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2020 Onyx
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One thing that concerns me about using 87 octane is the PCV system. I have a UPR dual stage catch can on my F150 Ecoboost and I get quite a bit of liquid out of it in the Winter. It's mostly water condensate mixed with oil. Just small amounts of oil in the Summer. I have no doubt this sludge mixture coming through the intake valves would reduce the effective octane of the fuel.
I use premium but when you think about it, the 2.4 turbo on regular fuel with SN GF-5 oil (not SN-Plus, not Dexos 1 Gen 2) seemed to have no problem. These older oils were more prone to react with fuel in a way that reduced octane. Using SP/GF-6 gives added protection against that. When I first got the car I was afraid of LSPI but it's been 2 years since it's been used in the Ascent and I do monitor their forum and I'm not seeing any issues.

If you're using SP/GF-6 then the potential harm of reduced octane from oil is decreased. I use premium mainly for the increased detergency for the direct injection fuel injectors in Shell V-Power.
 

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2020 Onyx
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Does Subaru incorporate a catch can on the 2.4 L engine?
no, but the valve covers have a built in air/oil separator baffle system, while it may not be 100% effective it's there. The video below is for an older model but I'm sure the new engines have similar mitigations.

 

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For what it’s worth, I’ve been in an email exchange back and forth with Cobb regarding their future protune product.

It is Cobb’s opinion that the Subaru system runs on the leaner side for emissions and economy purposes and as a result runs a little hotter in the cylinders which seems to cause some knock scenarios.

A richer tune would help if you continued to run 87, but it is their opinion that it would be more advantageous to run 89, 91, or 93 if available to help in those potential knock scenarios.

We did not get into the meat and potatoes over which scenarios could cause the knock more often but they did say it operated differently from the Ascent’s version of the FA24.

In the interest of long term engine reliability, I’m personally choosing to run 93 since it’s priced under 10% more than 87 at my local Costco.
 

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2020 Abyss Blue Pearl OB XT
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For what it’s worth, I’ve been in an email exchange back and forth with Cobb regarding their future protune product.

It is Cobb’s opinion that the Subaru system runs on the leaner side for emissions and economy purposes and as a result runs a little hotter in the cylinders which seems to cause some knock scenarios.

A richer tune would help if you continued to run 87, but it is their opinion that it would be more advantageous to run 89, 91, or 93 if available to help in those potential knock scenarios.

We did not get into the meat and potatoes over which scenarios could cause the knock more often but they did say it operated differently from the Ascent’s version of the FA24.

In the interest of long term engine reliability, I’m personally choosing to run 93 since it’s priced under 10% more than 87 at my local Costco.
You talking about the XT Outback using a higher grade of gas?
 

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2020 Onyx Outback
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For what it’s worth, I’ve been in an email exchange back and forth with Cobb regarding their future protune product.

It is Cobb’s opinion that the Subaru system runs on the leaner side for emissions and economy purposes and as a result runs a little hotter in the cylinders which seems to cause some knock scenarios.

A richer tune would help if you continued to run 87, but it is their opinion that it would be more advantageous to run 89, 91, or 93 if available to help in those potential knock scenarios.

We did not get into the meat and potatoes over which scenarios could cause the knock more often but they did say it operated differently from the Ascent’s version of the FA24.

In the interest of long term engine reliability, I’m personally choosing to run 93 since it’s priced under 10% more than 87 at my local Costco.

Also use Gasbuddy to get deals on premium. I am almost always getting 10-25 cents a gallon off using it and hitting local Shell stations.
 

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2020 Onyx
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Odd that the Ascent and Outback's engine tuning is so different. Aside from lighter weight I can't see why it wouldn't be tuned the same. Both are SUV's with the same stated torque and horsepower and the same transmission, so it's not like we're comparing the upcoming 2.4 turbo in the WRX which obviously would be tuned differently than the 2.4 in an SUV.

Mazda does something to make sure that their intake valves reach 400 degrees F to prevent intake valve deposits. Wonder if running hot on the edge of lean is part of that equation and Subaru is doing something similar? If so, why wouldn't they do it in the Ascent?
 

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Odd that the Ascent and Outback's engine tuning is so different. Aside from lighter weight I can't see why it wouldn't be tuned the same. Both are SUV's with the same stated torque and horsepower and the same transmission, so it's not like we're comparing the upcoming 2.4 turbo in the WRX which obviously would be tuned differently than the 2.4 in an SUV.

Mazda does something to make sure that their intake valves reach 400 degrees F to prevent intake valve deposits. Wonder if running hot on the edge of lean is part of that equation and Subaru is doing something similar? If so, why wouldn't they do it in the Ascent?
Perhaps it's something that changes on the fly as time goes on, in the form of a minor change not noted (most buyers wouldn't care about that statistic like we seem to). There have been minor tweaks from time to time in the same engines across other models.

