Fuel type

[travelinscout]

I got my brand new 2022 refreshed trailboss with the 6.2 motor and the salesman put 87 in it because he said the engineers at GM said 93 is recommended but not required for my motor. I noticed it idling a little rough at stop lights and such. Next tank I filled up with 93 and it smoothed out. 93 from here on. It's worth the extra what? 6 or 7 bucks a tank maybe? Whoopdie do. I'd probably still out 93 in if I got the 5.3 motor.

I just got my 2023 TB 6.2L, and I also noticed it idling a little rough, until I put premium in. Runs super smooth now and I will use premium from now on!

 

[R3D1]

Use what the manual says. The people who designed the engine wrote the book. Octane ratings have to do with the point of detonation. If you use the wrong octane you're causing the fuel to combust at the wrong time of the stroke cycle in the cylinder, which leads to the computer adjusting timing, retarding knock, decreasing power, all while your mpg suffers. This all could cause your emissions to be more dirty those causing issues with your oxygen sensors and catalytic converter.

You got some of the info right. Sort of.

Variable valve timing and the computer look at what fuel is available and adjust from there. Higher octane allows the computer to advance timing. That will allow the engine to produce more power. I remember setting the timing with a timing gun and moving the distributor. Current engines have computer controls and do that automatically taking readings multiple times in a very few seconds.

What does that mean? Well, if the octane is too low your engine will need to retard the timing to prevent knocking and save the engine. This retard of timing will lower the power output. Can it run on 87? yes and it does. But those numbers on the window sticker are based on higher octane numbers. As most of us have found out they are quite optimistic compared to real world numbers.

So what do we do? If you experience no problems with your truck then run what you want. I use higher octane (either 91 or 93) to advance the timing. Where this becomes an issue is when the engine runs at the very bottom of the timing retard scale and can't go lower. Now we have parts (mechanical) straining to do what the computer (software) tells it to do. Big potential for problems. No matter how many times the AFM/DFM runs its calculations per second, the mechanical side simply cannot keep up. This is what many may be experiencing with the engine problems including the failed lifters.

My solution is to run higher octane. The engine can run at an advanced timing level higher than any octane currently available at the pump. The 87 octane is dependent on hitting that number with ethanol and there are a bunch of variables when it comes to that.

Some stations (blender pumps) have problems with the ethanol delivery and/or pump that delivers ethanol to mix with the gasoline. Gas and Ethanol are mixed at the pump. So if you use 87 you may be getting even lower octane. This happens at pumps that offer multiple types of ethanol blends like E10, E15, E...

Splash blending occurs at the refinery and is how most pump gas travels to the station. Even that is skewed to be less that 10%. With real numbers being around 8%. Ethanol has a higher octane than gasoline so they are blended to achieve the number at the pump.

Do a little research on your own, quite a few industry sites available and a few others with engineers who do this chemistry for a living. Theory and application sometimes don't always agree with each other. Real world stuff. I wouldn't call it russian roulette with your engine, but a bad tank of fuel can give you lower octane than the timing can be retarded to process.

 

[islandnewfie]

The GM 6.2L L86/87 is a high compression engine (11.5:1), thus recommends premium fuel. If you use regular fuel the compression of the engine alone can ignite the fuel before spark, thus causing rough idle and engine knock. Yes, you can run regular fuel in these engines, but they are less efficient, and as mentioned by R3D1 will retard the timing to compensate resulting is less power and efficiency. Running premium is not only recommended but you will also get more miles per gallon, more bang for the buck. Pretty much all high compression engines recommend premium fuel. Unlike the 5.3 and 2.7 which are lower compression engines and use regular fuel.

 

[travelinscout]

I noticed a big difference switching from 87 to the 91 in my 6.2. Better MPG, and much smoother running.

 

[GETGONE]

Even dropping to midgrade 89 my MPG dropped from 15.5 with 91 premium to 14.2.

 

[2KWIK2C]

Like in a post many moons ago on here. Premium is all that we buy! Way less expensive in the long run! My ladies vehicle and that is twin turbo, so no using anything else other than premium. All our toys recommend premium as well.! CAN'T GO WRONG!

 

[crayonmagic]

the owners manual on my 2025 recommends 87 octane on 2.7L and 5.3L, and 91 octane on 6.2L

 

[Mike Edwards]

I'm no expert, but since I've been tuning my truck (and various other GM's) with HP tuners I know a bit about how the ECU uses octane. There is no direct octane sensor on the truck. Octane indirectly affects the knock sensors.

In GM ECU's there is a base (high) timing table and a low octane table. The ECU defaults to the base timing table and only shifts down to the low octane table if the knock sensors detect knock. The low octane table varies, but on my 2020 it's 5-9 degrees less timing than the high octane base table. There are rates at which it switches between the two, but in factory configuration it's pretty quick. If it picks up knock it pulls timing out for less than a second then ramps it back in in less than a second. If the knock is severe, it could come out for a longer time, but it's still measured in seconds.

Our trucks knock sensors are extremely sensitive. They're measuring some minor level of knock almost all the time. Like 1 to 2 degrees Some of it is real, some of it is false (just other noise). The knock sensors are basically microphones. For my truck (5.3) when naturally aspirated, I saw little difference in knock in datalogs with 87 vs 93.

