Fuel grade

JLMBT · May 8, 2023

Wow!! All of you sound like experts..that's great to hear the different sides of octane levels for Yukon Denali..much appreciated on all of your thoughts..I think I know after hearing all of you, what direction I will go from my Yukon Denali. Thank you again.

Geotrash · May 10, 2023

Here's a guy who's analyzed more engine failures than any of us ever will. I deliberately linked to 16:20 as the starting point on this video. It's a teardown of a L94 (Gen IV) 6.2 after a catastrophic failure. And keep in mind that this engine has a lower compression ratio than the Gen V 6.2 does. So premium fuel matters even more in a Gen V. Note his comments that he sees a lot of broken pistons in the GM 6.2's from being run on low octane fuel.

Roll On · May 12, 2023

I’m no engineer that did any of the testing for GMC.
But it sounds like spitting hairs on the wording of recommended or requirement use of 91 octane.
I know someone who uses 87 octane in his Harley and it stinks to high heaven, I figure that it can’t be good for the catalytic converter, let alone anything else.
All your saving is a few dollars ($8.00) per tank, I would not recommend it.

Roll On · May 12, 2023

If you want to get into it, 100% pure gasoline has a higher BTU rating than the other grades, hence, better fuel economy.

Marky Dissod · May 12, 2023

Roll On said:
I’m no engineer that did any of the testing for GMC.
But it sounds like spitting hairs on the wording of recommended or requirement use of 91 octane.
...
All your saving is a few dollars ($8.00) per tank, I would not recommend it.

In NYC, regular is about $3.499 a gallon.
91 is 4.299 a gallon if you know where to find it - might not be worth the time to drive to the cheaper gas stations.
26 * $3.50 = $91
26 * $4.30 = $111.80

The possible MpG improvement from 87 to 91 is not worth the 'premium', at least not here.
But if it's a 6.2L, I'd use 87 ONLY if I drove like the toes in my right foot were broken while trying to hypermile.
I'd very strongly consider using some E85 if it were available to mix with the 87.

THarber · Jul 4, 2023

All of these engines can run on 87 but if you could see how much timing the ECM pulls out to do so you would be amazed. WHen you are pulling 25 degrees or more of timing to accomodate cheap fuel you are defeating what the engine is supposed to do in the first place. Fuel helps cool and lubricate the pistons and valves and that is set up by spark timing, too much or too little and you have issues. You might not hear spark knock but it is there and causing performance issues weather you thihnk so or not. Premium is the best choice and in the long run I think about the same cost as mpg will increase as well. I am not implying that you are going to do any damage if you get that cheap tank of fuel here and there. If forced to do so, I have done so in the winter because outside temps effect IAT's which help to reduce knock.

Marky Dissod · Jul 4, 2023

I agree with the sentiment, but not with some of the details.
Warning: nuances ahead.

The ECM is NOT pulling timing.
Since the early oughts, these ecms have a separate Low Octane Table and a High Octane Table.
The timing is determined by interpolating between both two tables.
If you run 87, the bias will tend toward the Low Octane Table.
If you run 91, the bias will tend toward the High Octane Table.
You can guess what happens if you run 89, or 93.

Just 'cause you don't hear spark knock or ping, doesn't mean you're experiencing it if you're running 87.
Only way to know if, or how much knock, is to actively scan realtime readings and look at the knock sensor counts.

If you run ethanol, there is an ethanol modifier table, applied proportionally based on readings from the Fuel Composition Sensor that analyzes the ethanol portion in the system at each startup.

Plenty of these engines are running very well on 87 Octane for upwards of 250,000 miles.

All that said:
OF COURSE these engines run better on 91 or 93 octane.
And, despite the MpG hit, they run better on E51-E83 too.

Marky Dissod · Jul 4, 2023

My advice - which some will not like, nevermind not take:
If you can afford to run 89, or 91, or 93, or E85, DO IT.

If you're afraid you have any issues, it pays in the long run to get acquainted with your engine's realtime data.

Onlyone · Jul 4, 2023

“I bought an expensive good running vehicle, can you de-tune it for me so it pings under hard loads. Also, it runs too good.”

-no one ever

THarber · Jul 5, 2023

Marky Dissod said:
I agree with the sentiment, but not with some of the details.
Warning: nuances ahead.

The ECM is NOT pulling timing.
Since the early oughts, these ecms have a separate Low Octane Table and a High Octane Table.
The timing is determined by interpolating between both two tables.
If you run 87, the bias will tend toward the Low Octane Table.
If you run 91, the bias will tend toward the High Octane Table.
You can guess what happens if you run 89, or 93.

Just 'cause you don't hear spark knock or ping, doesn't mean you're experiencing it if you're running 87.
Only way to know if, or how much knock, is to actively scan realtime readings and look at the knock sensor counts.

If you run ethanol, there is an ethanol modifier table, applied proportionally based on readings from the Fuel Composition Sensor that analyzes the ethanol portion in the system at each startup.

Plenty of these engines are running very well on 87 Octane for upwards of 250,000 miles.

All that said:
OF COURSE these engines run better on 91 or 93 octane.
And, despite the MpG hit, they run better on E51-E83 too.

How do you think it is accomodating the lower octane fuel in the table? It is pulling timing. Spark knock is very real and yes I have looked at this on HP Tuners. My truck will run as much as 42 degreees advanced with the right tune and premium fuel. Low octane will drop it into the teens if not full retard on a hot day. You can not run E85 in a non flex fuel vehicle and expect good perforamnce, yes it will run but it will do so at reduced performance. There is a huge difference in fuel flow from the pump to the injectors to fuel tables. A flex fuel vehicle has a sensor that you speak of that adjusts for that. A non flex fuel vehicle is not equiped to handle this. A gallon of corn has about 2/3rd the energy of regualr fuel. It has a higher ignition point and runs cooler but you have to tune for it. My sons twin turbo M4 will push almost 600hp on corn compared to 545hp on premium.

Fuel grade

JLMBT

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Geotrash

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Marky Dissod

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