87 or 91 octane gas

[Miami-Dade]

If you are at 191k miles using 87 octane without any issues or knocking, then I'd say keep on using it.

@Nagloc68 I agree with this.

 

[Capybarbro]

If you want actual data on the topic AAA did a study on this a few years back using a '16 Escalade. The only car that experienced knock was the Audi A3.

Engineering Explained does a good breakdown and is worth 13 minutes of your time in my opinion.

 

[West 1]

I had a 2007 Escalade with the 6.2L and 6L80, it demanded Premium and the manual tells you to run premium, if you ran regular it did not like it. It was rated 403 HP I think. My current 2008 Yukon is a Denali, also with the 6.2L and 6L80. The Denali is rated at 380 HP, same engine but different tune GM manual says you can run it on 87 octane but it may run stronger on 91 octane. It runs just fine on 87 even when towing. MPG seems the same as the Escalade. I do not race them so power seems the same to me.
Never have had any knock issues detected.

It did heat up towing last weekend, trailer weighed 6500 pounds, towing in 100* heat going up long steep grade it started to get hot. Could there have been minor detonation helping it get hot??? Good question, I detected no pinging but my ears are not the best. No check engine lights at all. If I detect any knock from detonation I will upgrade to 91, till then it likes 87 just fine.

 

[swathdiver]

We haven't towed or anything else heavy - mostly hauling the four kids. Now its mine I mostly highway driving. Chicago suburbs area, Premium is about $1+ per gallon over 87. I fill up at Costco and save about 25-35c over local stations (used to be 50c). Costco doesn't have E85 at my location. I will check the price of E85 and maybe experiment a little. Thanks again.

Why buy one of the most luxurious and expensive and powerful vehicles on the planet and then fret over the choice of fuel?

You folks must drive it pretty easy because we routinely see broken pistons and piston rings after about 100K miles where the engine had been fed a steady diet of low octane fuel. You are the exception to the rule and I think that may be because of your locale.

I'm the opposite, I want maximum performance and range from my vehicles and run 93 even in my chainsaw and generators and lawn mowers.

 

[Marky Dissod]

Noticed in this video that, up the really steep grade, 8th gear was not useful. With superior axle gearing, trans might stay in 8th longer,
shift less often leading to longer life between rebuilds, and help engine last longer by making it work not quite as hard.

My current '08 Yukon is a Denali, also with L92 6.2L & 6L80. Denali's L92 is rated @ 380HP, same engine but different tune;
GM says you can run it on 87 octane but it may run stronger on 91 octane. It runs just fine on 87 even when towing. MpG seems the same as the Escalade.
I do not race them so power seems the same to me. Never have had any knock issues detected.

It did heat up towing last weekend, trailer weighed 6500lb, towing in 100F heat going up long steep grade it started to get hot.
Could there have been minor detonation helping it get hot? Good question, I detected no pinging but my ears are not the best. No check engine lights at all.
If I detect any knock from detonation I will upgrade to 91, till then it likes 87 just fine.

Any engine about to work/play hard deserves 91 in advance, even if the ecm/pcm canNOT advance timing to make more power / improve BSFC,
upper cylinder lubricants in 91 won't hurt and might help - and every GM V8 since the LS1 has two spark timing tables, Low & High Octane, so 91 will always help.

Best ears on the planet can only compete with knock sensors without an entire vehicle between the engine and those ears.
No ears will EVER detect knock / ping from the driver's seat before the knock sensors.
Mild knock/ping does not trigger any check engine lights, the knock sensors just do their job and retard (heh) the spark timing, however
it's important to note the pcm never truly learns to adjust timing based on knock sensor responses.
So if it only needs 2-4° of retard to avoid knock/ping, it'll retard 2-4°, stop knocking, then try for more timing til it needs 2-4° of retard again,
and you'd never hear it or notice the ecm say anything, all the way up Eisenhower. Forgot how much spark retard is required to trip a code, but it's more than 4°.

Long story short, even if an L92 does 'just fine' on 87, unless it's being driven 'daisy', especially when the engine is working or playing hard,
especially uphill in increasingly thin air, it'll do better on 91.

