octane rating and engine performance

We like to think that the engine can compensate for poor choices in fuel, but forget that the compression ratio cannot be adjusted. The Ecoboost engine is just one example of turbocharged engines that must lower boost, again to compensate for low octane fuels.

I don't know how Ford should write a manual, because even limiting words to non-technical confuses the masses.

He is also purposely leaving out a very important part of that 91 octane recommendation. It specifically states.

"For best overall vehicle and engine
performance, premium fuel with an octane
rating of 91 or higher is recommended."

Meaning that if you want/need the added 5% or so of horsepower output which is the best performance of that engine, then 91 or higher is recommended. Many Ford engines have different horsepower output numbers depending on the octane used.

My wife's N/A 3.5L Infiniti is the same way it is about 310 hp on 91 octane and around 290 hp on regular. However, the recommendation is reverse for her car. It states that 91 is recommended, but can run on lower octane with less performance.

Lynnmor wrote:
If one cannot even understand this phrase: "premium fuel with an octane rating of 91 or higher is recommended" why even print a manual?

It's a conspiracy to get you to spend more money on fuel. No, not really.

Really not much of a difference between them when written into any specification and/or manual

Goes to both warranty and liability

If it is 'recommended' and you don't follow that recommenation and something happens...why would they be obligated to provide warranty?

Ditto 'required'...same thing as above, but more forceful in verbiage...

PS...since most vehicles today are computer controlled everything...it can change timing on the fly to protect itself

Plus, towing heavy is way different than driving around town shopping without towing heavy.

The margin for octane requirement is very different in those two applications/usage.

Has to do with duty cycle...

womps wrote:

Lynnmor wrote:
I guess Ford gave up on trying to explain to users how a turbocharged engine produces high cylinder pressures and should have premium fuel to prevent knocking. Since folks will disregard any kind of advice and use whatever is cheap, all they can do is write a generic owners manual and provide safeguards to prevent engine damage from low octane fuel. If one cannot even understand this phrase: "premium fuel with an octane
rating of 91 or higher is recommended" why even print a manual?

Because there is a difference between “recommended” and “required”.

Lynnmor wrote:
I guess Ford gave up on trying to explain to users how a turbocharged engine produces high cylinder pressures and should have premium fuel to prevent knocking. Since folks will disregard any kind of advice and use whatever is cheap, all they can do is write a generic owners manual and provide safeguards to prevent engine damage from low octane fuel. If one cannot even understand this phrase: "premium fuel with an octane
rating of 91 or higher is recommended" why even print a manual?

Because there is a difference between “recommended” and “required”.

Lessmore wrote:
Even back in the '90's when we were towing with a '76 Chevy 350 cube V8 and a '97 Vortec 4300 V6...when we towed I would put premium fuel (91 octane). Other than that I would use Regular (87 octane) for everyday driving. Either way I never noticed any engine knocking or pinging. The newer Vortec automatically adjusted it's timing and /or knock sensor and compensated for lower octane gas. I'm pretty sure the '97 manual (Vortec V6) recommended high test gas when towing and that's what I filled up with, towing.

Exactly! I don't think it is just an Ecoboost thing and is mainly for dual fuel engines that can alter their ignition and valve timing for different fuels depends on how much knock is detected. Where people think this is only an Ecoboost thing I have no idea. My wife's non turbocharged Infiniti SUV says something similar in her owners manual.

Even back in the '90's when we were towing with a '76 Chevy 350 cube V8 and a '97 Vortec 4300 V6...when we towed I would put premium fuel (91 octane). Other than that I would use Regular (87 octane) for everyday driving. Either way I never noticed any engine knocking or pinging. The newer Vortec automatically adjusted it's timing and /or knock sensor and compensated for lower octane gas. I'm pretty sure the '97 manual (Vortec V6) recommended high test gas when towing and that's what I filled up with, towing.

I guess Ford gave up on trying to explain to users how a turbocharged engine produces high cylinder pressures and should have premium fuel to prevent knocking. Since folks will disregard any kind of advice and use whatever is cheap, all they can do is write a generic owners manual and provide safeguards to prevent engine damage from low octane fuel. If one cannot even understand this phrase: "premium fuel with an octane
rating of 91 or higher is recommended" why even print a manual?

They say the exact same thing about the 6.2L in the Superduty.

Page 188... 2018 SUPER DUTY Owner’s Manual

The 5.0L and 3.0L in the F150.

Pages 181-182...2018 F-150 Owner’s Manual

All of the engines in the Explorer(both Ecoboost and non-Ecoboost)

Pages 173-175...2018 EXPLORER Owner’s Manual

Even on the cars like the Fusion.

Page 154-155...2018 Fusion Owner’s Manual



They say the same exact thing you posted for every engine even in vehicles that are not meant to tow.

Lynnmor wrote:

ShinerBock wrote:

Lynnmor wrote:


Many engines are turbocharged today and the elevation makes little difference in fuel requirements. The OP has a 5.0 non-turbocharged so the low octane should be OK, but Ford Ecoboost engines should have premium fuel when towing, per the owners manual.

I don't think the manual says you should have it when towing. It says the same thing it states for all their duel fuel engines that can increase power output with higher octane fuel which is to add higher octane fuel if you want more performance and will more more noticeable in situations like towing. It states this for the 5.0, 6.2, and just about every other engine they make.

Here is a direct copy & paste from the owners manual:

Your vehicle is designed to operate on
regular unleaded gasoline with a minimum
pump (R+M)/2 octane rating of 87.
Some fuel stations, particularly those in
high altitude areas, offer fuels posted as
regular unleaded gasoline with an octane
rating below 87. We do not recommend
these fuels.
For best overall vehicle and engine
performance, premium fuel with an octane
rating of 91 or higher is recommended. The
performance gained by using premium fuel
is most noticeable in hot weather as well
as other conditions, for example when
towing a trailer.

That is the same thing they state for all of their duel fuel engines that can adjust power output depending on octane rating. I don't see anywhere where ford states you should run 91 octane when towing like you said. I only see where that state that if you want the best overall performance out of the engine then higher octane is recommended and it will be more noticeable during towing situations like I said. It never says you should.