87+ Octane Gas vs. 91+ - HELP

[BigMeatsBronco]

I think I've experimented with more fuel types than anyone here...I've used aviation fuel, E-85 mixed with clear gas, and tried high octane race fuel, and even used two stroke premix once when I ran out of fuel. the Broncos fueling system is VERY adaptive and can run on a WIDE range of octane from around 85 (in mexico) up to about 105 with effectiveness . the power differences are VERY noticeable between different fuels. I never buy 87. always get the highest octane available or a E-85 blend if possible.

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[BigMeatsBronco]

That would only make a difference if the 91-93 was actually 100% gas and not 10% ethanol. Some places that's true. Here, all the gas at all grades is 10% corn squeezins.

ethanol raises the octane tho.

 

[AZ_Liberty]

ethanol raises the octane tho.

Yes, but if you are storing and not using for a long time, you want real gas. Ethanol is hygroscopic.

 

[Shazamalingo]

I think I've experimented with more fuel types than anyone here...I've used aviation fuel, E-85 mixed with clear gas, and tried high octane race fuel, and even used two stroke premix once when I ran out of fuel. the Broncos fueling system is VERY adaptive and can run on a WIDE range of octane from around 85 (in mexico) up to about 105 with effectiveness . the power differences are VERY noticeable between different fuels. I never buy 87. always get the highest octane available or a E-85 blend if possible.

You have run E-85 in your Bronco?

 

[mpeugeot]

You have run E-85 in your Bronco?

And I have run 30% E-85 and 70% 93, makes for some hilarity when side by side with an ecoboost Mustang on the freeway... Confused as to why he can't pull a Bronco from 70-100 MPH.

 

[gerby151]

valves are simply not related to timing at all. In modern engines valves are related to engine speed.


no, your engine is better, not the gas.

Doing a little reading. It is still related to speed but not the way you meant with a timing chain connecting the crank to the camshaft
What Is A VVT-i Engine? (jdpower.com)

 

[gerby151]

ethanol raises the octane tho.

But in most cases the higher the ethanol content the lower the mpg (which for those of us with 2 doors means more stops). If the price point is great enough between the 2 it is a moot point on cost though.

 

[brkdncr]

I think we are talking past each other..... I will argue that absolutely valves and and pistons are timed.... The cam lobe opens the piston based on the position of the piston.... I think you would agree with that.... I am not saying anything you do not already know, obviously. But to me that is timing. No you can not change that timing. You are correct. The ignition is timed to spark based on what position those valves and piston are in. That is adjusted by the computer these days as opposed to the old school turning the distributer as you pointed out.

I think the only thing we are disagreeing on is the definition of "timing".

In the context of this discussion, knock and octane, I don't believe any engine adjusts valve timing or lift to reduce knock. I could be wrong, but most modern engines adjust valve timing and lift based on rpm through the use of variable cam lobes, or in cutting edge tech, independent actuators.

valves are timed - yes.
octane impacts valve timing - no.
octane impacts pre-det/knock. knock sensors communicate this to engine management, and ignition timing is adjusted to compensate.

Now that i think about it, if you were very bored you could use those independently actuated valves to control valve timing to effectively reduce compression by not fully evacuating the combustion chamber. Seems like a lot of work when you can simply adjust spark.

And now that I'm really thinking of it, i wonder if that oddball saab engine with variable compression would adjust it's compression based on knock?

back in the day you could get a "knock sensor" which was something you bolted to the engine, it would "hear" ping and ground out, blinking a little light on your dash. you could then use your cable-operated timing adjustment knob to advance/retard as necessary. Motorcycles used this too but mostly for kick starting without risking your leg.

Doing a little reading. It is still related to speed but not the way you meant with a timing chain connecting the crank to the camshaft
What Is A VVT-i Engine? (jdpower.com)

If you dig into it you’ll find that the camshaft has two profiles: low speed and high speed. At a set rpm the camshaft profile is changed. “The vtech kicked in”.
But knock doesn’t come into play here.

As you look at more modern valve train management systems it gets even more complicated. I’m going to guess we will see mainstream cam-less engines as mpg requirements continue to rise. Maybe those will do something when knocking occurs.

 

[mpeugeot]

In the context of this discussion, knock and octane, I don't believe any engine adjusts valve timing or lift to reduce knock. I could be wrong, but most modern engines adjust valve timing and lift based on rpm through the use of variable cam lobes, or in cutting edge tech, independent actuators.

valves are timed - yes.
octane impacts valve timing - no.
octane impacts pre-det/knock. knock sensors communicate this to engine management, and ignition timing is adjusted to compensate.

Now that i think about it, if you were very bored you could use those independently actuated valves to control valve timing to effectively reduce compression by not fully evacuating the combustion chamber. Seems like a lot of work when you can simply adjust spark.

