Best octane fuel for fuel eceonomy? (5.3L only)

I've searched and read many posts, but I'm looking for more peoples' experiences.

What octane gas yields you the best mpg in your Burb / Tahoe / Yukon? Which grades have you tried?

Please only respond if you have a the 5.3L since the 6.2L requires premium.

BlackBear recommends 89-octane due to the compression ratio of this engine. I've run both 87 and 89, but I'm not sure I ran 89 long enough to see the changes. Would you see them over 1 tank?

Thanks all!!

what does the owners manual recommend.

The owner's manual recommended a minimum of 87-octane. BlackBear performance is a pretty reputable company (especially on this board) that disputes that - they recommend 89 or higher.

you can most likely use either one as long as there is no pinging under load.

I have a tune (not BlackBear) on my 5.3 running 93 and get better MPG than stock on 87


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Octane and the amount of energy in the fuel are two different things in my opinion. If I am not mistaken, Octane indicates how resistant the fuel is to premature detonation due to compression which is why the higher the Octane is, the less pinging you get. This is why higher compression motors, like the 6.2, need higher octane fuel. There is a small correlation between octane an mpg, but if you put 93 octane in a motor designed to run 87 octane, you won’t see a big change in mpg’s.

Typically, you will get better mileage with a furl that has less alcohol, but more power with more alcohol.

@swathdiver has a thread where he discusses this at length.
https://www.tahoeyukonforum.com/threads/useless-information.97483/page-85#post-1456757

If you're engine is stock and not tuned 87 is all you need. If you have a tune then you need to run whatever it has been tuned for be it 87, 89, or 93.

Trying to get better mileage by switching octane is a fool's errand.

The octane rating does not change the amount of energy in a gallon of gas. The octane rating is merely a quantifiable measure of how fast the fuel burns. Higher octane burns slower.

Any purported "increase" in mileage using a higher octane is easily offset by the higher cost, negating the benefit.

Never mind the fact that these things were/are built for a myriad of reasons, the least of which is economical use of fuel. Giant vehicle, horrible aerodynamics, large V8 engine. You want good mileage? Buy a Prius.

...

Totally agree with Texasdaddy above.
It's a waste to buy higher octane if your engine doesn't require it..
BUT, a company like Blackbear has tuned so many of these vehicles, that
they have probably seen that 87 octane, at certain loads, probably causes
the knock sensors to see knock - therefore reducing timing AND adding fuel....
because that's what the ECM does when there is detonation/pre-ignition to
save the engine from self destruction.
So ... if you run 89 OCTANE, you will stay out of those circumstances avoiding
the extra fuel rush and timing retard... You won't be able to hear it or notice it..
And that's the beauty of the modern engine and electronics
Run the 89.. esp now it's cheap and see if it helps with YOUR driving condtions
IF you are at say 1200 ft above sea level it may not make any difference.
But if you are at 200 ft and maybe your local gas isn't that great... you may be
adding a lot of life to your engine