93 Octane tune at high altitudes

[customyota]

Hey all, I live in Wyoming, high altitude and cool for most of the year. The highest octane fuel available here is 91, and I was reading that it's primarily because the high altitude (5000+ ft) means that 93 isn't necessary. The lower density air makes for richer overall fuel mixtures, I suspect. Given this, would it be safe to run a tune meant for 93 octane on the available 91 octane fuel?

[swarb]

Originally Posted by customyota

Hey all, I live in Wyoming, high altitude and cool for most of the year. The highest octane fuel available here is 91, and I was reading that it's primarily because the high altitude (5000+ ft) means that 93 isn't necessary. The lower density air makes for richer overall fuel mixtures, I suspect. Given this, would it be safe to run a tune meant for 93 octane on the available 91 octane fuel?

You are right about the density.
No real way to know unless you data log it.
Since you don't have much choice, I'd say it is safe since the ecu has some correction in it. It might pull some timing if its not running well.

[steve99]

Originally Posted by customyota

Hey all, I live in Wyoming, high altitude and cool for most of the year. The highest octane fuel available here is 91, and I was reading that it's primarily because the high altitude (5000+ ft) means that 93 isn't necessary. The lower density air makes for richer overall fuel mixtures, I suspect. Given this, would it be safe to run a tune meant for 93 octane on the available 91 octane fuel?

modern cars including this one have Atmospheric pressure sensors , mass air flow sensors and 02 sensors and a feedback control system (closed loop fueling) so its able to make adjustments for changes in air density and atmospheric pressure changes.

The stock tune is meant to run best on 93 but will accomodate 91 fuel at slightly lower performance.

If you have a performance aftermarket tune in the car meant for 93 then you need to run 93 or get your tune changed to a 91 compatable tune if you want to run 91 all the time

[JoeC]

Originally Posted by steve99

modern cars including this one have Atmospheric pressure sensors , mass air flow sensors and 02 sensors and a feedback control system (closed loop fueling) so its able to make adjustments for changes in air density and atmospheric pressure changes.

The stock tune is meant to run best on 93 but will accomodate 91 fuel at slightly lower performance.

If you have a performance aftermarket tune in the car meant for 93 then you need to run 93 or get your tune changed to a 91 compatable tune if you want to run 91 all the time

I don't think the car is just accommodating 91 octane here at altitude. It has the same behavior as 93 with regard to knock or early detonation. I don't think I've ever even seen 93 in CO or WY.

With that said, I don't know nearly enough about custom tuning to advocate running a 93 tune at high altitude.

[steve99]

Originally Posted by JoeC

I don't think the car is just accommodating 91 octane here at altitude. It has the same behavior as 93 with regard to knock or early detonation. I don't think I've ever even seen 93 in CO or WY.

With that said, I don't know nearly enough about custom tuning to advocate running a 93 tune at high altitude.

the main difference between 91 and 93 tunes will be the ignition timing

[aagun]

the ECU is smart enough to lower ignition timing and keep the engine at safe points . takes off any knocks from it