a hard and fast answer.
On those 150 nights, I was literally hugging engine. Nothing sounds like a Harley at 30 degrees weather. Don't think you could make it ping.
Too old for that silliness now.
What is the average temperature you would be running at in Alaska?
Seasoned HDF Member
Joined: May 2012
Posts: 32,934
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From: Carlsbad, CA
I had a real world example of the impact of lower octane fuel on my TriGlide. I bought the ‘12 TriGlide in Oregon, and had the dealer a Stage with the SE 255 cams, They tuned it with 92 octane. Years later, we were in Death Valley, and with my tank hovering nest empty I filled with what was available 87 octane. The road out of Death Valley was a steep 3,000’ climb. I could hear the “tinging” sound you get when the motor is starting to knock, and the knock suppression kicks in. With the power reduction, due to the knock suppression, it was a very slow climb. I’ve climbed just as steep climbs before and after this...with at least 91 octane and never had that issue.
so, yeah if you ride on the flats, and don’t twist the throttle much, you may not notice a difference with lower octane. But put a heavy load on the motor, with lower octane, and the knock suppression will kick in and reduce your power output.
so, yeah if you ride on the flats, and don’t twist the throttle much, you may not notice a difference with lower octane. But put a heavy load on the motor, with lower octane, and the knock suppression will kick in and reduce your power output.
Also, the truck benefits from a controlled engine temperature from the liquid cooling, the HD does not and it can swing pretty hot. On top of that, combustion chamber shape and other factors will allow certain engines to run lower octane with higher compression. The truck and the HD are apples and oranges for the octane discussion.
Last edited by Ed Ramberger; Jan 29, 2021 at 04:45 PM.
Advanced
Joined: Nov 2015
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From: Spring Grove, IL
The last trip I did, it was mid-30's to mid-50's at the point that 87 octane was the only option.
Cruiser
Joined: Jul 2010
Posts: 239
Likes: 42
What a KLR!
The original question is something that I've wondered about as well. I do run the higher octane in my bike as recommended. What gets me thinking is how bad is it to run a lower octane?
When I did my trip to Alaska a few years ago, most of the gas I could buy at some point was 87 octane. There wasn't even an 89 octane option. I had a KLR650, so I never worried about it, but, I often think of doing another Alaska trip on my Harley. I know people do similar trips on Harleys, so is it all that bad to run 87 octane through a few tanks of gas? Will I lessen the length of life of the engine?
I'm guessing there isn't a hard and fast answer.
When I did my trip to Alaska a few years ago, most of the gas I could buy at some point was 87 octane. There wasn't even an 89 octane option. I had a KLR650, so I never worried about it, but, I often think of doing another Alaska trip on my Harley. I know people do similar trips on Harleys, so is it all that bad to run 87 octane through a few tanks of gas? Will I lessen the length of life of the engine?
I'm guessing there isn't a hard and fast answer.
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While well intentioned I am sure, this is not good advice regarding ethanol fuel. I would advise reading up on phase separation and the hydrophilic nature of ethanol. I would never advise someone to leave ethanol fuel in a tank for a year. That is truly asking for trouble.