Ethanol Free Gasoline

[Geotrash]

Supreme gasolines will give you better mileage as long as you're tuned for it. That is because 93 octane has a greater energy density than 87 octane. However, cost wise I'm not sure you are ahead.

This is a common misunderstanding. All gasoline grades (setting ethanol blends aside for a moment) have the same energy density. The reason some engines generate more power and better mileage from premium fuel is because the higher octane allows for more spark advance without risk of pre-ignition. Here's an article from MIT that explains it more thoroughly:
https://engineering.mit.edu/engage/...e-between-premium-grade-and-regular-gasoline/

Cheers,
Dave

 

[gooffeyguy]

You could also fill her up with 22 gallons of 93 and 4 gallons of E85 and she would run even better still and this time you wouldn't have to worry about cracking pistons!

Why pay for premium, just put in 7 gallons of 87 and 19 gallons of E85

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[Larryjb]

This is a common misunderstanding. All gasoline grades (setting ethanol blends aside for a moment) have the same energy density. The reason some engines generate more power and better mileage from premium fuel is because the higher octane allows for more spark advance without risk of pre-ignition. Here's an article from MIT that explains it more thoroughly:
https://engineering.mit.edu/engage/...e-between-premium-grade-and-regular-gasoline/

Cheers,
Dave

Interesting. That has me investigating octane some more.

Peter Dunn does state that all grades of gasoline contain the same amount of chemical energy. I was hoping he'd explain or justify that statement a little more. I'm not sure how much I agree with his statement because I do believe that the amount of energy will vary a little between grades. But, as I have come to learn now, the amount of energy in a gallon of gasoline is actually irrelevant. Now, what he did explain fairly well was how octane is simply the resistance to knock.

So, after doing some other poking around, I came across this site which seems to explain things fairly well, probably better than I can:
http://www.rockettbrand.com/downloads/tech_bulletins/Tech-BTU Content of Gasoline.pdf

So, it seems I've been barking up the wrong tree. Instead of "energy density", we should be talking about "usable energy". In fact, energy density appears to be completely irrelevant. You may have a lot of energy in the fuel, but if it burns too slowly you won't get all the benefit of the fuel before the exhaust valves open and you're literally pumping wasted energy out the tail pipe. The site I referenced is geared towards racing with rpm's exceeding 7000. That's not my Tahoe. But, the site above got me thinking about the "usable energy" concept.

This may explain why some have reported worse fuel economy using 93 octane. From what I've heard on this site, the 5.3L may benefit from a mid-grade fuel

 

[Geotrash]

Interesting. That has me investigating octane some more.

<snip>

Instead of "energy density", we should be talking about "usable energy". In fact, energy density appears to be completely irrelevant. You may have a lot of energy in the fuel, but if it burns too slowly you won't get all the benefit of the fuel before the exhaust valves open and you're literally pumping wasted energy out the tail pipe.

YES. Exactly right. Way to assimilate info! I learn on these forums every day.

 

[JonnyTahoe]

100 Octane racing fuel 9.59 a gallon total rip off

100 octane unleaded should be about 5.39 a gallon it only cost a few pennies more a gallon to make..


if you have VVT it should max out the timing to 42 degrees BTDC


91 will do 36 degrees advancement or so (seen it occasionally at 42 degrees)..


I see 35.1-69% fuel efficiency increase with 91 Octane fuel over 87octane


active fuel management works better with 91oct or higher.


from 18.5mpg No matter how it's driven with 87Oct
trying super hard . No v4 mode or rapid loop v4-v8 etc..


25-31.3MPG with 91 oct (highway)

my last highway trip was 38.3mpg on the downhill side and 24.5mpg on the uphill side from LA to the High Desert averaged 31.3MPG




City is a hit or miss on the mileage since there is too much variable with traffic lights and train freight crossing and other traffic... it's typically around 20-22mpg. on two routes that i could take to get to certain areas i need to go.... the lowest ever was 12,14.5mpg when it snowed...

like lately I pretty much hit every single red light with in the last two days it came to 16mpg in the city still better then what many of you get...anyways..



