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I'm still waiting for a map that will let me run Rockies Regular 85.
 

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Just for shit and giggles, let's watch this. Done by CBC 4 years ago. I couldn't believe how so many people are clueless about gas grades.

 

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Just for shit and giggles, let's watch this. Done by CBC 4 years ago. I couldn't believe how so many people are clueless about gas grades.

Thanks Tuanvo- i 've been searching for that story since this topic came up- i thnk it came out of Toronto-Great stuff Thanks Jeff
 

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Many argue that at higher elevations such in Colorado you can use what we have as 85 octane which from what I have read is effectively 87 at sea level. So far I have only fueled up with 87 which is the Subaru recommendation but of course they make one grade recommendation for the entire nation. If I drive or plan on driving a tankful only at elevation could I use Colorado 85 octane?

Thoughts?


As noted above, some would suggest the following:
You should be using 89 octane here in CO if your car recommends 91 Octane.
Octane loses 2 points in the transition from sea level to our 5200+ feet here in the Denver area.


So 87 octane in NYC is 85 octane here in CO.
89 Octane turns into 87 at high altitude.
91 octane becomes 89.
93 becomes 91
 

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Turbocharging as implemented in the Ascent compensates for the reduced atmospheric pressure in CO, so you need to stick with the sea level octane recommendation, which is 89 87 for the Ascent's turbocharged engine.
 

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Turbocharging as implemented in the Ascent compensates for the reduced atmospheric pressure in CO, so you need to stick with the seal level octane recommendation, which is 89 for the Ascent's turbocharged engine.
I personally have always put in the Subaru recommendated octane but there are engineers who believe that even with today's modern vehicle computers that you can go 2 octane points lower in higher elevation. I do not have the engineering background to argue one way or another. Those engineers obviously are aware of the computer compensations.
 

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Yes, you can go two octane points lower in normally aspirated engines because the lower ambient pressure reduces the manifold pressure. The Ascent's turbocharger is in a closed loop that determines manifold pressure independent of ambient atmospheric pressure. It will be the same in CO as it is at sea level, so 89 87 is still recommended/required.
 

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I personally have always put in the Subaru recommendated octane but there are engineers who believe that even with today's modern vehicle computers that you can go 2 octane points lower in higher elevation. I do not have the engineering background to argue one way or another. Those engineers obviously are aware of the computer compensations.
Sorry, but they're laughably wrong, which is why there are no car manufacturer engineers who agree.

It's 87 octane at any altitude, all the time.

As for the Ascent specifically, it's not even operating in peak boost range under normal test altitudes, meaning it's got a lot more it can do to make up for less oxygen at higher altitudes. So, like Merope said, it sucks in as much air as it needs for its 87 tune, regardless of the altitude.

 

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Oops. I was getting my numbers mixed up. I meant 87 octane is what the Ascent requires at all elevations. 85 is the swill that passes for regular in CO and is not adequate for the Ascent's turbocharged engine. I went back and corrected those two posts.

Using gas of insufficient octane can cause detonation (AKA knocking) which is harmful to the engine. It's true that pretty much all modern engines of have knock detection and will retard the timing if knocking is detected, which will ameliorate if not totally prevent damage. Despite that, it's far better to prevent the condition by using an adequate octane fuel. Higher octane than that, in itself, provides no benefit.
 

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I'm really not interested in more power and driveability is fine as is, or at least I've gotten used to it. What I'm really waiting for a COBB tune that allows using 85. It'd pay for itself in something like 100,000 miles.
 

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I'm amazed they managed as much power with 87... I would be surprised if anyone got 85 to work adequately.
 

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^^^ sounds like you're throwing down the gauntlet and challenging COBB to do it.

I was just kidding and would not buy a COBB just for the purpose of running 85. After having vehicles that required premium for 16 years, I was looking forward to being able to run regular, which, unfortunately, the Ascent can't in CO, cuz CO regular is 85.
 
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