87 vs 93 Octane

[DBL R]

Essentially any modern day forced induction vehicle should be considered a performance engine and should run at least 91 octane. Even the ford manual says to use the higher octane when towing and during other events with “high demand” since 87 octane will produce less power. These ecoboost engines make more horsepower per liter than some modern day Porsche’s. Running anything under 91 octane is just shooting yourself in the foot.

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[Calson]

The problem is in thinking that octane rating equals power rating and it does not. Octane rating is a measure of knock or pre-ignition resistance of the fuel and nothing more. If a lower octane rated than is recommended fuel is used the spark advance is reduced to minimize pre-ignition or engine knocking. This reduces the power produced by the engine. But is a higher than recommended octane rated gas is used there is no gain and just as much fuel will be burned.

The only exception is with engines with many hours of operation that may have carbon buildup on the head(s) and this can make an engine more prone to pre-ignition when raw gas is injected. But this scenario is highly unlikely.

Not rocket science and octane rating has been around for 100 years and nothing has changed.

 

[Gros Ventre]

R

The problem is in thinking that octane rating equals power rating and it does not. Octane rating is a measure of knock or pre-ignition resistance of the fuel and nothing more. If a lower octane rated than is recommended fuel is used the spark advance is reduced to minimize pre-ignition or engine knocking. This reduces the power produced by the engine. But is a higher than recommended octane rated gas is used there is no gain and just as much fuel will be burned.

The only exception is with engines with many hours of operation that may have carbon buildup on the head(s) and this can make an engine more prone to pre-ignition when raw gas is injected. But this scenario is highly unlikely.

Not rocket science and octane rating has been around for 100 years and nothing has changed.

Right on!

 

[Gros Ventre]

R

Right on!

Note that a badly carboned up engine effectively raises the compression ratio...

 

[Samson16]

I’m always 93. My trucks runs noticeably better with it. Costco or QT always has it at a good price. There’s a subtle change with 87 that’s noticing when you need to put your foot down.

Wanna know what really made my truck come alive? 0 eth 93 octane. They sell it at Buccees in Galveston.

Back in the early eighties you could buy all kinds of stuff in Galveston. Just sayin'

I had my hand-me-down '76 Pinto stolen off the beach in Galveston. Never try the old hide the keys on the tire trick by the way. Thieves are wise to that one...

 

[amschind]

After reading much in here on the "Octane Question," I have drawn the conclusion that the engine is designed for 91 octane fuel. An Otto Cycle engine such as this is, cannot extract more power out of its fuel than the octane rating it is designed for. In order to gain the "benefit" of specifying 87 octane in literature and sales, they then used the electronics to derate the engine to run on 87 octane. So will it produce more power on 93 vs 91 octane? No. Will it produce more power on 91 vs 87 octane? In all likelihood: Yes. Would there be a difference in performance of the 5.0L normally aspirated engine vs the 3.5L turbocharged engine for equal power output levels? Yes. But, when designers set out to prevent detonation in a turbocharged engine, they richen the mixture up relative to what a normally aspirated engine would need for the same power output. So the fuel consumption of the turbo engine would likely be higher for the same power output.

I think this is correct.

 

[Samson16]

I think this is correct.

"I have drawn the conclusion that the engine is designed for 91 octane."

That's his opinion and I have no idea if he's correct or not but I think one would have to continue increasing the octane rating of the fuel until the upper limit of the timing tables is reached. Any further octane rating increase will have little to no effect.

 

[Snakebitten]

"I have drawn the conclusion that the engine is designed for 91 octane."

That's his opinion and I have no idea if he's correct or not but I think one would have to continue increasing the octane rating of the fuel until the upper limit of the timing tables is reached. Any further octane rating increase will have little to no effect.

Smarty pants. ?

Ok, that would be true for the stock oem calibration.
But then you can "tune" the truck in an effort to increase the timing by editing the timing tables. That's why it's fairly easy to fetch as much as 100HP that Ford has left on the table on the 3.5 Ecoboost.
OEM boost at sea level is ~18psi
OAR maxes out at ~93 octane level, so the timing table for max OAR is the limit.

Throw some E30, E50,.....and now you can increase timing/boost beyond the oem caps.

Of course you are now taxing various components at a load-level that Ford intentionally didn't. But there's now more than a decade of trial & error to draw on if you want to play.

More "octane", or more anti-knock the fuel is, the more power you can extract from the same 3.5 liters. That Ecoboost has some seriously awesome engine management behind it.

 

[Samson16]

I've admired the Ford 3.5L long before I owned one.