I did Install the ECO tires they weigh 10 pounds less ea (to the drive wheels) Less wheel mass the engine has to spin(this matters a lot)


my goal is to get 40MPG I should make it to 40mpg with this 6.0L with a few eco mods so it will cost 400-800$ to go from somewhat gas guzzler to not a Prius , but Prius MPG.... plus it will lower my carbon foot print by 50%

note prius has a 1.5 L 4-cylinder..


it runs on ICE 100% of the time on the freeway so there is pretty much Zero cheating. on my end. with a Fully Optimized route that i take..


say if you go from 14mpg to 19mpg at $2.799 you will save 1$ for every gallon it would take about 800 gallons 1.5 years to get that money back at 12k miles a year saving 226 gallons of fuel in the first year..

These prices are a few years old.

 

[JonnyTahoe]

Why pay for premium, just put in 7 gallons of 87 and 19 gallons of E85 Lots of guys like to run all Premium why because they like the power and they can afford it.

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[gooffeyguy]

My last 3 fill ups have been premium, 93 octane, only because it's been priced at $2.35 or so. I usually run E85 because it's much cheaper then premium, but lately it's only been about 20-30 cents cheaper.

E85 is 105 octane and the ECU detects the alcohol content and runs more aggressive timing tables than the 93 octane tables.

When premium prices are high, like over $3 a gallon here, you can get the same 93 octane by mixing cheaper 87 with some E85.

GM recommends at least 91 octane with the 6.2l. Lower octane can be used, but the knock sensors will pull timing and the engine will have less power.

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[JonnyTahoe]

That's a great price for 93 octane. we don't have a lot of 93 around mainly 91. we got this 88 octane E-15 that's like 2.20 that's what I run in my 5.3. Runs great too. Fuel is cheap now and will only go up this summer so enjoy the savings.

 

[JonnyTahoe]

While driving through VA today (I live in NY) I came across a WaWa gas station that had "Ethanol Free Gasoline". I've never heard of this and didn't have time to google it then and there but did a quick search now and some sites say no changes and others say you can get increased mileage and better for older cars.

My '08 Yukon XL Denali says to use Premium but I've always used Regular, and I'm curious if anyone uses this gas and their thoughts on it?

Really, Wa Wa.

 

[swathdiver]

Why pay for premium, just put in 7 gallons of 87 and 19 gallons of E85

That mix delivers about 95 octane with about a 16% alcohol content. Oh, but yours delivers 99 octane and 45% alcohol content! Hmm. LOL

This may explain why some have reported worse fuel economy using 93 octane. From what I've heard on this site, the 5.3L may benefit from a mid-grade fuel

Been interested in maximizing fuel efficiency since earning my learner's permit. EVERY gasoline powered car benefited from running higher octane fuel, got more MPGs besides the other benefits and this was before the "Top-Tier" fuel standard. Didn't matter if it was an '80 Toyota Corolla, Dad's '85 Cadillac Brougham, Mom's '88 Cadillac Coupe De Ville, the Hyundais, Buicks and my old F-150 and all the other in between. The Montanas all greatly benefit from 93 over the others too. But lately, my wife says she's getting the same MPGs on 89 as 93 so there's that; come down to cents per mile in that instance.

Now more specifically to us here since we're all running these LS engines, my Gen IV motor runs smoother and gets better gas mileage running 93 versus anything less and also performs better with certain brands which for our locale is Chevron, then Mobil then Sunoco.

Now having said all that, our friend Gary here proved with his 2016 Direct Injection 5.3 motor that octane ratings didn't matter anymore. And recollecting, the same was true with my diesel engines back in the day as long as we were running the same kind.

Lately I've been experimenting with different mixes of fuel to maximize fuel economy even more. With an alcohol content of 25% which was made by mixing 18 gallons of E15 and 8 of E85, the truck got 19.1 MPG on the highway and was still climbing after two hours on the road. Also experienced better MPGs at higher speed 77+ than at 70 for a time. Still a work in progress.

We have a long trip coming up and would like to run these mixes but FlexFuel stations are not convenient for all of the trip, only parts so I'll probably keep her on gasoline. We shall see.