6.2L V8 - 2021 owners

[Chloe_21]

Have a 6.2 in our '21 Yukon XL Denali. 90-95% is in town driving.

17mpg HWY cruise set at 84
15mpg HWY cruise set at 94

Around town 12-14mpg

Our overall average is 13.4 mpg with 5,084 miles. First 3,500 miles though we were in auto mode but now run in 2wd mode and do get about 1-1.5 MPG better.

Also, premium gas is not required and we don't use it. Tried it for around 2,000 miles and mpg difference was around 5% at best on the HWY and no difference at all in town. The only reason you need a higher octane is to eliminate knocking.

The knocking usually indicates failed lifters. The manual even says to not drive it if a knocking occurs. I believe.

so your MPG didn’t change at all with unleaded? I know premium is for best performance. But I may just try unleaded. If I ever get the thing. Lol.

 

[Gibby13]

The knocking usually indicates failed lifters. The manual even says to not drive it if a knocking occurs. I believe.

so your MPG didn’t change at all with unleaded? I know premium is for best performance. But I may just try unleaded. If I ever get the thing. Lol.

Yeah manual says if using lower octane gas go up a level and if knocking still occurs with 93 to get it serviced.

In terms of performance, I would guestimate around 0.01% better until we can actually start tuning them. Would love to be able to run a supercharger. Hopefully soon...

For it's size, on 87 she still moves pretty quick.

I've always ran 87 in all my 6.2's all the back to our '11 Escalade and had no issues.

 

[Chloe_21]

Yeah manual says if using lower octane gas go up a level and if knocking still occurs with 93 to get it serviced.

In terms of performance, I would guestimate around 0.01% better until we can actually start tuning them. Would love to be able to run a supercharger. Hopefully soon...

For it's size, on 87 she still moves pretty quick.

I've always ran 87 in all my 6.2's all the back to our '11 Escalade and had no issues.

That’s good to hear! Thanks for your responses!

I’m thinking while gas prices are crazy right now, I’ll definitely be trying the unleaded.

 

[Jdsuburban]

Duplicate

 

[Jdsuburban]

93 octane is that the engine was setup to run on. It mostly in the valve timing and ignition timing. Both of which are variable on this beast. There is also Direct Injection which adds another timing variable.

Ignition timing has always been available since before the model T. Although it was manual.

Variable valve timing has been around since the eighties.

Direct injection on the gen V made the introduction of fuel a variable and practically eliminated the knock or ping from low octane.

What GM did was to boost the compression up to 11.5 from 9.7 in the 6.2 and up to 11 from 9.6 in the 5.3. This would not have ever been possible with 87 octane if it were not for the Direct injection.

So the question is, what exactly happens when you put 87 octane in an engine designed for 93? On older cars with fewer variables, the ecu simply enrichened the fuel mixture when the knock sensors detected a ping. Cars with VVT could detune the timing. My guess is that on the 6.2l, there are enough variables that the engine can adapt the valve, ignition and fuel timing so that the result is just lower HP. Without having to waste too much fuel. The only thing they can’t change is the compression ratio. (they can artificially with valve timing) and that seems to be the main difference between the 5.3l and 6.2l and hence the recommendation for higher octane.

Some trucks like the TRX are putting out 700hp with the help of a supercharger so those trucks “require 91 or 93 octane.” GM 6.2 only “recommends 93 octane.”

That’s my take on it. I run 93 because I want my 420 HP. Otherwise I would get a 5.3l.

I figure it will cost me 3,750 at most over the life of the engine. The 6.2l option costs more than that.

 

[Chloe_21]

93 octane is that the engine was setup to run on. It mostly in the valve timing and ignition timing. Both of which are variable on this beast. There is also Direct Injection which adds another timing variable.

Ignition timing has always been available since before the model T. Although it was manual.

Variable valve timing has been around since the eighties.

Direct injection on the gen V made the introduction of fuel a variable and practically eliminated the knock or ping from low octane.

What GM did was to boost the compression up to 11.5 from 9.7 in the 6.2 and up to 11 from 9.6 in the 5.3. This would not have ever been possible with 87 octane if it were not for the Direct injection.

So the question is, what exactly happens when you put 87 octane in an engine designed for 93? On older cars with fewer variables, the ecu simply enrichened the fuel mixture when the knock sensors detected a ping. Cars with VVT could detune the timing. My guess is that on the 6.2l, there are enough variables that the engine can adapt the valve, ignition and fuel timing so that the result is just lower HP. Without having to waste too much fuel. The only thing they can’t change is the compression ratio. (they can artificially with valve timing) and that seems to be the main difference between the 5.3l and 6.2l and hence the recommendation for higher octane.