 

[West 1]

Knock sensors and computer controlled timing have made engines much more reliable. No doubt. Fuel Injection and O2 sensors have helped engines live far more than most people know. Fuel injection really took over in the mid 80's early 90's. It took a few years for the effect to hit the market. Carbureted engines were almost always needing an overhaul around 100,000 miles. The Fuel Injection engines suddenly started lasting twice that long because the fuel mix was so much better you had far less cylinder wear. They also switched to Moly Top rings at about the same time and the rings and fuel injection really helped engines last.

We provided Engine Bearings, Pistons, Rings, Gaskets and many other parts to the Production Engine Rebuilders, we were not the only provider but we were either #1 or #2 in almost all Production Engine shops. PER's as we called them. As the basic manufacturer we were tied to both OEM and Aftermarket sales. About 50% of our production went in new cars and 50% was sold in the aftermarket. Once the Fuel Injection cars started hitting the repair age our sales in the aftermarket dropped like a rock. Between 1999 and 2003 sales fell almost 50%. It happened so fast many Rebuilders went out of business because sales did not cover overhead.

There was one other factor that affected this, in this same time period cars started to all have Airbags. Cars that had very low miles on them were in small fender benders and the insurance company would total them due to the cost to replace airbags. These low mile cars all had good engines that were now for sale at wrecking yards and competing with the engine rebuilding market.

Sorry, that is a lot of history not pertinent to the above discussion but the point is, the OEM's now have computer controlled engines with Fuel injection and knock sensors and are far more reliable and durable (when they are built correctly) than any engines from our past.

I have seen hundreds of engines with piston damage from detonation, lean burn, overheat etc. I have not seen GM 4.8, 5.3, 6.0 or 6.2 engines with broken ring lands or damaged pistons from running 87 octane. I have seen many that were damaged by the owner switching to a tune for better performance. These owners may have ran with a tune on 87? That I do not know, but I have seen the damages done so my experience has me sticking with the OEM tune.

At one point we had 26 Dyno's running 24/7 doing Piston, Gasket, Rings and Bearings development work.
Some of these tests are far harder than any engine will ever see.

To sell a piston to Ford you had to prove it could run at Wide Open Throttle on the Dyno at max HP RPM for 300 Hours straight! That is 12.5 Days at wide open throttle. If Max HP was at 5800 RPM that engine would scream at 5600 RPM against the dyno for 12.5 days! A little extreme but madatory to pass that test to sell Ford a piston. On the upside if you got the contract you might sell 80,000 pistons a month to this customer.
Most testing was brutal but necessary to find flaws and expose them. Once a piston passed all the standard OEM tests we would subject the same piston to Nitros tests just to see where weak spots were. The final test if Nitros did not kill the piston was to advance timing till detonation finally killed the piston, again just to analyze the failure point.

Since we manufactured many parts we were able to test the Gaskets - Fel Pro and the Engine bearings - Federal Mogul, Spark Plugs- Champion, Pistons and Rings - Sealed Power.

Detonation testing was super interesting because they had pressure sensors in each cylinder to watch the pressure change as detonation was introduced. Factory stock the engine would make 600 PSI at wide open throttle cylinder pressure. When you introduced Detonation with excess timing the cylinder pressures would jump as high as 3600 PSI. That pressure is what breaks TOP Ring Lands in pistons and fractures the Top Piston Ring. Detonation is very dangerous.
The most dangerous detonation is when you get two flame fronts in the cylinder. Advance timing or lean burn conditons make any sharp edge in the chamber start to glow red from heat. That point glowing red will act like a spark plug and set off your fuel charge. This is classic detonation, the fuel charge is ignited as the piston is pushing up but well before the spark plug was supposed to ignite it. The piston is being pused by 7 other cylinders so it has a lot of power pushing it up, now it is pushing against the early explosion from the hot spot. As the piston continues up the spark plug finally ignites setting off more fuel, so you can have two flame fronts burning and under pressure from the piston still rising in the cylinder.

These two flame fronts basically cause a swirl that acts like a blow torch. I have seen pistons with a smooth hole melted right through the piston head. I have seen cylinder blocks with a hole torched right between two cylinder's. It happens. I have seen these cases many times.

With factory tunes you usually only see this type issue when you have a lean burn condition. Either a vacuum leak or a plugged injector. When you have 7 good running cylinders and one going lean it is hard to catch it before damage happens but your computer should pick up misfires or a change in the power that cylinder produces and try to save you before you have damage. In a perfect world.

