Why is 91 Octane Recommended?
Cruiser
Joined: Aug 2008
Posts: 190
Likes: 25
From: Rotterdam, Netherlands
91 octane, on what scale? I can't make head nor tail from the US octane numbers. Basically its an average between RON and MON, sometimes called PON, and 87 MON and 91 PON are both 95 RON.
So 91 may be just the lowest octane fuel that you can get your hands one if its PON, and the highest if its MON.
Strange world...
So 91 may be just the lowest octane fuel that you can get your hands one if its PON, and the highest if its MON.
Strange world...
Last edited by Daedalus; Aug 1, 2018 at 11:43 AM.
Grand HDF Member
Joined: Jun 2007
Posts: 4,264
Likes: 690
From: WESTERN CHICAGO AREA
If the manual says recommended = use 87, 89, or 91 whatever works., if it says required = you must use 91
I've used 87 in all my Harleys and a couple of Vettes. Not one fuel related problem in over 50 years.
If you have a hi performance or modified bike or your engine pings - use 91. Tooling around town or on the highway = 87 is fine
I've used 87 in all my Harleys and a couple of Vettes. Not one fuel related problem in over 50 years.
If you have a hi performance or modified bike or your engine pings - use 91. Tooling around town or on the highway = 87 is fine
Tourer
Joined: Jun 2018
Posts: 356
Likes: 47
From: freedom
lets be real....do the match....that doesnt equate to all that much extra expense over the course of a year. my bike idles better on premium and runs smoother. no pinging but it definitely runs smoother.
I use 91 or when I can find it 93. Manual for mine says to use 91 or higher, ran 87 once and the bike ran but not well.
Trending Topics
Seasoned HDF Member
Joined: May 2012
Posts: 32,934
Likes: 36,031
From: Carlsbad, CA
You may not notice it pinging on 87, because the antiknock system retards the spark when it detects pinging. And with that goes your performance.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Intermediate
Joined: Sep 2017
Posts: 35
Likes: 2
From: NY
There is no energy difference between different gasoline octane ratings Putting high octane in an engine that has not been designed for it results in no difference in power that the engine will produce.
Higher octane fuel can be subject to more heat and more compression before igniting with out a spark.
harley engines run HOT
Higher octane fuel can be subject to more heat and more compression before igniting with out a spark.
harley engines run HOT
Tourer
Joined: Jun 2018
Posts: 356
Likes: 47
From: freedom
what year bike do you have?? i know my 09 surely doesnt have a knock sensor so no antiknock system.