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2022 Subaru Outback Wilderness
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You won’t hear it, the ECU will detect it and retard timing before you notice to avoid damage. 87 is the minimum, who knows if that gas has been sat at the station for some time and degraded to a lower octane? Personally I don’t get spending >$40k for a performance version of a car then saving a couple hundred bucks a year to leave a portion of that performance on the table (+ risking the longevity of the engine by running it at the extreme end of its performance envelope).
The gas station QuikTrip (QT) has a very high turnover rate for their gas tanks. They generally refill every 2.5 to 3 days so no stale gas can be expected there. Also (QT) is top-tier too. When there is little freeway traffic I can open the Wilderness up, and she scoots pretty fast. I have to watch my speed with her since it is almost too easy to exceed the legal speed limits. On a long local stretch of road, I set the Lane Assist and motor at the speed limits. I have had people blow past me, and get nailed by the local PD. (I know where they hide. 😆 )
 

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2020 Onyx
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I'm not sure why, but on the Ascent that tows 5000 pounds, there is no mention in the owner's manual about 91 octane while towing. On the Ascent forum almost everyone uses 87 (top tier) including when towing and have not reported any octane-related issues or overheating. Although I personally use 91 I don't think it's a mistake to use 87. For whatever reason, LSPI has not been an issue on Subaru direct injection motors, and the transmission seems to be programmed to prevent lugging, downshifting before boosting it seems to me, which is my theory on why some people complain of a delay in throttle response.

I think Subaru is smart enough to design an engine that will run safely on the octane that they specify - they've been making turbocharged production cars for almost 40 years.
 

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2018 Outback 3.6r touring //// 2004 Wrx wagon 5mt SOLD
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153 Posts
Just run premium and keep the car happy. If you can afford to buy a brand new turbocharged car, you can afford to run premium fuel. I bought my 04 wrx when I was 25 and was able to afford to buy premium fuel, no problem. Never noticed a hit on my bank account. I really dont understand the skimping here and there between fuel grades.
 

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2022 Subaru Outback Wilderness
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354 Posts
Where I live in Georgia, we are at a much lower altitude than, say, the folks out west in nose bleed territory. Many years ago, we noted the octane differences and used the higher octanes in Colorado, Utah, and Wyoming. We had a Ford E-350 with a V-10 motor at the time.

The 2.4L Turbo will perform differently in other country areas along with the different fuel blends. What fuel blend we use here in Georgia differs during the winter and summer months.

For the moment, CoCo is a happy Wilderness and motors along happily without compliant or idiot warning lights.
 

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2018 Subaru Outback 2.5i Premium
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148 Posts
87 in GA heat is going to have your engine riding the knock sensors and pulling timing. Why bother getting the 2.4 if you’re going to hold it back with low octane gas?
Higher octane doesn't make any difference here in the heat of South Carolina. It seems to me that many people look for reasons to use higher octane, believing there's something magic about it, and hence they convince themselves that it performs better, even when it doesn't.
 

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2020 Onyx
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There's a middle ground between saying higher octane does nothing, and saying that it's everything. This is regarding the 2.4 direct injected turbocharged engine, not a 2.5 naturally aspirated port injected motor.

On 87 octane Subaru says to ignore the knock that you hear. It does knock under higher load like going up a steep incline. There may be a small amount of knock retard, but it won't damage the engine as it's designed to cope with 87 octane. But if you're towing it does say to use 91 so octane does matter. All you have to do is be reasonable in your expectations - there's no right or wrong octane as a blanket for all situations - this is what Subaru is telling us in the owner's manual.

High load like towing does prefer higher octane. Low load driving doesn't require it.
 

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2022 Outback Wilderness with moonroof package
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In your case, I would use 91. As a side, my dealer said to use 89 on the 2.4 it helps gas mileage. I still think BS.
Not so sure . . . . Just ran a tankful of 89 in mixed town/highway driving after only using 87 for the first seven months I've had the OBW. Initial impression is perhaps 1 or 2 more mpg and a bit more perkiness in the engine. Makes it at least worth while to run 89 a few more times to see if that impression holds up.
 

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2021 XT Touring Popular package #2 OEM Hitch
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462 Posts
I have only used 87 and i tow i have not had any issues in 5400 miles. 87 is 3.34 . They dont sell 91 near me its 93 at 4.39 or 105 at 7.25
 

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2020 Onyx
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Where I am the price difference isn't so steep - only because Regular is so expensive here in Hawaii, and our premium is 92 - but I'm just used to buying premium so to me it's business as usual.
 