I give you the 2022 GT specs:

Specifications

PRICE AS TESTED: $525,750 (base price: $478,750)
ENGINE TYPE: twin-turbocharged and intercooled Miller-capable V-6, aluminum block and heads
Displacement: 213 cu in, 3497 cc
Power: 647 hp @ 6250 rpm
Torque: 550 lb-ft @ 5900 rpm
TRANSMISSION: 7-speed dual-clutch automatic with manual shifting mode
DIMENSIONS:
Wheelbase: 106.7 in
Length: 187.5 in
Width: 78.9 in Height: 43.7 in
Passenger volume: 43 cu ft
Cargo volume: 0.4 cu ft
Curb weight: 3381 lb
C/D TEST RESULTS:
Zero to 60 mph: 3.0 sec
Zero to 100 mph: 6.2 sec
Zero to 130 mph: 10.1 sec
Zero to 150 mph: 14.5 sec
Zero to 170 mph: 21.4 sec
Rolling start, 5-60 mph: 3.6 sec
Top gear, 30-50 mph: 2.3 sec
Top gear, 50-70 mph: 2.3 sec
Standing ¼-mile: 10.8 sec @ 134 mph
Top speed (drag limited, mfr's claim): 216 mph
Braking, 70-0 mph: 145 ft
Roadholding, 300-ft-dia skidpad: 1.11 g
FUEL ECONOMY:
EPA combined/city/hwy: 14/11/18 mpg

 

[Gros Ventre]

Smarty pants. ?

Ok, that would be true for the stock oem calibration.
But then you can "tune" the truck in an effort to increase the timing by editing the timing tables. That's why it's fairly easy to fetch as much as 100HP that Ford has left on the table on the 3.5 Ecoboost.
OEM boost at sea level is ~18psi
OAR maxes out at ~93 octane level, so the timing table for max OAR is the limit.

Throw some E30, E50,.....and now you can increase timing/boost beyond the oem caps.

Of course you are now taxing various components at a load-level that Ford intentionally didn't. But there's now more than a decade of trial & error to draw on if you want to play.

More "octane", or more anti-knock the fuel is, the more power you can extract from the same 3.5 liters. That Ecoboost has some seriously awesome engine management behind it.

Well, we still disagree... In the theoretical cycle of intake, compression, ignition & expansion, then exhaust there is a design point beyond which higher octane does nothing for you. But the key for this engine is that the compression stroke does not contain a significant amount of fuel with the air charge. Hence, there is little chance of premature ignition. The role of Gasoline Direct Injection enabling higher compression beyond the design point of the octane rating of its fuel is a major feature of this engine. Why would Ford split for the cost and complexity of the GDI setup? I believe precisely because it sidesteps that fundamental element of the thermodynamic cycle.

 

[Snakebitten]

Well, we still disagree...

And yet there's still a harmony in the universe that we both exist in simultaneously.

 

[JExpedition07]

Folks….the 5.0 V8 is rated on premium fuel per the ASE standard. That does not mean Ford does not leave timing on the table for octane beyond a rating of 91. E-85 quite literally creates more power on the 5.0 on the stock calibration than 93 octane. This is confirmed by Ford in several instances, and every single dyno you can find.

Here the 5.0 makes 385 rear wheel horsepower and 423 lb ft of torque at the wheel post tune. There has been no hardware change to the engine, Livernois has simply extracted power left on the table. Take a gander at their 93 octane tune, it’s not quite as powerful as the E-85 one shown here.

 

[JExpedition07]

Maybe you should take a breath.....

I did get a little too hot, but this is the equivalent to arguing with a flat earther. When you have a plethora of information from published sources, including the creator of the product and someone says “no, the facts are all wrong” it’s quite infuriating

 

[WhiteLightningnshitshadow]

The intake valves can indeed be left open longer.


semi related question, we all know ford doesn't recommend E85 or even 10% 85 in Ecoboost engines. What is the actual tested lower limit of what the antiknock mechanisms can account for?

 

[Samson16]

Folks….the 5.0 V8 is rated on premium fuel per the ASE standard. That does not mean Ford does not leave timing on the table for octane beyond a rating of 91. E-85 quite literally creates more power on the 5.0 on the stock calibration than 93 octane. This is confirmed by Ford in several instances, and every single dyno you can find.

Here the 5.0 makes 385 rear wheel horsepower and 423 lb ft of torque at the wheel post tune. There has been no hardware change to the engine, Livernois has simply extracted power left on the table. Take a gander at their 93 octane tune, it’s not quite as powerful as the E-85 one shown here.

The Powerboost tune just keeps looking better!

492HP and 594TQ

Let's snap some axles and shear some bolts!

Even Otto and his cycle can come along for the ride. Plenty of room in back

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