Premium vs regular gas

Elkman

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E15 is not gasoline so much as a subsidizing of Archer Daniels Midland profits. Figure a 25-30% reduction in fuel economy.

I am surprised that Octane Rating which has been around for nearly a century is not understood by 99% of the people buying gasoline at the pump. Octane is a measure of resistance to pre-ignition and nothing more.

The higher the compression ratio of the engine the higher the octane rated fuel that is needed to provide maximum power without pre-ignition which will damage the engine. If an engine is designed to use 93 octane rated gasoline is instead fed 87 octane rated gasoline, vehicles made in the last 30 years with their electronic ignitiion will simply retard the spark and no problem. A 10% reduction in miles per gallon but no damage to the engine.

Now if the engine is designed to use 87 octane rated gasoline and someone pumps 93 octane rated gasoline into the fuel tank then that will help the profits of the gas station but do absolutely nothing for the performance of the engine or prolong its life.

Higher octane rated gasoline has the same btu's available to power the engine as regular gas at the pumps. It is only when ethanol is added to the mix that the available btu's from a gallon of fuel drops.

Plenty of people ready to help the gullible spend more money on their vehicles. A friend of my wife was conned by the tire store where they convinced her to put "nitrogen" in her new tires at an additional cost. They failed to mention and the women did not know is that air is 80% nitrogen already and no measurable difference between 100% nitrogen and 80% nitrogen mix in tire performance or life. The devil is in the details but one has to take the time to think in a critical manner which seldom happens.
 

Atcer2018

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E15 is not gasoline so much as a subsidizing of Archer Daniels Midland profits. Figure a 25-30% reduction in fuel economy.
Do flex fuel vehicles see less of a reduction in fuel economy using E15? I have a flex fuel Pentastar and I’ve only used E15 three times. All three times were purchased on the Pennsylvania Turnpike at the start of a 400 mile all highway trip from my sisters home back to southeastern VA. I saw maybe a mile decrease per gallon via the computer readout. It’s not sold where I live so I have no other experience with it other than 60 mph with cruise control on most of the time.
 

HEMIMANN

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Superb (factual) rant, @Elkman , thank you.

So many people who don't know what they're talking about getting online and rambling to get attention, instead of just asking and learning. Sad.
 

Mister Luck

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I have seen fuel prices (locally) rise from $3.50 a gallon to almost $6.70 a gallon that is for premium rated 91 octane with 10% ethanol top tier gasoline.



The same gas station has a dedicated pump for zero ethanol fuel that is rated at 93 octane that was consistently priced at $5.00 a gallon, and now sells for about $6.50 a gallon.



Anyone with engineering or simple physics experience can point out that alcohol burns cleaner with less carbon by the amount of soot or smoke produced with open flame.

Alcohol also burns hotter but produces less energy than petroleum based fuel.



The hotter you can burn a fuel the more energy you can use (extract) in the form of combustion producing motion of mechanical assemblies.



This isn’t a discussion on what type of fuel but what octane, so I will not go into diesel versus CNG or Hydrogen.



Combustion and mechanical motion produces friction and inevitable wear.

The less heat and radiation from friction and the combustion cycle , the less wear will be evident in the mechanical assemblies subjected to it.



From this reasoning and knowledge I logically purchase the zero ethanol 93 octane at a $1.50 increase than to purchase a less efficient 91 octane adulterated fuel that has increased in price by $3.50 a gallon.



My driving habits have been modified to accept the reality of our economic shortcomings and although I can achieve a higher rate of acceleration in a less stressful combustion environment, (in this scenario) in order to benefit from the increased efficiency, I still need to measure self control on the gas pedal.
 

Tray Burge

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It doesn't. I've gone to 89 as I've noticed enough of a fuel economy improvement vs 87 to offset the extra cost, but premium to 89 I notice no difference. As I understand it the engine management will adjust for 87 octane fuel, but will run at it's peak on 89 or better.
I always run 87, but can you actually feel any difference with the higher octane?
 

BWL

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I always run 87, but can you actually feel any difference with the higher octane?
I actually think I do, but the right foot dyno has a lot of margin for error. If it's setting back timing to adjust for 87 octane fuel it makes sense though. For me it's been mostly that my many trips in the past were closing in on 14l per 100 km with my best around 13.4 in ideal conditions and on 89 it's been 13 or just under consistently. Not much gain, but enough to offset the cost now at current prices. Figure if the price per mile is the same and I gain some range it's worth it. I ran 94 chevron for 1 trip and it was still in the same range I got on 89 in my early experimentation so it seems there is no benefit exceeding 89 in stock tune.
 

Docwagon1776

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I always run 87, but can you actually feel any difference with the higher octane?

If you're driving at reasonably legal speeds with light or no load, aren't in extreme heat, aren't flooring it off the line or passing with authority, probably not. If you're putting the motor under heavier loads, spiking combustion chamber temperatures, then you have a better chance of noticing the difference. Hence why you hear so many people who can't tell the difference. They could de-tune their truck by 20% and not notice a difference, either. The capabilities far exceed their needs. Which is awesome when you think about it, as this is how incredible modern trucks are compared to their counterparts of the 2000s and earlier.
 

HEMIMANN

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Since I've been running 87 octane (10% ethanol) during this gas price spike, I too have noticed it doesn't run as well. Sputters some at idle and light load. This compared to 89 octane (10% ethanol) I used to run normally.

I speculate the ignition timing algorithm biases a bit too much toward r*e*t*a*r*ded timing as it senses knock, resulting in some partial combustion when lean.
 

Mister Luck

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Even if the pump has a button for premium doesn’t necessarily mean that what’s going in your gas tank.

For me shift points are advanced and slightly less stressful with higher octane.
 
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