Fuel grade

[JLMBT]

The 2022 and newer Yukon Denali, recommends 91 octane. Has anyone tested lower octane, and how that may or may not have affected the way the vehicle performs? Just wondering if you use 88 or 87, how will that affect the engine? Some folks have different ideas on this...I wanted to see what your thoughts were on this type of performance question...thanks for anyone that helps in your response.

 

[Doubeleive]

The 2022 and newer Yukon Denali, recommends 91 octane. Has anyone tested lower octane, and how that may or may not have affected the way the vehicle performs? Just wondering if you use 88 or 87, how will that affect the engine? Some folks have different ideas on this...I wanted to see what your thoughts were on this type of performance question...thanks for anyone that helps in your response.

it's a recommendation only, if it was any different it would say "required" that is the definition, no need to complicate it any more than that.
in furtherance it is simply a matter of lower octane "may" in some instance cause "engine knock" or pinging. driving it and consistently having engine knock could potentially cause internal engine damage over a extended period of time.
that is all period.

 

[Marky Dissod]

Recommended ... Not QUITE the same as required ...

Not nearly as well on 87 as it would on 91 octane, in terms of fuel economy, throttle response, performance measured against a stopwatch, and overall engine longevity.
The harder you drive, the better your engine will operate, the further the engine will go, and the longer your engine will last, with 91 octane.
The lazier easier you drive, the more you can get away with 87 octane - even then, 91 octane is ALWAYS better.

In the case of 6.2L V8s, using 87 for anything other than minimally demanding driving - one driver, no riders, unladen, unburdened, unhurried - may result in drivability symptoms that would not normally occur using 91 octane.

Whether or not you suffer symptoms using 87 that can be avoided with 91 depends as much on how it's being driven, as how well it's been maintained.

Just 'cause you can, doesn't mean you ever should.
I would NEVER tow / haul / drive 'hard' without using 91 octane in any 6.2L.

(My educated guess is that using 87 octane 'costs' anywhere 15 - 25 ft-lb of torque, regardless of RpM.)

 

[Joseph Garcia]

^^^x2^^^ Lots of opinions on this, but for me, I stick with the recommendations or better. It would be a shame to lose that wonderful motor. Also, if you choose to go with a lower octane gasoline, make sure that you use a top tier gasoline.

 

[Marky Dissod]

I don't consider my previous post an opinion.
That previous sentence is an opinion, however. Here's another one:
Using 87 octane when it says '91 octane recommended', in the long run, costs more than it appears to save.

 

[swathdiver]

The 2022 and newer Yukon Denali, recommends 91 octane. Has anyone tested lower octane, and how that may or may not have affected the way the vehicle performs? Just wondering if you use 88 or 87, how will that affect the engine? Some folks have different ideas on this...I wanted to see what your thoughts were on this type of performance question...thanks for anyone that helps in your response.

Using low octane fuel in a high performance, high compression engine results in constant knock and ignition retard which over time results in broken pistons and piston rings and of course, crummy performance. Generally speaking this knocking and pinging cannot always be heard because the trucks are so well insulated but can be seen with a scan tool. If it's good enough, it will even tell you which cylinders and how much.

 

[B-train]

I'm of a similar opinion, but my 2017 6.2L can run on 87 just fine. I'm not sure what's changed over the years. I think mine says 91 recommended as well. I've run 90K since I bought it on mostly 87 and it always runs fine. I have had a few instances where I've heard pinging, but it's seldom.

Also to note, these motors like ethanol fuel too. I've tried various blends of E85 and 87 to get a higher octane rating, as well as the cleaning properties of E85. Direct injection motors are more prone to carbon buildup, so that should help keep things cleaner. Mileage suffers a little depending on driving habors but it runs great.

 

[Stbentoak]

Recommended also means that if you chose not to follow the "recommendations" then GM does not have to extend you warranty if the problem you have can be traced to not following "recommendations."
IE: Using another weight oil than recommended, or putting "universal" coolant in your cooling system...

One of my wife's older vehicles would throw a CEL when you put 87 fuel in. Cleared up as soon as you put premium back in...

 

[Marky Dissod]

Using 87 octane fuel in a high performance, high compression engine results in constant knock and ignition retard ...

'constant' might be a lil bit of a stretch.
...
Any aftermarket tuner worth their weight in salt can write low octane tables for 6.2L V8s that will NEVER ping / knock ...
... so why did GM write low octane tables for 6.2L V8s that ping / knock unless you drive Miss Daisy?
I'd prefer 385 ft-lb & 375 horses knock-free, over 395 ft-lb & 385 horses that knock unless tailwind-driven downhill.

That said, consider this solution:
Add some E85.
If 2/3 of fuel in the tank is 87 octane gasoline, and 1/3 is E85, that tank of fuel is 91 octane.

 

[swathdiver]

'constant' might be a lil bit of a stretch.

Measure it with a scan tool and let me know.

 

[JLMBT]

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]

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]

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]

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]

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]

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]

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]

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]

“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]

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.