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I wouldn't worry about it, that's what the engine management computer is for, it will adjust the engines timing and other things to compensate for lower octane gas. If you are going to go out and beat on the car one way or anther or pull a trailer then I'd pop for some better gas.
never go below the manufacturer's recommended octane.
 

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'21 Onyx Ice Metallic Silver
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111 Posts
Not around here. Just drove by a Shell station today and 91 octane is $5.09 😢
Ouch!

Cheapest around here is $4.69 for 91.

I've only ever put 87 in my Onyx. I'd be curious to experiment with 91 just for the **** of it, but I've also had no issues so far, so why pay more if I don't need to?
 

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Does anyone notice that the octane stickers say "Minimum Octane Rating" on them?

Doesn't that mean you can actually be filling-up with a higher octane than you're paying for?
Yes, it's not only possible but likely. Indulge me for a moment.
The fuel in the big rig that delivers fuel to the station is all one type/kind/octane rating. What determines what you pump out of the ground into your car is the additives added to the fuel when the driver is dumping it into the ground tank. If the mix is a little off or if the estimated fuel remaining in the tank isn't perfectly accurate this can throw off the ratios. What you wind up with is something close to 87 octane. The promise is 87 octane minimum, they use the word for a reason.

The same can be said of alcohol content. A maximum alcohol content of 10% doesn't mean it's 10% when the fuel comes out of the pump, that's a max allowed and what the target of the distributor is. I can't test octane rating but I can test alcohol content and can verify I've never found alcohol over 10%. It's usually 7-9%.

How much higher the 87 rated fuel is is random. It could be a point or two but you aren't going to get 92 out of the 87 dispenser. 88 or 89? Likely Not really enough to make a big difference.
The Department Of Weights And Measures checks fuel quality in the state of Indiana so I assume it's the same in most states. The purpose is to verify the product meets the posted standards.
 

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Bear with me, I eventually get to a point.

My Cruze has the 1.4L turbo that calls for 87 octane and uses approximately the same 16 psi boost pressure as the FA2.4. I've never actually heard knocking from it.
BUT when I do full throttle acceleration, in 3rd gear from 2000 rpm it often has a slight, but noticeable, stumble around 3500-4000 rpm when using 87 octane. With 91 that stumble is almost never present.
Monitoring the boost pressure with my scan tool suggests that some of the stumble is due to sloppy boost pressure management as the turbo spools up to maximum allowable pressure since the stumble coincides with reaching max pressure. If I more gradually ease into full throttle and let it reach maximum boost before going to 100% there usually isn't any hesitation. I suspect there's a spike in the boost pressure that causes a slight knock at the same time the wastegate is trying to level out the pressure.
This stumble doesn't ever happen in 2nd gear despite a faster ramp up to max boost which should be more difficult to level out. With 2nd gear the engine obviously isn't fighting as hard, gets to higher rpm more quickly, and doesn't last long enough to really build up heat the way 3rd gear does, hence why I believe the stumble in 3rd isn't solely down to boost management.

Finally getting to my point. A V1.4L turbo has far less heat management capability than a 2.4L boxer - MUCH smaller volume cylinders that are MUCH closer together, yet the 1.4L needs to be pushed hard to build up enough heat to suggest the engine is having to fight knock.

If you are driving normally there is no way that you're going to build enough heat to cause knocking.
If you're doing something that will produce more engine heat than it can dissipate you're potentially going to force the engine to retard timings, adjust boost, etc to avoid knocking on the regular fuel. If it's a temporary event (going full throttle on a hot day to make a pass) you'll probably never notice the reduced power and it's very unlikely any damage will occur unless there's some other issue with the engine that prevents it from detecting/preventing knock.
As the manual says, if you're towing, or otherwise doing something that's going to build up heat for an extended period of time, then the 91+ octane is going to help protect the engine from having to fight knock and reducing performance.
 

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I'm not sure why, but on the Ascent that tows 5000 pounds, there is no mention in the owner's manual about 91 octane while towing. On the Ascent forum almost everyone uses 87 (top tier) including when towing and have not reported any octane-related issues or overheating.
Does the Ascent have a larger radiator, grille opening, or some other means of better dissipating heat from the engine/transmission?
Something like a more powerful water pump seems unlikely due to the powertrains being identical... but with a different engine compartment the cooling system will likely require some slightly different parts.
 

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2020 Onyx
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In the Ascent the CVT fluid cooler is definitely larger, and probably the radiator as well. Some forum members have both and can do some eyeballing or quick measurements to confirm.

The Cruze 1.4 turbo's compression ratio is 9.5:1 and the non-turbo 1.8 is 10.5:1

Since you do logging, can you verify whether boost pressure, timing, oil temperature, anything changes when switching octane on the 2.4 turbo?
 
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