Good reason to run a 6.2 on premium fuel

[Snowbound]

Wouldn't mind seeing documentation on that. All of my information states that the L92s are 10.5:1.

Yeah, your documentation is correct. I just said 10:1 but technically it’s 10.5:1. Splitting hairs.
I also said you can’t tune for 87 octane but I guess technically that’s false too. You can try to pull timing and could in essence run 87, but at a ratio above 10:1 it’s best to just use premium. That $0.60 national average premium increase is not worth the lack of power, higher emissions and lower fuel mileage IMHO.

 

[Stbentoak]

I used to have a vehicle that would throw a CEL on 87, fill it back up on 93 ...light goes out. While you CAN use it, it isn't desirable or good for the engine. Buyers know this before purchasing, why cheap out afterwards...?

 

[donjetman]

The first yr we owned our 07 Denali we ran 87 octane and got a DIC knock sensor warning once. Then we ran 89 octane for a while, then 91+ for a while. Long trip gas mileage was:
15.5 on 87
16.5 on 89
17.5 on 91+
Then Swathdiver made a post #30: https://www.tahoeyukonforum.com/threads/best-octane-fuel-for-fuel-eceonomy-5-3l-only.120104/page-3

about running a mix of E85 and unleaded. So for 6 mths we ran a 25% of E85 and 87. All went well. But its not practical for us because the closest E85 is 20 miles away and its not convenient on our long hwy trips. Currently I'm running 91+, but as fuel prices rise I'll probably switch back to 87 or 89.

 

[wsteele]

The first yr we owned our 07 Denali we ran 87 octane and got a DIC knock sensor warning once. Then we ran 89 octane for a while, then 91+ for a while. Long trip gas mileage was:
15.5 on 87
16.5 on 89
17.5 on 91+
Then Swathdiver made a post #30: https://www.tahoeyukonforum.com/threads/best-octane-fuel-for-fuel-eceonomy-5-3l-only.120104/page-3

about running a mix of E85 and unleaded. So for 6 mths we ran a 25% of E85 and 87. All went well. But its not practical for us because the closest E85 is 20 miles away and its not convenient on our long hwy trips. Currently I'm running 91+, but as fuel prices rise I'll probably switch back to 87 or 89.
View attachment 345999

Looking at your results of MPG between grades and using the normal markup in these parts for 91 (pretty consistently 10% premium over 87, not counting Shell's propensity to jack that "nitro" stuff way up), it would seem using 91 is a no brainer.

I will be doing some comparisons of 87, 91 and E85 from the perspective of knock retard and knock sensor activity with the various grades in my 5.3L LMG engine (9:9 CR). I think I will also start keeping track of the MPG results as well. I already suspect my results will likely mirror yours with the 6.2L Denali.

Like you, E85 is a pain to get here and the prices are not commensurate with the shortage of BTU's, so I will likely only buy it for my tests.

 

[a4edwin]

I’ve been jumping back and forth between 89 and 91

 

[a4edwin]

The first yr we owned our 07 Denali we ran 87 octane and got a DIC knock sensor warning once. Then we ran 89 octane for a while, then 91+ for a while. Long trip gas mileage was:
15.5 on 87
16.5 on 89
17.5 on 91+
Then Swathdiver made a post #30: https://www.tahoeyukonforum.com/threads/best-octane-fuel-for-fuel-eceonomy-5-3l-only.120104/page-3

about running a mix of E85 and unleaded. So for 6 mths we ran a 25% of E85 and 87. All went well. But its not practical for us because the closest E85 is 20 miles away and its not convenient on our long hwy trips. Currently I'm running 91+, but as fuel prices rise I'll probably switch back to

The first yr we owned our 07 Denali we ran 87 octane and got a DIC knock sensor warning once. Then we ran 89 octane for a while, then 91+ for a while. Long trip gas mileage was:
15.5 on 87
16.5 on 89
17.5 on 91+
Then Swathdiver made a post #30: https://www.tahoeyukonforum.com/threads/best-octane-fuel-for-fuel-eceonomy-5-3l-only.120104/page-3

about running a mix of E85 and unleaded. So for 6 mths we ran a 25% of E85 and 87. All went well. But its not practical for us because the closest E85 is 20 miles away and its not convenient on our long hwy trips. Currently I'm running 91+, but as fuel prices rise I'll probably switch back to 87 or 89.
View attachment 345999

I thought you couldn’t run e85 in 07 Denali.

 

[wsteele]

I thought you couldn’t run e85 in 07 Denali.

I think he was referring to @swathdiver's results, which I think is a rare 2009 6.2L Tahoe (I could be totally wrong about his rig).

 

[donjetman]

I think he was referring to @swathdiver's results, which I think is a rare 2009 6.2L Tahoe (I could be totally wrong about his rig).

07 Denali w/L92 & 170k miles now.
For six months everytime I filled up I pumped 4 gals of E85 in, then roughly 16 gals of 87 octane. No issues at all. All this driving was rural. Operating cost per mile is lower if you have a good E85 source nearby. We do not. Our source is 20 miles away

 

[donjetman]

I think he was referring to @swathdiver's results, which I think is a rare 2009 6.2L Tahoe (I could be totally wrong about his rig).

I also did this same experiment on my 07 Toyota FJ Cruiser w/214k miles. It has 10.5 to 1 compression engine too. I've owned this vehicle for 12 yrs and have always run 87 octane. Toyota "recommends" 91+ octane.

A while back its mpg dropped from 20+ mpg to 18-19. Running a 25% mixture of E85/87 restored its mpg to 20+. I've got it back on 87 octane these days.

