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The Ascent should be run with 87 octane in all conditions.
 

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Is 87 octane the definitely the lowest octane to be used in the Ascent?
87 octane, in all areas, at all elevations, during all seasons.
 

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Waiting on my delivery but on my Crosstrek it does have more pep and a little more MPG on premium. Cant say if the ascent would benefit from this or not. Will say you aint gonna gain enough to makeup for the $1ish premium to go from 87 to 93 but never run under 87.. Im surprised it can run as good as it does on 87 with the turbo.
 

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I run mid to high grade when towing in hot weather in the mountains. Sure it will run on 87, but i tend to think 87 is more prone to detonation and turbo 4s are already inherently prone to this with 87. The ECU will adjust timing on 87 to avoid it and will also dump in more fuel to cool the engine, but will i get maximum performance on 87....i'm not sure and figure running mid to high grade is best when towing with these types of engines.
 

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I run mid to high grade when towing in hot weather in the mountains. Sure it will run on 87, but i tend to think 87 is more prone to detonation and turbo 4s are already inherently prone to this with 87. The ECU will adjust timing on 87 to avoid it and will also dump in more fuel to cool the engine, but will i get maximum performance on 87....i'm not sure and figure running mid to high grade is best when towing with these types of engines.

Turbo engines have a lot more safeguards in the ECU to prevent detonation. I have to wonder if anyone has specs on what the max compression at max boost will hit.


And for reference I gained 3-4MPG with premium in my crosstrek.
 

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When 1st got the Ascent i was towing on 6% grade and temps i think close to 90.
It was struggling for sure and ever since then I've been using 89-93 in those types of conditions and it's been fine. I'm thinking it was do to the gas now and the ECU limiting the timing and dumping more fuel to help cool it down.
 

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When you're working a turbo motor harder than usual, it's good to increase the octane.
Why do you feel that way? This engine isn't designed to require higher octane (slower burning) fuel, unlike many of the turbos on some other brands or older in design where there is higher compression and pre-disposition to pre-detonation. (knocking)
 

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Why do you feel that way? This engine isn't designed to require higher octane (slower burning) fuel, unlike many of the turbos on some other brands or older in design where there is higher compression and pre-disposition to pre-detonation. (knocking)
Since higher octane burns slower, it burns slightly cooler, offsetting the extra heat generated by running it hard. Also, pushing the engine hard increases the chance of pre-ignition, which would cause the ECU to retard the timing, reducing your power. Running higher octane greatly reduces chance of pre-ignition, so no timing retard & no power reduction.
 

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Resurrecting this post. To counter what SubieDriver said, COBB Tuning has done a massive amount of tuning and research on the Ascent ECU as it relates to different octanes. They found there is ZERO effect on the stock map utilizing higher than 87 octane fuel. Zero, as in nothing. No effect. No benefit. The ECU does no dynamic adjustments based on higher octane fuel.

So in regards to the blanket statements about using higher octane is always better, that’s simply not true.
That is only true if the ECU map has been specifically designed to either: 1. Take advantage and dynamically adjust to higher octane or 2. Requires higher octane as the map has been designed with bare minimum high octanes in mind (i.e. 91/93oct)
In a stock Ascent, 87oct all day.

Once you go with a custom tune on the Ascent, all the above no longer applies.

Octane recommendations and requirements are completely vehicle-specific. Cannot make blanket statements. There’s one caveat in all of this and that is if there is a KNOWN increase in the QUALITY of gasoline that is only in the higher octanes available to a particular area.

Everything else is flushing money down the toilet just for some “feel good” nonsense.
 

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^^ what he said, with one added thought...

while you may not see a performance difference with a higher octane, part of the price difference is the premium detergents and additives in the premium fuel. So my question is if it may be beneficial to run a tank of 93 thru every once in a while for that reason?
 

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I think a lot of research would need to be done as opposed to buying the gasoline marketing benefits / hype on said gasoline. If there are indeed real, tangible benefits in said gasoline, it’s probably something that is realized over repetitive, consistent, prolonged use (many tanks) as opposed to every once in a while.
 

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^^ what he said, with one added thought...

while you may not see a performance difference with a higher octane, part of the price difference is the premium detergents and additives in the premium fuel. So my question is if it may be beneficial to run a tank of 93 thru every once in a while for that reason?
The additives are found in Top Tier fuels regardless of octane.
 

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The additives are found in Top Tier fuels regardless of octane.
I don't think I've ever noticed the Top Tier logo at Exxon or Sunoco but now I'll actually look for it. Good info, thanks! Does anyone actually use Citgo or BP? They're always $ .10-.20 higher priced than everyone else from what I've seen.
So using Top Tier gas is probably more beneficial than using higher octane is my take on this.
 

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Manufacturer recommends 87 that’s what I’m sticking with.
Down the line what harm will come to the engine,if any,when going back and forth on the different grades?...something to think about.?
 

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I don't think I've ever noticed the Top Tier logo at Exxon or Sunoco but now I'll actually look for it. Good info, thanks! Does anyone actually use Citgo or BP? They're always $ .10-.20 higher priced than everyone else from what I've seen.
So using Top Tier gas is probably more beneficial than using higher octane is my take on this.
while traveling I am mindful of the top tier fuel brands. Locally I know where they all are and generally the comparative prices. With my older vehicle, I used to purchase fuel from the grocery stores since I received a discount but I was experiencing poor performace and contaminated fuel. Now all my vehicles use only top tier fuel. While traveling I can request through google to find a top tier fuel station and it pops up on the map along my route.
 
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