2017 Escalade/Denali L86 "requires" 93 octane - your experience?

[MobileHomie]

Why you sad Marky?
From your posts, I consider you quite knowledgeable, is there something incorrect in my statement?

 

[Marky Dissod]

What you said made me kinda sad - not the same as 'you make me sad'. We cool ...

This used to be true for engines with only one octane spark table in the ecm / pcm (OBD1 L31).
(As for your bro's Wrangler, I've never seen its ecm / pcm files, but if he hasn't timed it from 0MpH-'something',
or tracked the MpGs, then there's no objective way to know if his 'thinking it runs better' is correct, or not.)

Today - actually, since '99, likely earlier - our pcms / ecms have 2 separate spark tables,
one for Lo octane (87), one for Hi (91).
The Lo Octane (87) spark table for the Gen4 6.2L engines seems to have been written for a very lightweight car with very low aero drage (a 'vette).
As a result, using 87 in an L92 / L9H / L94 is not a great idea at best (unless the engine is NOT in an SUV / pickup).
Using 87 and driving like an @r$e has been known to break these engines.
GM did not write those Low octane tables well enough to save those 6.2L V8s from idiots.

Since I've not yet seen the spark tables for any Gen5 V8s yet, I can't be sure either way whether (or not) GM wrote the L86 Low Octane spark tables so that the 6.2L DI could safely tolerate 87 octane regardless of how it's driven.

My take is:
if you use 87 in a GM 6.2L V8, I hope it's because the gas pump you just used had no 91 available,
and that you find 91 at the next available gas pump.
Til then, working (or playing) hard with a 6.2L using 87 is a bad idea at best, even if driven gently -
but if driven GENTLY, your odds of everything being just fine are not nearly as bad as if you leadfoot it on 87.
For best results - durability, longevity, MpG, throttle response / power - 91 is safer and superior.

It is POSSIBLE to tune an L92 / L9H / L94 (DETUNE may be a better word) to run SAFELY using 87, but this can only come at the expense of losing power / torque / MpG etc - and you'd need to find a tuner willing to retard the Low octane table, at a minimum. BlackBear likely will NOT, for example.

I do not know if an L86 (or L87) can be safely DEtuned to work / play hard with 87?
Injection timing is every bit as important as spark timing with Direct Injection engines.
I do know the 5.3L V8s work better using 91 vs 87 though. Depending on the price of 91, it MIGHT be worth it?

 

[RobH]

FWIW, this is a quote from the 2017 Escalade Owners Manual,

"Do not use any fuel labeled E85 or FlexFuel. Do not use gasoline with ethanol levels greater than 15% by volume.

Premium unleaded gasoline...with a posted octane rating of 93 is highly recommended for best performance and fuel economy. Unleaded gasoline with an octane rated as low as 87 can be used. Using unleaded gasoline rated below 93 octane, however, will lead to reduced acceleration and fuel economy. If knocking occurs, use a gasoline rated at 93 octane as soon as possible, otherwise, the engine could be damaged. If heavy knocking is heard when using gasoline with a 93 octane rating, the engine needs service."

Wikipedia says my L83 has an 11.0 to 1 compression ratio and the L86 has an 11.5 to 1 compression ratio. Wikipedia says the 2020+ regular gas 6.6 liter L8T engine for heavy duty applications has a 10.8 to 1 compression ratio, a little less than my L83. The L8T does not use AFM.

The factory 6L80 is not the robust transmission I thought it was, perhaps due only to the cheap factory torque converter combined with the AFM. With the Max Trailering Package and a tow rating of 8,600 pounds, my 3,300 pound travel trailer should not be a challenge.

My 5,400 pound Tahoe does get the same gas mileage on Regular as my 2,400 pound 1964 Corvair got on the factory specified 91 octane Premium. Unfortunately, GM has given us AFM and stamped steel torque converters with thin linings which will probably outlast most of the original purchasers but may bite those of us who run their vehicles longer or ask more of them.

With the 6L80 and slightly fuel saving AFM, my Tahoe has not been as robust as I expected. So I have a factory reman transmission and am looking to modify the engine to ditch the AFM. Oh well.

 

[Marky Dissod]

Wikipedia says the 2020+ regular gas 6.6L L8T engine for heavy duty applications has a 10.8 to 1 scr, little less than the L83. The L8T does not use AFM.

The L8T does NOT use Engine Half @$$ / Cylinder Confusion, or Engine Doze-Off.

On top of that, look at what the L8T DOES have, that CAFE-MpG-hamstrung GM V8s don't have:
Iron block - Longer stroke AND longer rod ratio - More displacement - Forged conn-rods - Forged crankshaft with additional central counterweights

To quote Wikipedia:
"... the L8T was designed specifically to assuage the heavy-duty truck market's concerns."
I think the other GM V8s were NOT designed to assuage any of the light-duty truck market's concerns,
because CAFE's concerns over-rode ours.
In other words, GM chose not to prioritize programming the 6.2L V8s to utilize 87 WELL.
That's what all the caveats are for - to blame the end user for 'over-using' 87.

Same goes for the 6L80E.
At least one of the torque converters used by the 6L90E is the same one used by the 6L80E,
yet the 6L90E manages to last tend of thousands of miles longer despite working much harder.
Turns out at least one of the differences (AGAIN) is in the programming of the 6L80E vs the 6L90E.

GM's engineers can do quite a bit. When they choose NOT to do something, I blame GM.

Long story short:
don't stop at disabling Engine Half @$$, have the 6L80E tuned as well to improve the TCC function.