87 vs 93 Octane

[Gros Ventre]

"In theory it should gain some on 93 vs 91, but likely very marginal at best." False. The theory of these Otto Cycle engines says simply there is no gain in power output for octane higher than the design octane for the engine. So unless Ford designed it to take advantage of something higher than 91 octane (and maybe they did but I find no evidence of that), there is no gain in power output. That's the theory plain and simple and alcohol doesn't make a difference. It is a common fallacy that higher octane means higher power output. Simply untrue. The higher power output for higher octane only applies if the engine (principally compression ratio) was designed to utilize that octane. Like it or not that's the theory.

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[JExpedition07]

"In theory it should gain some on 93 vs 91, but likely very marginal at best." False. The theory of these Otto Cycle engines says simply there is no gain in power output for octane higher than the design octane for the engine. So unless Ford designed it to take advantage of something higher than 91 octane (and maybe they did but I find no evidence of that), there is no gain in power output. That's the theory plain and simple and alcohol doesn't make a difference. It is a common fallacy that higher octane means higher power output. Simply untrue. The higher power output for higher octane only applies if the engine (principally compression ratio) was designed to utilize that octane. Like it or not that's the theory.

Well Fords V8 engine program manager disagrees with you, he states several times on the record that the F-150 5.0 gains an additional 15 horsepower and 20 lb ft of torque on E-85 vs 91 octane. Take it up with Fords engineers ?. Several real world dyno runs done that echo what he states, and what I state here. Even the old 5.4L 3V gained power on E-85, it went from 310 to 320 horsepower and 365 lb ft to 390 lb ft. You fail to understand what Ti-VCT and modern controls are capable of when coupled with high compression. This isn’t 1965, they called and want their logic back.

 

[fordtruckman2003]

Years of running premium in a 3.5 Eco with better milage and more power on the butt dyno. Good enough reason for me to run premium on the 2.7 I have now.

 

[Gros Ventre]

Well, your butt dyno may lead you there, but it doesn't get the theory correct either. There are lots of reasons various dyno results may vary. If you want to talk of the engine design features I'm all ears... Yet the theory of the basic Otto Cycle engine is straightforward: The engine is designed for a certain maximum octane and if you use higher than that you are just pouring money out the tailpipe. I understand that for many reasons any given engine will run better on a certain fuel, I got it. On the other hand across many vehicles, I have run them on the least costly fuel I could find: they all ran just fine for the life of the engine to include a GM 350 cubic inch V-8 I ran for 30 years. On that GM engine I ran an experiment where I changed to a different type spark plug every 50,000 miles and could not discern any difference in performance/fuel consumption. So tell me what features enable use of higher octane...

 

[Snakebitten]

93 gets you different timing advance tables than 91 does. At least on the 3.5 Ecoboost it does. 91 will not max out OAR, therefore it's leaving timing on the table.

Every degree of advanced timing yields increase in HP.

I'm not claiming how noticeable it might be with a butt dyno. But the PCM will absolutely report (PID) the reduction in knock sensor input, the increase in OAR (octane adjust value), and the total advance timing in degrees.

 

[bgalakazam]

in Germany (and Europe in general), there is only ‘premium’ and more premium. 91-93. I do get to pick between E10 and E5. E10 is cheaper and has less mpg for me. Nothing surprising. I vaguely recall that engineer youtube guy doing a video with math and E30 came at the sweetspot for performance and mpg.

 

[Gooner5643]

Just ran my first tank of 93 coming from only ever running e85. It does feel slower to me. I also run an ngauge to watch some parameters and have knock as one of them. I’ve noticed on e85 it’s almost always 0 to -1.0 degrees. Where on 93 octane it’s anywhere from 0 to -5.5 degrees. Which is backwards of what you’d think since negative knock means it’s adding timing. So I’d assume it adjusts the “base” timing off of alcohol percentage and then adjusts plus or minus from there. ?‍

 

[JExpedition07]

Well, your butt dyno may lead you there, but it doesn't get the theory correct either. There are lots of reasons various dyno results may vary. If you want to talk of the engine design features I'm all ears... Yet the theory of the basic Otto Cycle engine is straightforward: The engine is designed for a certain maximum octane and if you use higher than that you are just pouring money out the tailpipe. I understand that for many reasons any given engine will run better on a certain fuel, I got it. On the other hand across many vehicles, I have run them on the least costly fuel I could find: they all ran just fine for the life of the engine to include a GM 350 cubic inch V-8 I ran for 30 years. On that GM engine I ran an experiment where I changed to a different type spark plug every 50,000 miles and could not discern any difference in performance/fuel consumption. So tell me what features enable use of higher octane...

Compression ratio.

Dude, your logic is so severely outdated to the point that it’s pure misinformation when applied to this engine. Sorry but if you wanted a simple Otto Atkinson cycle V8 you needed to buy a GM small block. The Ford 5.0 is not that engine. The 350 you keep referring to has a single cam in block and an 8.5:1 compression ratio with a carburetor and distributor.