When you have customers doing thousands of engines every month you get a lot of feedback and see a lot of issues. Most rebuilds are trouble free but not all.

Sorry to be so wordy, but I have seen many things in engines and engine development that most will never be exposed to.

 

[Capybarbro]

I'm the opposite, I want maximum performance and range from my vehicles and run 93 even in my chainsaw and generators and lawn mowers.

If I had money to literally throw down the drain, I would do that too. Unfortunately, I don’t. I think most people don’t either. But hey, maybe one day I will!

I’m not telling anyone what fuel to run in their vehicle, I just provided hard data instead of anecdotal octane comments.

 

[Marky Dissod]

I have seen many things in engines and engine development that most will never be exposed to.

What you've seen is of considerable value, no doubt.
Only thing I & and other considerably more experienced tuners have seen, is that the ecm can only DETECT misfires/knock, it canNOT predict.
Engine only has sensors that detect, from which a very quick response follows, but prediction would be more preventive.

This, the fact that every GM pcm/ecm since the LS1 has a High Octane spark timing table & a Low Octane table,
the extra upper cylinder lubricants in 91, and that GM bothered to cite 2 separate power ratings on 87 (380) & 91 (400),
strongly suggest that if the engine is working or playing hard, 91 is a prudent precaution.

If you're driving like a jacquesarse you can always let up and lighten the engine load far more easily than if you're towing over 3tons uphill into thin air.

One more thing:
it's a known fact among tuners that a vehicle that tows/hauls heavy canNOT use as much spark timing advance without knocking,
as a vehicle that is unladen. Learned it tuning a Fleetwood V4P (3.42) after tuning a Roadmaster wagon (2.56) up a very long very steep hill,
and that hill was much closer to sea level than the Eisenhower pull.

 

[Joseph Garcia]

There is a lot of conversation above about the 2007 L92 for the Yukon Denali being advertised at 380hp with 87 octane and the L92 Escalade being advertised at 405hp with 91 octane. Lots of opinions and discussion, and that is good.

In my conversations with Justin at BlackBear Performance, he stated that the 2 motors are identical, except for the tune. He also stated that this difference was a marketing tactic used by GM to promote the 2 similar, but different SUVs, to 2 different targeted buyers. The targeted Yukon Denali buyers were folks who wanted a luxury SUV as a 'stretch' purchase, but did not want to pay for 91 octane gas for the SUV's life cycle. The targeted Escalade buyers were folks who wanted a luxury SUV as the 'appropriate' purchase, and for whom paying for 91 octane gas was not an issue. Further, the additional 25hp advertised for the Escalade was part of the incentive/justification to pay the additional ~$15,000 in purchase price for the Escalade over the Yukon Denali.

One final note, regardless of what GM advertised in marketing literature for the 2007 L92 Yukon Denali (87 octane), and what was written in the owner's manual (87 octane is OK, if no knocking occurs), the sticker on the inside of the fuel door states that the recommended fuel is 91 octane.

 

[Marky Dissod]

the Escalade's additional 25hp was part of the incentive/justification to pay the additional ~$15,000 in purchase price for the Escalade over the Yukon Denali.

$15,000
÷
25 horses
=
$600 per peak horsepower
(over 5000RpM)​

...

 

[swathdiver]

If I had money to literally throw down the drain, I would do that too. Unfortunately, I don’t. I think most people don’t either. But hey, maybe one day I will!

I’m not telling anyone what fuel to run in their vehicle, I just provided hard data instead of anecdotal octane comments.

Well, see there's the difference. You see high octane fuel as a waste, I see it as a necessity. My engines run cleaner, cooler, make more power, are more fuel efficient and will likely last longer than if they were fed a steady diet of low octane fuel. I proved this nearly 40 years ago. The only engine type that has proved me wrong are the newer direct injected gasoline engines. To each, his own.

 

[Joseph Garcia]

$15,000
÷
25 horses
=
$600 per peak horsepower
(over 5000RpM)​

...

The math of the situation was never a thought for Escalade buyers.

 

[Capybarbro]

Well, see there's the difference. You see high octane fuel as a waste, I see it as a necessity. My engines run cleaner, cooler, make more power, are more fuel efficient and will likely last longer than if they were fed a steady diet of low octane fuel. I proved this nearly 40 years ago. The only engine type that has proved me wrong are the newer direct injected gasoline engines. To each, his own.

