Which Octane in Colorado?

[MojaveBart]

I'm going to apologize asking this. I did a search and while I saw a few people from CO answer, not enough to be sure. So what Octane should I be using in my 2020 JT Mojave? The User Manual says no less than 87 Octane. And the Dealer I bought it from said the same thing.

The pumps I visit in Metro-Denver only has 85, 89, and 91. The Dealer said 89!

I saw some posts where CO owner's are using 85.

So is it okay to use 85 Octane?

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[Br4hm4]

I have been running 85 here in Colorado for almost 13K miles. No issues. "At higher altitudes, the thinner air compensates for the gasoline's lower octane, so the engine can usually run without detonation."

 

[InvertedLogic]

85 is likely fine thanks to knock sensors that will detect knock and pull timing. But I run 87 as the manual states.

Here is my unpopular opinion and complete ass-talking: 85 octane as the standard at high altitude states was started when cars were carbureted. With a carburetor, airflow vs carb tuning decides the effective AFR the engine sees. So with less air being drawn in, so it less fuel, all is well. However, modern fuel injected vehicles have variable timing on the fly, air flow sensors, injector duty cycle tables, and o2 sensors. It knows exactly how much air it's getting - even at high altitude, and injects the proper amount of fuel according to its fueling table and sets the spark off according to its timing table. My theory is that what likely happens with modern high compression FI vehicles is that thanks to good engine management and knock sensors, the vehicle detects knock when its filled with 85oct, pulls global timing accordingly, and prevents engine damage at the cost of power and efficiency. Whereas if it were filled with 87 and run the ignition timing unmodified, it will yield better power output and fuel efficiency since it's not running at -5degrees of timing or whatever.

Again, this is just my thought process, and certainty does not align with the accepted wisdom that has been around since the carbureted days. That said, here is what a GM engineer has to say about it.

and more from the EPA

https://tap.fremontmotors.com/trusted-auto-professionals/is-85-octane-ok-to-use-at-altitude

So that's why I run 87 when I can, but your engine won't explode if you run 85 like 99% of other people.

 

[InvertedLogic]

More to support my line of reasoning: https://www.denverpost.com/2006/10/16/some-knock-states-lower-octane-levels/

The number of cars I hear knocking driving down the street on a hot day in Denver is

 

[WK2JT]

More to support my line of reasoning: https://www.denverpost.com/2006/10/16/some-knock-states-lower-octane-levels/

The number of cars I hear knocking driving down the street on a hot day in Denver is

I guess nothing came of that December meeting considering the article is from 2006. Government... gotta love it. Lol

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