The 5.0 is 12:1 compression and is a dual overhead cam engine with Ti-VCT which can vary the degree of advance or retard of the intake and exhaust valves independently and on the fly. You have to swap the entire camshaft with a new one on the 350 to vary the valve actuation from stock, and still cannot vary the intake and exhaust independently like the 5.0 can on the fly. The 5.0 has PFDI with port fuel delivery and direct injection, meaning both a high pressure and low pressure delivery system. The engine varies which injectors are primary based on rpm, and changes the volume/delivery rate dependent on fuel used (E-85 requires higher volume). Lastly the 5.0 uses modern knock sensing to pull timing on low octane fuels, if it does not sense knock (running premium) it will allow ignition (spark) to advance. If you put 12:1 compression pistons in that 350 you keep talking about you’d be running race fuel so it didn’t pre-detonate and grenade a piston through the oil pan lol.

 

[Gros Ventre]

Trouble is you're wrong. The atkinson cycle is a different engine than an Otto cycle. Nothing I've said is out of date. It is the theory of the engine in your F150. I'm well aware of the differences between my GM 350 and more modern engines. Come on, it's a '92 and isn't even an OBD-II. Increasing compression ratio is the feature of design that enables extraction of more power out of fuel with a higher octane rating. The theory is straight forward: a gas engine becomes more efficient than a diesel engine with a high enough compression ratio... it's just that the cost of that octane rated fuel is too high... So how do theyuse 87 octane in a 10.5:1 engine? Well... that thing called gasoline direct injection is the basic element that sidesteps detonation problems... Think that might be related? All heresy begines with grains of truth and that's what you're doing. C YA...

 

[JExpedition07]

Trouble is you're wrong. The atkinson cycle is a different engine than an Otto cycle. Nothing I've said is out of date. It is the theory of the engine in your F150. I'm well aware of the differences between my GM 350 and more modern engines. Come on, it's a '92 and isn't even an OBD-II. Increasing compression ratio is the feature of design that enables extraction of more power out of fuel with a higher octane rating. The theory is straight forward: a gas engine becomes more efficient than a diesel engine with a high enough compression ratio... it's just that the cost of that octane rated fuel is too high... So how do theyuse 87 octane in a 10.5:1 engine? Well... that thing called gasoline direct injection is the basic element that sidesteps detonation problems... Think that might be related? All heresy begines with grains of truth and that's what you're doing. C YA...

Just wanted to put this in the open air, this guy thinks he knows more about engines than the guys who designed the engines for Ford, got it


“The new 2011 5.0 is rated at 360 horsepower (at 5,500 rpm) and 380 pounds-feet of torque (at 4,250 rpm) running on regular unleaded gasoline. It’s positioned as the midrange, high-volume engine choice for the F-150, below the more powerful 3.5-liter EcoBoost V-6 (365 hp and 420 pounds-feet of torque) and conventional large-displacement 6.2-liter V-8 (411 hp and 434 pounds-feet of torque).

But the 5.0 is also flex-fuel capable. Flexible-fuel vehicles are designed to run on gasoline or a blend of up to 85 percent ethanol (E85).

Burning E85 fuel boosts 5.0 engine power to 375 hp and 390 pounds-feet of torque, said Mike Harrison, Ford’s program manager for V-8 engines.”

 

[JExpedition07]

Straight from my digital owners manual for my 2023 5.0 F-150

 

[slow3v]

If you get on the throttle you’ll notice, I am a lead foot. Stock dynos show 330 rwhp on 87 and 350-360 rwhp on 93. You’ll feel that at full throttle. The 5.0L’s 12.0:1 compression to too high for 87 to not pre-ignite, so it retards timing on 87 especially when mashing the throttle or towing. You can run 87 just fine all the time, but there is a power loss factor. It should not affect efficiency, just horsepower.

This is factual.

 

[Samson16]

I have a 3.31:1 axle ratio in tenth gear at 80 mph the rpm is just under 1750, barely above a fast idle at 80. My previous 150 5.0 had a 3 53: rear and with the 6 speed in top gear at 80 it was running about 2300 rpm. Never got more than 18 mph with that truck using 93 octane.

That's what surprises me about my PB running 93. How in the world do I get above 21mpg doing 80mph with a 3.73 rear end? It feels like I've thrown a saddle on a Unicorn.

 

[Big Dog Daddy]

That's what surprises me about my PB running 93. How in the world do I get above 21mpg doing 80mph with a 3.73 rear end? It feels like I've thrown a saddle on a Unicorn.

I've always ordered my trucks with low rear end ratios, (higher numerically), well, because it's a truck. But I never pull a trailer. So when I ordered this truck, I thought to myself let's make it an interstate cruiser and went with the 3.31 rear, and I've found it to be great at highway speeds with the 10r80.
With the 3 31 if you calculate out the ratios with the 10R80, I ended up with a lower 1st gear than I had with the old truck 5 0/ 6R80/ 3 53 rear. And a higher top ratio than the 6r80 do to the 3 overdrive gears in the 10R80. I'm very happy with the choice of the 3.31

 

[Samson16]

I'd say that's a real world performance upgrade right there!

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