87 vs 91 Octane?

Will you be filling up using 87 or 91 octane moving forward?


  • Total voters
    249

tjbronco

Big Bend
Well-Known Member
First Name
Tim
Joined
Mar 19, 2022
Threads
4
Messages
98
Reaction score
135
Location
44118
Vehicle(s)
2022 Ford Bronco Sport, 2020 Subaru Outback
Not claiming to be the expert on this, but here goes...
I have had Turbo Saabs for many years. They had a knock sensor in the block that detected pre-detonation/engine knock - it is a closed loop system. On a Turbo, the higher the boost increases the effective compression ratio of the engine - so the higher the boost, the more likely it is for the engine to experience pre-detonation/knock. A higher octane gas will reduce pre-detonation and allows for a higher compression ratio to be used in an engine. When the Saab computer would detect pre-detonation with the knock sensor, it would dial back the boost, to protect the engine, which would lower the maximum horsepower of the engine. The higher the octane gas you would use, the higher the boost level you could obtain due to less engine knock/pre-detonation detected - thus more horsepower. I would bet the Bronco turbo engine works on a similar principle, which is why higher octane fuel equals more ultimate horsepower. The newer engines in the Bronco also have direct injection, which lowers pre-detonation in the engine by only supplying fuel just in time, when it is to be combusted - so the engines in the Broncos can run higher compression ratios than older Turbo cars like my Saabs. The 1.5 Bronco engine actually has both direct fuel injection and port fuel injection - I heard it is to help protect the intake valves, which run dry of fuel in a direct injection only engine.
Sponsored

 

JAD67428

Outer Banks
Well-Known Member
First Name
Steve
Joined
Nov 21, 2021
Threads
17
Messages
664
Reaction score
1,123
Location
MA.
Vehicle(s)
2023 Ford Bronco Sport. 1994 Ford Mustang GT.
You're about to fill up your gas tank for the first time in your Bronco Sport.....will you be using 87 or 91 octane?
How about 93 Octane ??? That’s what I’ll be filling up with. 91 octane is a pain in the butt around my area to find, 93 octane is more abundant around me so I just use that.
 

Meanderthal

Badlands
Well-Known Member
First Name
Eric
Joined
Mar 19, 2022
Threads
10
Messages
2,008
Reaction score
2,760
Location
Colorado
Vehicle(s)
'08 BMW R1200 GS Adv, '23 Norden Expedition
How about 93 Octane ??? That’s what I’ll be filling up with. 91 octane is a pain in the butt around my area to find, 93 octane is more abundant around me so I just use that.
If there is any benefit in running 91 octane, there would be even more by running 93 octane.
 

Mark S.

Badlands
Well-Known Member
First Name
Mark
Joined
Oct 30, 2021
Threads
99
Messages
5,155
Reaction score
9,591
Location
St. Jacob, IL
Vehicle(s)
2021 Badlands | 2020 Escape
...pre-detonation/engine knock...
Detonation (knock) and pre-ignition are both forms of uncontrolled ignition, but they occur for very different reasons and with very different implications for engine longevity. Detonation is uncontrolled combustion AFTER the spark fires, and pre-ignition is uncontrolled ignition PRIOR to the spark firing.

Detonation is normal for Ford's EcoBoost engines. Indeed, detonation MUST occur for the computer to properly set boost, mixture and ignition timing to get the most power. Most engines can run indefinitely without deleterious effects under light detonation, and even heavy detonation for brief periods will not cause significant damage.

Pre-ignition, on the other hand, can destroy an engine in short order. This video explains the difference between the two phenomenon. After watching, it should be obvious why pre-ignition is so much worse than detonation.



On a Turbo, the higher the boost increases the effective compression ratio of the engine - so the higher the boost, the more likely it is for the engine to experience pre-detonation/knock.
It's about heat. Compressing things adds heat, and heat makes things ignite. Higher octane fuel has a higher ignition point, so the fuel/air mixture may be compressed more--and achieve a higher temperature during compression--without losing control of combustion.

When the Saab computer would detect pre-detonation with the knock sensor, it would dial back the boost, to protect the engine, which would lower the maximum horsepower of the engine. The higher the octane gas you would use, the higher the boost level you could obtain due to less engine knock/pre-detonation detected - thus more horsepower. I would bet the Bronco turbo engine works on a similar principle, which is why higher octane fuel equals more ultimate horsepower.
Mostly correct. It's not just boost the PCM (powertrain control module) alters, however, it's also mixture (the ratio of fuel and air) and ignition timing, with timing the most critical. Most don't realize that the spark fires while the piston is still traveling upward during the compression stroke (reference the video above). The goal is to get the most pressure pushing down on the cylinder for the longest time during the power stroke. Think of it like riding a bicycle. When you are pedaling a bicycle you must press on the pedal at just the right time. If you press too early then one foot is working against the other; if you press too late the pedal has already traveled too far down, reducing the time you get to push hard on it. That means less power going to the rear wheel. The PCM can do the same thing by altering ignition timing. By changing the timing you can significantly change the amount of pressure in the cylinder as well as the timing and duration of the push from the expanding gases. This will ultimately determine the amount of power the engine produces.

The 1.5 Bronco engine actually has both direct fuel injection and port fuel injection - I heard it is to help protect the intake valves, which run dry of fuel in a direct injection only engine.
While it's true that port injection is better at keeping intake valves free of carbon deposits, that's not the main reason Ford uses both port and direct injection on some of its engines.
 

bobdod

Badlands
Well-Known Member
Joined
Dec 9, 2021
Threads
0
Messages
133
Reaction score
232
Location
Colorado
Vehicle(s)
'22 Badlands Cyber Orange
Typically 85 is offered in higher-elevation regions. It is (or was) common here, but to be honest I'm not sure if that is still the case. I automatically grab the 91 handle to avoid ethanol, so I haven't noticed if 85 is still available. I think most are 87, 89 and 91 now.