Some trucks like the TRX are putting out 700hp with the help of a supercharger so those trucks “require 91 or 93 octane.” GM 6.2 only “recommends 93 octane.”

That’s my take on it. I run 93 because I want my 420 HP. Otherwise I would get a 5.3l.

I figure it will cost me 3,750 at most over the life of the engine. The 6.2l option costs more than that.

If the Denali had the option, I would’ve gone with the 5.3 engine, it was fast enough for me for around town; but I don’t like the lower models I like the Denali and I like the get up and go of the 6.2 for freeway.

 

[xycrazy]

I’m averaging about 20.8 with 90% hwy. I had a flat a week ago and had to drive at or below the speed limit for about 85 miles, mostly hwy and netted 23.7 MPG!

If you stay in DFM mode you can hyper-mile some serious mileage out of these big trucks. I was driving on backcountry roads for almost 2 hrs for work the other day and even though the roads were really hilly I averaged almost 22.5 MPG as I was at or below 65 MPH the whole time and most often in DFM mode.

How do you know that you’re in DFM mode??

Yes, that’s with the 6.2. DFM stands for Dynamic Fuel Management and allows our Yukons’ motors to operate on less than 8 cylinders and all the way down to 2 cylinders, I believe. Here’s an interesting write up:

https://gmauthority.com/blog/gm/gen...-management-cylinder-deactivation-technology/

If you’re light on the throttle then you’re able to keep out of the full “8-cylinder” mode and save fuel by running the engine on less capacity, so to speak. Others here with lots more engineering aptitude can chime in to correct anything I’ve stated in error or provide more clarity around the technology.

How do you know that you’re in DFM mode??

 

[Reddevil96]

Ive had a best of 19.5mpg on highway at 82-84mph and with a very light foot can get 13-14mpg around town with a 6.2 XL Denali 4x4, and will only run 91 or better. I run 39-40psi tire pressure, and have changed oil twice since new in 3k miles. Oil is cheap, 91 octane is reasonably cheap. Engine is not cheap. GM has the right to deny warranty if purposeful neglect if suspected, believe these new vehicles are quite capable of recording any and all data including fuel quality, max speeds, max loads, etc. for those of you that think you not hurting anything on 86 or 87 octane clearly have ZERO idea what happens when your engine is pinging/detonating. Yes the ECM can retard timing, but only to a certain amount.

 

[Geotrash]

93 octane is that the engine was setup to run on. It mostly in the valve timing and ignition timing. Both of which are variable on this beast. There is also Direct Injection which adds another timing variable.

Ignition timing has always been available since before the model T. Although it was manual.

Variable valve timing has been around since the eighties.

Direct injection on the gen V made the introduction of fuel a variable and practically eliminated the knock or ping from low octane.

What GM did was to boost the compression up to 11.5 from 9.7 in the 6.2 and up to 11 from 9.6 in the 5.3. This would not have ever been possible with 87 octane if it were not for the Direct injection.

So the question is, what exactly happens when you put 87 octane in an engine designed for 93? On older cars with fewer variables, the ecu simply enrichened the fuel mixture when the knock sensors detected a ping. Cars with VVT could detune the timing. My guess is that on the 6.2l, there are enough variables that the engine can adapt the valve, ignition and fuel timing so that the result is just lower HP. Without having to waste too much fuel. The only thing they can’t change is the compression ratio. (they can artificially with valve timing) and that seems to be the main difference between the 5.3l and 6.2l and hence the recommendation for higher octane.

Some trucks like the TRX are putting out 700hp with the help of a supercharger so those trucks “require 91 or 93 octane.” GM 6.2 only “recommends 93 octane.”

That’s my take on it. I run 93 because I want my 420 HP. Otherwise I would get a 5.3l.

I figure it will cost me 3,750 at most over the life of the engine. The 6.2l option costs more than that.

^^^ This. Excellent analysis and spot on. Owners of Gen IV 6.2L engines made the same arguments for running them on 87 octane that we see here, and now that we have the benefit of history, we can see the results. A primary failure mode is internal engine damage followed by catastrophic failure caused by running at high power on low octane fuel. The "I do cars" YouTube channel is run by a guy who's seen hundreds of them fail this way with his own eyes. We will see the same with the Gen V. Your engine, your choice, but it helps to have accurate information on which to make a decision. The assumption that the engine will be just fine on 87 octane fuel for the long term is demonstrably incorrect. It would be more accurate to say: "Using 87 octane fuel will damage my engine over time, but it will most likely last as long as I plan to keep it so I don't care. The next guy can deal with it."