 

[wsteele]

07 Denali w/L92 & 170k miles now.
For six months everytime I filled up I pumped 4 gals of E85 in, then roughly 16 gals of 87 octane. No issues at all. All this driving was rural. Operating cost per mile is lower if you have a good E85 source nearby. We no not. Our source is 20 miles away

Got it, sorry to introduce more confusion.

Yes E85 is a pain here as well. The guy who owns the one pump with it is a used car dealer whose lot is across the street (Fairly Reliable Bob). he prices the E85 at the same exact price as the lowest 87 E10 (typically Costco), which makes it totally uneconomic for anyone with a pencil and piece of paper and the slightest interest in what it costs then per mile to drive.

 

[donjetman]

E85 has two properties that I like:
#1) Hi octane
#2) it cleans things, like injectors, carbon deposits in the intake, combustion chambers, exhaust.
Once a yr or so I'll probably run a tank or two of the E85/87 mix just to keep things cleaned up.
There is another E85 station only 2 miles away but they charge as much or more than what they get for 87 octane.

 

[petethepug]

Seems like a good place to drop this … An e85 kit for around $995. that’s compatible for the non e85 engines in the 07 & 08 YXL, YXL Denali & Esky ESV. Cant tell if standard wheel base is included.

Auto Products - eFlexFuel Technology

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[a4edwin]

I thought flex fuel trucks had different injectors.

 

[donjetman]

I believe FlexFuel vehicles do have higher capacity injectors because there 17% less energy/BTUs in E85 compared to unleaded gasoline

 

[wsteele]

I thought flex fuel trucks had different injectors.

Here is a rundown on flexfuel. It doesn't answer the exact question for a given component as I believe many components are shared, once FF is introduced in volume. It is cheaper to just build them all to be compatible in a line that has a lot of FF offerings. I think higher volume injectors and fuel pumps are pretty universal.

A Brief Explanation of Flex Fuel | NewGMParts.com

NewGMParts.com defines flex fuel and what that means for your vehicle in terms of fuel, repair, and maintenance costs. Buy Parts for Your Flex Fuel Vehicle Online Today!

www.newgmparts.com

 

[swathdiver]

Seems like a good place to drop this … An e85 kit for around $995. that’s compatible for the non e85 engines in the 07 & 08 YXL, YXL Denali & Esky ESV. Cant tell if standard wheel base is included.

Auto Products - eFlexFuel Technology

Explore our family of eFlexFuel products for cars, SUVs and trucks.

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Non FlexFuel engines can easily run E15 and some to E20 or more without issue. When I typed on my year, only a Sierra was an option and then only a 4.3 V6, not even the old 4.8 or LY5 5.3 which were not FlexFuel as those engines must have the larger injectors to burn E85.

 

[Snowbound]

E85 is 104-105 octane and can tolerate a higher CR. It cools the intake charge better and therefore makes it more knock-resistant and it also makes the engine run cooler and to some degree, even safer. In most cases it's at least 5% more effícient than gasoline at the same lambda value (up to 25% more efficient on some cars optimized soley for E85). Since E85 has very good cleaning properties as well as leaving behind a by-product of water, it is cleaning the fuel system and it will keep the injectors nice and clean. The combustion chambers, valves, ports and the exhaust will also be cleaner, almost like the car had water injection. In most cases it will cost less $/mile to run on E85.

The down side of E85 is moisture and is a little harder to start in cold weather. It also requires about 42% more fuel to reach stoichiometric, or ideal air fuel ratio. So the stock non-E85 fuel injectors and pump will need to be replaced. You would need injector data segment swap in the tune and also add fueling to VE map and could also add more timing. Issue is for us in the Midwest, E85 isn’t so easily sourced and winter it’s almost useless. So unless you installed a fuel composition sensor and used a flex fuel ECM that would switch between the maps, it’s more of a pain than it’s worth.

The good thing is the O2 sensor doesn't care what fuel its running. It doesn't even know. It will make adjustments to run a 14.7:1 AFR, or Lambda 1. E85 is 9.765 stoich, or Lambda 1. So your O2 just looks for Lambda, not AFR.

 

[swathdiver]

This is my truck's average fuel economy burning E10 versus E85 since 2017 and the differences between the two calculated. As one can see, the difference is a lot less than claimed.

Been playing around with alcohol content and R+M octane rating calculators for some time now. I too read that E85 is claimed to be 103 octane, 113 octane, etc. Many different states and governing bodies have also tried to assign octane ratings to the lower ethanol content numbers and whenever I've made a calculator, the numbers never jived. Until recently! Sunoco markets E85R race gas which is a full 85% ethanol. Street legal never gets higher than 83%. Anyway, the important part is, the cans are marked 99 octane. So when I used that number and made a calculator, it jived much closer to what folks tried to assign to E20, E30, E40, etc.

So having said that, if you get a winter blend of 71% ethanol, the octane rating of that fuel is actually 96.8. If you get 51% for example, the octane rating would be 93.7. Of course if you mix some grade of ethanol with 87 or 93 you'll drag those numbers down. Figuring it out all is tough here because we never know what is coming out of those fuel pumps, even Racetrac has been off lately and our governing body is more interested in running for office than doing her job.

 

[wsteele]

Here is a clip I took this morning with a full tank of E85. The percentage is about 80% ethanol. My virtual sensor says about 59% this morning.

I didn't display all eight cylinders as I wanted to see the TP% and RPMs to compare to previous tests.

What I found out is the engine still hits the knock sensors when accelerating but far less than the 87 E10 I was testing in previous clips. In normal around town driving with normal acceleration I never picked up the knock sensors lighting up, only on sustained hard throttle situations, going up hill.

I will test E10 91 octane next.

 

[a4edwin]

I ran about three tank full of 89 a noticed a rattling sound as I cruised down the street under light acceleration. Filled up with 93 and the rattling went away