Here's what the gub'mt says:

https://www.fueleconomy.gov/feg/octane.shtml#:~:text=In the U.S., unleaded gasoline,(more about that below).
Here in Denver and most all the rest of Colorado the standard I see is 85/87/89(or 91) as the options - so it's definitely still present. And, honestly I see most people, in all sorts of vehicles, reach for the 85 because we're all just used to hitting that leftmost button.
 


lemsip

Big Bend
New Member
First Name
Ed
Joined
May 16, 2022
Threads
0
Messages
4
Reaction score
2
Location
Colorado
Vehicle(s)
2021 Bronco Sport
Also in Denver and have always used 85 as it is considered regular. Is there any reason to take the 87 recommendation literally? or just consider it another way of saying regular? We live at 6k feet and drive to the mountains which are obviously higher.

we got ours used about a month ago. So far I have used mid grade 87, but I am planning to use 85. Is there any reason not to? We have the small engine. I do like to drive fast uphill in the mountains to pass the Subarus and tourons camped in the left lane. I do likE the acceleration it has, so maybe I should stick with mid grade.

If one were to try proper four wheeling, I imagine that the engine would really struggle without low range gearing, might that be another situation where higher grade petrol would help? Need to get rid of the shitty Michelins first though.
 

thekingprawn

Badlands
Well-Known Member
First Name
Dustin
Joined
Feb 27, 2022
Threads
12
Messages
1,584
Reaction score
2,117
Location
Kingston, Wa
Vehicle(s)
2022 Bronco Sport Badlands
I am planning to use 85. Is there any reason not to?
The manual specifically says not to. "Some fuel stations, particularly those in high altitude areas, offer fuels posted as regular unleaded gasoline with an octane rating below 87. The use of these fuels could result in engine damage that will not be covered by the vehicle warranty."
 

lemsip

Big Bend
New Member
First Name
Ed
Joined
May 16, 2022
Threads
0
Messages
4
Reaction score
2
Location
Colorado
Vehicle(s)
2021 Bronco Sport
Good to know. I will stick with 87.
Thank you.

The manual specifically says not to. "Some fuel stations, particularly those in high altitude areas, offer fuels posted as regular unleaded gasoline with an octane rating below 87. The use of these fuels could result in engine damage that will not be covered by the vehicle warranty."
 

Mark S.

Badlands
Well-Known Member
First Name
Mark
Joined
Oct 30, 2021
Threads
99
Messages
5,155
Reaction score
9,591
Location
St. Jacob, IL
Vehicle(s)
2021 Badlands | 2020 Escape
Good to know. I will stick with 87.
Thank you.
Lower octane is fine for normally aspirated (non-turbo) engines at altitude because as the air gets thinner they produce less power. Less power means less heat, which means lower risk of detonation. A turbocharger forces air into the cylinders, so the engine still gets enough air to produce the power and heat necessary to generate detonation. The min octane 87 fuel provides protection against detonation at all altitudes.
 


Mrmike

Outer Banks
Well-Known Member
First Name
Michael
Joined
Sep 18, 2022
Threads
48
Messages
708
Reaction score
794
Location
Syracuse, New York 13219
Vehicle(s)
'23 OBX, '20 Ecosport, '21 Kymco X-Town 300i
I'm old school and find it hard to believe that a motor with 11 to 1 compression ratio runs on 87 octane. Mine seems to be doing fine on it. After it's broke in, I'll try higher octanes to see if it runs any differently.
 

RSH

Badlands
Well-Known Member
First Name
Robert
Joined
Mar 23, 2021
Threads
1
Messages
910
Reaction score
1,055
Location
California
Vehicle(s)
Bronco Sport
My Badlands performs better with 91 octane. The engine runs smoother and is more responsive.
The owners manual also states for best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended.
I would think most anyone having a 1.5 model BS would want to get/have as much performance as possible and with people that rave about the 1.5 fuel economy, running premium fuel wouldn't really cost that much more.
 
Last edited:
  • Like
Reactions: ZQ8

Bucko

Outer Banks
Well-Known Member
First Name
Kevin
Joined
Mar 16, 2023
Threads
44
Messages
1,815
Reaction score
2,477
Location
Gainesville
Vehicle(s)
2023 Ford Bronco Sport
Mark S's post (#79) explains the potential need for octane fuel requirements.

For my simple mind, when I tow with the F-150, I fill up with 91 octane, as I'm towing a heavy camper or trailer, and need the extra power the fuel will provide.

On my BS, I don't plan to tow with it, nor explore off roading trails with it. The 87 octane I burn in it works fine around town, and at highway speeds I travel with it.
 

rocks

Outer Banks
Well-Known Member
First Name
Joe
Joined
Jun 12, 2023
Threads
33
Messages
896
Reaction score
1,138
Location
SC
Vehicle(s)
OBX, '23 HR-V EX-L wife's
I only go with 93 when I own a turbo engine vehicle.
 

Adam CW

Badlands
Well-Known Member
Joined
Apr 22, 2022
Threads
14
Messages
328
Reaction score
443
Location
Wisconsin
Vehicle(s)
2022 Bronco Sport Badlands
I always use ethanol-free 91 for the Badlands. I did the same with my 19 Escape 2.0.

93 is difficult to find around here.

I did try using 87 but saw a significant drop in fuel economy.
Sponsored

 
 




Top