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.