I do know during my exchanges with SOA following the Ascent's announcement and launch that they are "aware" of the DI buildup issue plaguing other manufacturers and that they were "super lean burn" designs from Audi/VW, which required a walnut shell blasting every 60,000 miles or so. I'm confident that their engineers were able to build a better design for the FA24, and hopefully for the 2019+ FB25DI's. The benefit is that we don't have the first iteration of this engine, so we should have a ~2 year heads up from the Ascent drivers if things start to cause problems down the road.

From what I'm understanding, the "upper engine" or "carbon clean" cleaner type services are good for minor cleaning but will not be effective if the carbon buildup continues to the point of actual engine problems or check engine lights, which would require more... intense... cleaning procedures. I'm sure if these develop a trend, my service department would try to upsell me. And even if they don't, I'm aware of such a service, and may end up requesting it during the 60k service anyway. Why not, already dropping a ton of money on the 30k + spark plugs, so what's another ~$100-150 in the long run?

Interestingly enough, I was watching a video on YT the other day about someone putting a new 2021 Touring XT on a dyno (definitely not out of the break in period, yikes), and he compared it to his graph from an Ascent dyno, and they were different.


Happy Subaruing...

Edit - Took these screens of the torque curves and power curves. Red is Ascent.

TLDR - Ascent has more torque but less HP.

501655

501656
 

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I put in e15 yesterday in my xt. So far no performance impact or fuel impact. Getting better mileage right now somehow but only have 40 miles on it. No breaking up or detonation noticed.
 

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I don’t think I’ve ever seen e15 for sale here. It would be tough to remain competitive with Costco. They’re almost always 25 cents cheaper for 87 with credit compared to local cash prices. And in some instances Premium (93) is over $1 difference.

E15 would have to be sold really cheap to make it even considerable and competitive with Costco.
 

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2021 Outback Limited 2.5L - 🍦The Ice Cream Man🍦
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I don’t think I’ve ever seen e15 for sale here. It would be tough to remain competitive with Costco. They’re almost always 25 cents cheaper for 87 with credit compared to local cash prices. And in some instances Premium (93) is over $1 difference.

E15 would have to be sold really cheap to make it even considerable and competitive with Costco.
In my area Kwik Trip and a random smattering of other major brand gas stations offer E15 aka UNL88 and it is usually about 5 cents less per gallon. I used some in an old 2004 Chevy Venture van with no ill effects.

The Gen 6 OBXT can accept it per the owner's manual and turbo engines tend to respond well to higher ethanol content in gasoline so if I had one I would have no issues using it. I cannot speak to getting better or worse fuel economy with it though.
 

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Ethanol has less energy, so therefore less mpg, by volume compared to gasoline. There will be a 4.5% less mpg for e15 compared to straight gasoline.

Ethanol is corrosive to some metals. If a vehicle is designed to run e15 then corrosion should not be a consideration when using this fuel. But, for a purest it may be a component of consideration to use this fuel version.

Costco gas is a good choice. It has a Top-Tier additive rating which adds about 3¢ more per gallon to make this fuel. I am not sure this additive rating helps with a direct injection engine because the fuel is not cleaning the back of the intake valve.
 

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So quick daily drive update on e15. Cannot comment on mpg yet as it's only been 70 miles, but short term fuel trim is normal as is long term fuel trim. No abnormalities with timing or boost as well. In fact, may feel a little more push on the butt dyno. Still boosted to 16.9 on flat out. And to comment on the corrosive aspect of e15, it's only 5 percent more then regular gas, so I'm not to worried about any corrosion, as regular gas would eat up components if they weren't protected
 

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I stick with high quality regular and avoid those who push ethanol additives. I have no intention of ever adding mid or premium.
 

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So I bought a 2020 Subaru Onyx XT. Still have a half tank of gas, but going to a fill up probably this weekend. Just wondering about people thoughts on using premium versus regular unleaded gasoline. What about mid-grade? I know there are benefits to using premium gas.
You do not need premium gas. One easy test is to drive uphill under 75% acceleration or more and if it pings, try the next level octane up. Octane rating only has to do with the compression ratio designed by the manufacturer. There are no other benefits to 91 octane gas.
 

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2020 Onyx
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Octane rating only has to do with the compression ratio designed by the manufacturer. There are no other benefits to 91 octane gas.
True, but it's slightly more complicated:

My 2005 Legacy GT (turbo) had an 8.2:1 compression ratio and 13.5 pounds of boost, premium required (91 minimum)

The 2020 Outback XT has a compression ratio of 10.6:1 and 14.5 psi of boost, 87 octane minimum - this is because of the cooling effect of direct injection among other things.

Instead of just listening by ear for pinging, one can log for knock counts or look for ignition retard. I haven't done that.
 

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2010 Subaru Outback Premium 2.5i w/AWP 6MT
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Instead of just listening by ear for pinging, one can log for knock counts or look for ignition retard. I haven't done that.
I've done it on the Ascent. No problems on 87.
 
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