Why do we need 91 or higher octane?
Thread Starter
|
Tourer
Joined: Apr 2020
Posts: 490
Likes: 271
From: PNW
Why do we need 91 or higher octane?
I own 2 Harleys: 2019 48 Special and a 2017 Wide Glide 103HO stage 1. Both bikes "require" 91 or higher. Now with the progtards in charge the war on oil and gas will once again heat up which means gas will hit at least $5/gal very soon and we're over $3 already in the soviet northwest. We don't have 91 here just 92 or 93 so I have to use the most expensive gas around. With every fill getting more painful, I have to ask why we need 91.
I understand octane ratings and have run a 1999 Dodge 318 Ram as a daily driver since 2001 which doesn't have knock sensors so I've learned a lot about gas, tuning, and octane requirements over 20 years. But my Dad has never run higher than 87 in his 02 88 Heritage and all my biker friends (non-HD) only use 87 in their Suzukis, Kawasakis, and Hondas. And none of their bikes are older than 5 years. So why on such low compression, air cooled, antique, tractor motors like these do we need high octane? I could kind of understand on my Dyna with the Stage 1 and tune needing higher octane, but at least on the Sporty EVO it shouldn't, right? What's the deal here? Thanks for any input.
I understand octane ratings and have run a 1999 Dodge 318 Ram as a daily driver since 2001 which doesn't have knock sensors so I've learned a lot about gas, tuning, and octane requirements over 20 years. But my Dad has never run higher than 87 in his 02 88 Heritage and all my biker friends (non-HD) only use 87 in their Suzukis, Kawasakis, and Hondas. And none of their bikes are older than 5 years. So why on such low compression, air cooled, antique, tractor motors like these do we need high octane? I could kind of understand on my Dyna with the Stage 1 and tune needing higher octane, but at least on the Sporty EVO it shouldn't, right? What's the deal here? Thanks for any input.
Popular Reply
Jan 29, 2021, 11:51 AM
Seasoned HDF Member
Joined: Sep 2009
Posts: 17,148
Likes: 6,171
From: SE Michigan
All we have here is 86, 89, or 93. So I use 93. The difference in cost is so small with a Harley tank I never even think about it.
The reason for 91 requirement is compression ratio. Octane is a measure of resistance to ignition, so the more compression you have, the higher octane you would need. Harley's run north of 10:1 these days, thus the requirement.
I noted your comments about other bikes, and makes, but Harley recommends it, so I use it. Again, worrying about the cost difference is silly.
The reason for 91 requirement is compression ratio. Octane is a measure of resistance to ignition, so the more compression you have, the higher octane you would need. Harley's run north of 10:1 these days, thus the requirement.
I noted your comments about other bikes, and makes, but Harley recommends it, so I use it. Again, worrying about the cost difference is silly.
Seasoned HDF Member
Joined: Sep 2009
Posts: 17,148
Likes: 6,171
From: SE Michigan
All we have here is 86, 89, or 93. So I use 93. The difference in cost is so small with a Harley tank I never even think about it.
The reason for 91 requirement is compression ratio. Octane is a measure of resistance to ignition, so the more compression you have, the higher octane you would need. Harley's run north of 10:1 these days, thus the requirement.
I noted your comments about other bikes, and makes, but Harley recommends it, so I use it. Again, worrying about the cost difference is silly.
The reason for 91 requirement is compression ratio. Octane is a measure of resistance to ignition, so the more compression you have, the higher octane you would need. Harley's run north of 10:1 these days, thus the requirement.
I noted your comments about other bikes, and makes, but Harley recommends it, so I use it. Again, worrying about the cost difference is silly.
Seasoned HDF Member
Joined: Feb 2008
Posts: 23,001
Likes: 11,441
All we have here is 86, 89, or 93. So I use 93. The difference in cost is so small with a Harley tank I never even think about it.
The reason for 91 requirement is compression ratio. Octane is a measure of resistance to ignition, so the more compression you have, the higher octane you would need. Harley's run north of 10:1 these days, thus the requirement.
I noted your comments about other bikes, and makes, but Harley recommends it, so I use it. Again, worrying about the cost difference is silly.
The reason for 91 requirement is compression ratio. Octane is a measure of resistance to ignition, so the more compression you have, the higher octane you would need. Harley's run north of 10:1 these days, thus the requirement.
I noted your comments about other bikes, and makes, but Harley recommends it, so I use it. Again, worrying about the cost difference is silly.