87 and 93 offer the same energy content per unit mass, so running 87 makes the same power as 93 as long as the timing stays the same. The timing stays the same if the knock isn't increased. If the base timing table is maximized for 87 octane it shouldn't see any significant knock with 87. If the base table has been maximized for 93 and you run 87 it's probably going to see more knock and spend more time in the lower timing table and thus make less average power. The amount of power the engine makes per volume of fuel directly correlates to fuel economy and knock and octane don't affect volume.

My opinionated cliffs notes: If your truck was tuned from the factory to run 87, running 93 offers no meaningful mileage or power increase.

 

[The Raven]

You got some of the info right. Sort of.

Variable valve timing and the computer look at what fuel is available and adjust from there. Higher octane allows the computer to advance timing. That will allow the engine to produce more power. I remember setting the timing with a timing gun and moving the distributor. Current engines have computer controls and do that automatically taking readings multiple times in a very few seconds.

What does that mean? Well, if the octane is too low your engine will need to retard the timing to prevent knocking and save the engine. This retard of timing will lower the power output. Can it run on 87? yes and it does. But those numbers on the window sticker are based on higher octane numbers. As most of us have found out they are quite optimistic compared to real world numbers.

So what do we do? If you experience no problems with your truck then run what you want. I use higher octane (either 91 or 93) to advance the timing. Where this becomes an issue is when the engine runs at the very bottom of the timing retard scale and can't go lower. Now we have parts (mechanical) straining to do what the computer (software) tells it to do. Big potential for problems. No matter how many times the AFM/DFM runs its calculations per second, the mechanical side simply cannot keep up. This is what many may be experiencing with the engine problems including the failed lifters.

My solution is to run higher octane. The engine can run at an advanced timing level higher than any octane currently available at the pump. The 87 octane is dependent on hitting that number with ethanol and there are a bunch of variables when it comes to that.

Some stations (blender pumps) have problems with the ethanol delivery and/or pump that delivers ethanol to mix with the gasoline. Gas and Ethanol are mixed at the pump. So if you use 87 you may be getting even lower octane. This happens at pumps that offer multiple types of ethanol blends like E10, E15, E...

Splash blending occurs at the refinery and is how most pump gas travels to the station. Even that is skewed to be less that 10%. With real numbers being around 8%. Ethanol has a higher octane than gasoline so they are blended to achieve the number at the pump.

Do a little research on your own, quite a few industry sites available and a few others with engineers who do this chemistry for a living. Theory and application sometimes don't always agree with each other. Real world stuff. I wouldn't call it russian roulette with your engine, but a bad tank of fuel can give you lower octane than the timing can be retarded to process.

You also got some of that info right, sort of.

Modern engine management is constantly adjusting timing, all the time, no matter what octane you use. The system will advance timing until knock is detected (via the knock sensor, which can detect knock far in advance of when it is audible to even the most trained human ear) and then back off a degree or two, then advance again until knock is detected, then back off, and over and over and over continuously. Thus, in theory, a higher octane fuel SHOULD allow the system to advance timing further than with plain 87 octane fuel and CAN create additional power or better efficiency. Keep in mind that with "additional power or better efficiency" we are talking fractions of a HP or MPG.

The problem for us is that this is all the theory, the "in a vacuum" example. We don't use our trucks "in a vacuum", we use them in the real world...and in the real world there are hundreds of other variables that affect the power and efficiency you get out of the fuel you use. The end result of this is that it's not likely you are going to see appreciable power or efficiency gains from higher octane on our NA V8's. If you ARE then you very likely have an issue that premium fuel is masking. Higher octane is not a fix for anything at all...yes it can stop knock...but you shouldn't be hearing knock even on the 6.2 running 87 octane...the engine management system in these trucks has MORE than enough range built in to be able to compensate even for crappy 87 octane fuel. So there should be no knock outside of very extreme use cases (like towing near the limit in extreme heat on a long climb type of extreme). If you are hearing audible knock while running 87 octane on any of the engines available in our trucks, you have an issue that needs to be looked at (or you are pushing your truck too hard and need to stop). Don't try to mask it with premium fuel unless you want the problem to wait until after your warranty is expired. If you have a dealer that tells you "the problem is the fuel grade" then you need to find a different dealer.

All that said, if premium fuel in your truck helps you sleep at night, go for it. It definitely won't hurt anything (assuming you didn't have knocking on 87 octane that is). But it also makes ZERO difference when it comes to the lifters or any other mechanical component. I've done the premium fuel "test" in every vehicle i've ever owned and it has never yielded any advantage of any kind in any of the NA vehicles i've tried it in. In my current TB, I got the exact same fuel mileage on 93 that I get on 87, and it was right on the EPA estimates (in stock form, of course).

Comical side note - this exact same thread (you should be running premium fuel!!) exists on every automotive forum i've ever been a member of since the beginning of internet automotive forums, and most of those threads are still raging today. This and the "oil weight thread" are the "legends" of the internet automotive forum.