Which Gas Grade to Use for the 5.3 Engine

[snowstorm]

I got a 2024 SLT, 5.3 I have been filling Premium, but I have been reading and hearing about mixed opinions on whether it's okay to go with 87. Is that true?

 

[Marky Dissod]

87 is just fine, especially if you drive gently / gingerly.
The harder you drive, the more strongly 91 is recommended - 'but not required'.

 

[Blueinterceptor]

5.3 is tuned for 87.

 

[BruceW]

Octane is all about pre-ignition. If you don’t hear it when your accelerating then you don’t need a higher octane.

An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without undergoing pre-ignition. The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates gasoline's resistance to detonating under pressure without a spark.

 

[Marky Dissod]

I got a 2024 SLT 5.3L. I have been filling Premium, but I have been reading and hearing about mixed opinions on whether it's okay to go with 87. Is that true?

To get technical, GM has been using two separate octane - as in, High Octane & Low Octane - spark timing tables since 1997.
So, if you prefer how it runs on 91 octane, then do so - especially if your truck works or plays HARD.

On the other hand, every 5.3L was tuned by GM to run well on 87 octane.

 

[tom3]

I guess I'm old school on this but I think with the 11 : 1 compression ratio and getting 355 horsepower out of 326 cubic inches I want better gas in mine. I run at least mid grade and if I'm near a Sam's Club I fill up with their premium. I do get pretty good gas mileage on trips and see 80 mph quite a bit on the road.

 

[Marky Dissod]

I guess I'm old school on this, but I think with the 11 : 1 compression ratio and getting 355 horsepower out of 326 cubic inches I want better gas in mine.
I run at least mid grade and if I'm near a Sam's Club I fill up with their premium.
I do get pretty good gas mileage on trips and see 80 mph quite a bit on the road.

Reason why this ol' skool thinking is out of date, is that 11-to1 static compression fails to account for any of the following:
the 'hottest cylinder' is no longer #7, it's #1 - except #1 is now closest to the H2Opump
there are no exhaust valves adjacent to each other
improved quench
better cylinder-to-cylinder coolant routing and steam venting
and the cherry on top that's bigger than the sundae:
fuel pressure went up from 4 bar to 150 bar,
which atomizes the schidt out of the fuel so well,
cylinder temps actually drop during the injection phase - oh
that injection phase occurs during the compression stroke

Just sayin, no need to fear 87, it's FINE.
91 octane fuel is ALWAYS better than 87, but it's not needed for any 5.3L.

 

[E_S_D]

The recommended fuel grades start on page 284 of the owner's manual, and page 285 states:

Recommended Fuel (5.3L Engine)

For diesel engine vehicles, see “Fuel for Diesel Engines” in the Duramax diesel supplement.

Regular unleaded gasoline meeting ASTM specification D4814 with a posted octane rating (R+M)/2 of 87 or greater is recommended. Do not use gasoline with a posted octane rating of less than 87, as this will result in reduced performance and driveability. If heavy knocking is heard when using gasoline rated at 87 or greater, the engine needs service.

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