I’d like to see data from this decade that proves engines run “cleaner and cooler” on higher octane fuel. They also only started certifying top tier fuel in 2004. So your 40 year old anecdotal evidence may need to be revised. But if you want to live on 80’s information you can do that.

I’d also argue that since you care enough about your engines to run 91 octane you also maintain them pretty well. I’d wonder if all your engines would still be running just fine if the only variable you changed was octane?

I think we can both agree that running top tier certified fuel is the way to go though, even if we can’t agree on octane.

Also, yeah GM recommends premium. It doesn’t require premium. I have a Toyota with a 2ZZ-GE engine that has a 13.5 to 1 compression ratio. That REQUIRES premium.

 

[intheburbs]

My answer is short and sweet - I don't trust the knock sensors to be able to react quickly enough to prevent engine damage.

My Denali is not a daily driver, but when I take it out, it's going to 6000 RPM at WOT at LEAST once. I've owned it for 11 years and I've never put anything in the tank besides premium. One of these days, when I remember to let the tank go below 1/4, I'll put in E85 and see if that adds any fun.

 

[Scarey]

Octane is about detonation, detonation is an explosion in your cylinder. If you hear it knocking, it’s exploding. Explosion means shorter engine life. Just because you don’t hear it knocking, doesn’t mean it’s not exploding. You want a gradual burn in your cylinder to create the push, not an explosion. If the manufacturer says they recommend, I’m going to heed their warning. Period.

 

[homesick]

Octane is about detonation, detonation is an explosion in your cylinder. If you hear it knocking, it’s exploding. Explosion means shorter engine life. Just because you don’t hear it knocking, doesn’t mean it’s not exploding. You want a gradual burn in your cylinder to create the push, not an explosion. If the manufacturer says they recommend, I’m going to heed their warning. Period.

To be more accurate, detonation is an explosion AT THE WRONG TIME; hence the need for correct timing.

joe

 

[Scarey]

To be more accurate, detonation is an explosion AT THE WRONG TIME; hence the need for correct timing.

joe

You never want an explosion, you want a controlled burn at the correct time, timing. Octane is all about controlling the burn.

 

[Marky Dissod]

I don't trust the knock sensors to be able to react quickly enough to prevent engine damage.

No one should. Knock sensors REACT to knock, they canNOT anticipate or prevent knock, EVER.

 

[homesick]

You never want an explosion, you want a controlled burn at the correct time, timing. Octane is all about controlling the burn.

Set off by the explosion of the fuel being set off by the spark plug.

joe

 

[LSCALADE]

@LSCALADE, asking out of genuine curiosity.
Ever had the chance to compare the High & Low octane Spark Timing tables of an '07 L92 to an L94?
'cause it's not like GM couldn't write 87 octane tables for an L92 if they wanted to -
it's exactly what they did for the L76 & L77, which are 10.4:1, yet only require 87 octane.

Chevy L76 Car Engine Specs · Help Center

Chevy L77 Engine Specs · Help Center

Mild correction: L92/L9H/L94 are 10.5:1

https://help.summitracing.com/knowledgebase/article/HE-04847/en-us

Again, note that in '07, L92s were cited @ 380 horse on 87 octane by GM, not by a troll.

At sea level, 1/3rd of E85 (even if it's E51!) to 2/3rds of 87 octane petrol yields at least 91 octane.
At very high altitudes 1/2 of E85 (again, even if it's E51) to 1/2 of 85 octane petrol yields at least 91.

07-09 L92 were not flex fuel and I think had return fuel lines and small fuel injectors and ran around 55-60psi pump pressures.

The 09-14 L94 was a factory flex fuel with returnless fuel system runs around 45psi and has a virtual sensor that estimates the E content based on fuel trims. I am quite certain that the high octane spark tables will be different. I have a 07 and a 2011 and have been looking for ways to convert the 07 on Flex but its rather complicated process and I dont think its worth the effort. A donor 2009-up could provide the injectors and fuel components but I just dont have the time to mess with it.

Now All 2015-up L83 5.3L were flex fuel until around 2017 when the government subsidy expired and they took the sensors away and locked in the AFR to 14.67. I was able to undo that with a flex sensor install and copying over any tables from a 2015 that differed from what was in my 2020 and it works remarkably well. Hardware was around 80$ and programming was another 200 for the credits.