My 1996 Harley is designed to and runs great on 87 octane. But in the quest for more power those days ended.
Seasoned HDF Member
Joined: Jun 2019
Posts: 10,036
Likes: 10,767
From: SE Michigan
the answer to why you need higher octane?
simple answer: the higher the octane, the lower the chance of uncontrolled or mistimed combustion
when your vehicle doesn't need high octane, then use cheap gas....there is zero benefit to using the higher octane option...(the exception being that some suppliers only put detergents in the good stuff, in that case, it's worth it to buy the expensive stuff to get the detergents too).....when a vehicle calls for premium only, use premium only
not sure if's all HDs, but mine calls for the good stuff....and that's all it gets....when your vehicle calls for premium, it's because when tested, it tested significantly worse when fueled by low octane fuel
simple answer: the higher the octane, the lower the chance of uncontrolled or mistimed combustion
when your vehicle doesn't need high octane, then use cheap gas....there is zero benefit to using the higher octane option...(the exception being that some suppliers only put detergents in the good stuff, in that case, it's worth it to buy the expensive stuff to get the detergents too).....when a vehicle calls for premium only, use premium only
not sure if's all HDs, but mine calls for the good stuff....and that's all it gets....when your vehicle calls for premium, it's because when tested, it tested significantly worse when fueled by low octane fuel
Trending Topics
Seasoned HDF Member
Joined: Aug 2014
Posts: 35,239
Likes: 19,070
From: 40.2444° N, 75.6419° W
the answer to why you need higher octane?
simple answer: the higher the octane, the lower the chance of uncontrolled or mistimed combustion
when your vehicle doesn't need high octane, then use cheap gas....there is zero benefit to using the higher octane option...(the exception being that some suppliers only put detergents in the good stuff, in that case, it's worth it to buy the expensive stuff to get the detergents too).....when a vehicle calls for premium only, use premium only
not sure if's all HDs, but mine calls for the good stuff....and that's all it gets....when your vehicle calls for premium, it's because when tested, it tested significantly worse when fueled by low octane fuel
simple answer: the higher the octane, the lower the chance of uncontrolled or mistimed combustion
when your vehicle doesn't need high octane, then use cheap gas....there is zero benefit to using the higher octane option...(the exception being that some suppliers only put detergents in the good stuff, in that case, it's worth it to buy the expensive stuff to get the detergents too).....when a vehicle calls for premium only, use premium only
not sure if's all HDs, but mine calls for the good stuff....and that's all it gets....when your vehicle calls for premium, it's because when tested, it tested significantly worse when fueled by low octane fuel
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
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,614
Likes: 6,440
From: Honah Lee
My 04 calls for it. I really don't need it on the coast. You just need to drive like a little old lady going to church on Sunday. Stay in the correct gear and throttle slow enough for the timing and air fuel rate mixture to keep up. Mine never pings.
I have gotten as high as 51 MPG. I can get it down to high 30s MPG driving frisky and of course needs premium . Premium has same BTU or power as regular. Premium has additives to raise flash point and burn slower. Regular will explode WOT it too quickly under load. That rattles valve seats, pistons bottom end. Once in a while won't hurt it.
I have gotten as high as 51 MPG. I can get it down to high 30s MPG driving frisky and of course needs premium . Premium has same BTU or power as regular. Premium has additives to raise flash point and burn slower. Regular will explode WOT it too quickly under load. That rattles valve seats, pistons bottom end. Once in a while won't hurt it.
Last edited by Jackie Paper; Jan 29, 2021 at 12:43 PM.
Seasoned HDF Member
Joined: May 2017
Posts: 5,915
Likes: 5,929
From: NorCal
My 04 calls for it. I really don't need it on the coast. You just need to drive like a little old lady going to church on Sunday. Stay in the correct gear and throttle slow enough for the timing and air fuel rate mixture to keep up. Mine never pings.
I have gotten as high as 51 MPG. I can get it down to high 30s MPG driving frisky and of course needs premium . Premium has same BTU or power as regular. Premium has additives to raise flash point and burn slower. Regular will explode WOT it too quickly under load. That rattles valve seats, pistons bottom end. Once in a while won't hurt it.
I have gotten as high as 51 MPG. I can get it down to high 30s MPG driving frisky and of course needs premium . Premium has same BTU or power as regular. Premium has additives to raise flash point and burn slower. Regular will explode WOT it too quickly under load. That rattles valve seats, pistons bottom end. Once in a while won't hurt it.