How to change fuel octane?

[hthy]

How to change fuel octane E38 5.3L to 87 octane?

Thanks

[5FDP]

There is no drop menu to change fuel grades from like 87,89,91,93 etc etc.

That motor and pcm is already built to run 87 octane from the factory, so I'm not sure what you want to know.

[hthy]

Thanks for reply

how I can change to less than 87 like 85 or 83?

[5FDP]

You'd have to figure out a way to tune around it, watching fueling and timing and knock. All of that needs to be watched to make sure it doesnt hurt the motor.

I'd personally never run lower than 87 octane, even GM says the lowest octane you should run safely is 87 octane.

[hthy]

Thanks for help