[RobZL1]

yes. this is what I was trying to say. It takes much longer for the knock learn factor in the tune to go "up" toward the high octane advance table, than it does for it to go "down" toward the low octane advance table.

[SuperSnake1972]

The reason you're not finding any 93 octane is because of the higher elevation. And the onboard computer adjusts for both the elevation and octane rating.

[6spdhyperblue]

Originally Posted by James6speed

Revisting this. After I have ran without issue for 10k miles and no knocking on Shell 89 octane, I decided to change to 93 Shell. I have noticed no difference at all in power.. I am switching back to 89 at this point. The internet keyboard pounders we're wrong as I suspected. The computer does automatically draw back with DFI to adjust for the octane and the power difference seems to be negligable. I daily this car, so an extra $20 bucks in my pocket for nothing is good enough for me.

You talk like you took it to a dyno or a drag strip. If you’re getting no knock or sluggishness for commuting purposes, good for you. Just don’t be surprised when you get wasted by a m4 or 5.0

[Gen6cyl]

If your computer is pulling timing it is detecting knock. Maybe it can pull enough to run okay. I had rather run 93 , not have any knock and have the timing advanced as much as possible.

[Alan47717]

Originally Posted by SuperSnake1972

The reason you're not finding any 93 octane is because of the higher elevation. And the onboard computer adjusts for both the elevation and octane rating.

91 octane is prevalent in the SW because NA engines make less power at altitude (lower effective compression rate).

When I lived in Deming, NM (4300 ft elevation) 87 wasn't available at most stations. The choices were 86, 88 or 91 typically.

In the Tucson area (22 to 2300 ft elevation), a NA engine is down roughly 6% in power (rule of thumb is 3% per 1000 ft). Boosted engines are a different story of course, keeping the knock sensors busy.