And now that I'm really thinking of it, i wonder if that oddball saab engine with variable compression would adjust it's compression based on knock?

back in the day you could get a "knock sensor" which was something you bolted to the engine, it would "hear" ping and ground out, blinking a little light on your dash. you could then use your cable-operated timing adjustment knob to advance/retard as necessary. Motorcycles used this too but mostly for kick starting without risking your leg.

If you dig into it you’ll find that the camshaft has two profiles: low speed and high speed. At a set rpm the camshaft profile is changed. “The vtech kicked in”.
But knock doesn’t come into play here.

As you look at more modern valve train management systems it gets even more complicated. I’m going to guess we will see mainstream cam-less engines as mpg requirements continue to rise. Maybe those will do something when knocking occurs.

It's possible that Ford's engine management strategy could decrease/increase valve overlap depending on the detection or lack of detection of events by the knock sensor. Without being able to generate those events and attempting to record the strategies that the engine management implements to decrease knock events we don't know for sure.

 

[5GENIDN]

In the context of this discussion, knock and octane, I don't believe any engine adjusts valve timing or lift to reduce knock. I could be wrong, but most modern engines adjust valve timing and lift based on rpm through the use of variable cam lobes, or in cutting edge tech, independent actuators.

valves are timed - yes.
octane impacts valve timing - no.
octane impacts pre-det/knock. knock sensors communicate this to engine management, and ignition timing is adjusted to compensate.

Now that i think about it, if you were very bored you could use those independently actuated valves to control valve timing to effectively reduce compression by not fully evacuating the combustion chamber. Seems like a lot of work when you can simply adjust spark.

And now that I'm really thinking of it, i wonder if that oddball saab engine with variable compression would adjust it's compression based on knock?

back in the day you could get a "knock sensor" which was something you bolted to the engine, it would "hear" ping and ground out, blinking a little light on your dash. you could then use your cable-operated timing adjustment knob to advance/retard as necessary. Motorcycles used this too but mostly for kick starting without risking your leg.


If you dig into it you’ll find that the camshaft has two profiles: low speed and high speed. At a set rpm the camshaft profile is changed. “The vtech kicked in”.
But knock doesn’t come into play here.

As you look at more modern valve train management systems it gets even more complicated. I’m going to guess we will see mainstream cam-less engines as mpg requirements continue to rise. Maybe those will do something when knocking occurs.

Well I owe you an apology it appears. My attempt at a simple explanation based on the audience appears to have missed the mark with you since I have given the appearance a lack of comprehensive knowledge of modern engine management.

And as I would say to one of my three adult sons... You win... no matter what I say you will look past it and find fault. Wow you are so smart. I tried to find common ground where we could communicate.... But obviously I don't know enough.

 

[jzweedyk]

Well I owe you an apology it appears. My attempt at a simple explanation based on the audience appears to have missed the mark with you since I have given the appearance a lack of comprehensive knowledge of modern engine management.

And as I would say to one of my three adult sons... You win... no matter what I say you will look past it and find fault. Wow you are so smart. I tried to find common ground where we could communicate.... But obviously I don't know enough.

He is from California, and he doesn't have a Bronco, or he doesn't know how to update his info. Internet smarty.

 

[hozer]

The question one must ask themselves is why.

Yeah 93 Octane is better, but for what? If you've got an extra 50c/g to throw on happiness more power to you. I can say that saving 50c/g in an hour of stop and go traffic brings me more joy than the 12 seconds in a day i get to floor it to the next set of lights.

Your engine isnt going to last longer... Do y'all really have enough free time and open road where expensive gas actually gives you any extra joy? If so I need to reevaluate what Im doing with myt life and time lol

 

[Rydfree]

I run the cheapest gas I can find in my bronco the only reason i would run 91-93 would be if I were going to let the gas set in the tank for a long period of time. Iook at the owners manual and you can use 87 all the time.

The owners manual also says to put how many Qts of oil into the Bronco ?

 

[5GENIDN]

He is from California, and he doesn't have a Bronco, or he doesn't know how to update his info. Internet smarty.

What is frustrating is that he wants to prove how smart he is and to be honest he is fairly knowledgeable but there are others on here that I would turn to long before this guy.

I am not the smartest guy but I did spend 8 years wrenching on 16 to 20 cylinder hybrid diesel electrics where every cylinder had it's own cam.... After having spent several years working for an independent Auto shop where my boss had the first "Nitrous street car" on the cover of hot rod magazine. I then went on to earn four separate degrees although those were in land planning, structural design and Geographical Information Systems, after transferring from mechanical engineering. I have a clue or two. Again, there are people on here that know much more about this subject than I do. If this guy was to take the time and actually read some of the posts he might learn a few things rather than trying to prove how smart he is.

 

[7sKnuckledragger]

91 Is almost 7 bucks a gallon.... 87 is about .50-.70 cents cheaper per gallon here in SoCal, I ran 91 for the first 2k miles and recently switched to 87. After 600 miles, I have not noticed a difference in performance in my 2.7. I'm at 1700 feet and mild weather FWIW. I've ran 91 in all my cars since forever but now I'm just trying to save a couple nickels where I can.

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