High octane fuel is generally made for cars that have higher compression ratios. In these cars the lower octane fuel will ignite too early, causing engine knock and performance suffers. The higher octane fuels burn at a higher temperature.
It is a waste of money to use an octane fuel in that is higher than recommended or use high octane when you don’t have an engine knock problem.
Give it time. They always have their hands over any Subaru, and I suspect this one will be no different. I wouldn't be willing to risk my warranty on it, but it's cool nonetheless. Being able turn up the boost would be nice. **** maybe they'll sell some good COBB parts for it
FYI: Subaru's answer to this question has been a consistent "87 octane or better".
You'll find actual emails quoted in these forums. Unless @pilot1226 gets a more specific and contrary answer back from SoA, I'm sticking with the higher octane due to better detergent.
I would consider Costco since the detergent and additive levels are only a little less than Shell's, but I no longer have a membership and don't plan on renewing. So, in the meantime, I'm doing Shell 93.
FYI: Subaru's answer to this question has been a consistent "87 octane or better".
You'll find actual emails quoted in these forums. Unless @pilot1226 gets a more specific and contrary answer back from SoA, I'm sticking with the higher octane due to better detergent.
I would consider Costco since the detergent and additive levels are only a little less than Shell's, but I no longer have a membership and don't plan on renewing. So, in the meantime, I'm doing Shell 93.
Unless something changed, I don’t believe the one off Rt 3 in Clifton requires a membership card. They do require a Visa card though. No cash. $2.67 for 87 today, $2.91 for 93.
Unless something changed, I don’t believe the one off Rt 3 in Clifton requires a membership card. They do require a Visa card though. No cash. $2.67 for 87 today, $2.91 for 93.
Alas, though I visit that state, and bought my car there, I live on Long Island in Suffolk. There's very few near us (Riverhead and White Plains) with gas stations, and the ones (one?) that have pumps require membership for a decent price.
OTOH, I still have to figure out how to rack up my break in miles so I can have some fun, so... :grin:
FYI: Subaru's answer to this question has been a consistent "87 octane or better".
You'll find actual emails quoted in these forums. Unless @pilot1226 gets a more specific and contrary answer back from SoA, I'm sticking with the higher octane due to better detergent.
I would consider Costco since the detergent and additive levels are only a little less than Shell's, but I no longer have a membership and don't plan on renewing. So, in the meantime, I'm doing Shell 93.
I took a look at the Ascent owners manual. It says 87 or better as well. Also warning that using lower octane can potentially cause knock and engine damage. I'm not sure if this vehicle is a lot of people's first turbo vehicle but higher octane is almost always better in a turbo engine.
Thank you for your inquiry about Kirkland Signature Gasoline! If you go to www.costco.com and search: Gasoline, there is an entire website of information about our Gasoline. We believe our fuel quality is second to none.
Our detergent additive package is independently registered with the EPA. The Top Tier program is administered by General Motors, and supported by several other automakers such as Toyota, Honda, BMW, Mercedes-Benz, VW, Fiat Chrysler, Audi and Ford. www.toptiergas.com
In order to qualify and meet the performance standards for TOP TIER, an additive must contain about three times the EPA detergent requirement. Costco's Kirkland Signature Gasoline additive dosage is five times the requirement, which provided the maximum cleaning impact during our engine testing. We additize with the same dosage in both our regular and premium grades, which is 5 times the lowest additive concentration (LAC) allowed by the U.S. Environmental Protection Agency (EPA).
The owner’s manual of my 2009 Subaru Impreza (non-turbo) says the same thing, 87 octane or better. I’d be willing to bet any semi-recently made car supports the same when it was designed for 87. The engine can adjust the timing to support the higher octane gas, the only difference is the price you’re paying at the gas station.
I’ll tell you what—I’ll put 87 octane in my tank, you can put 91 (or 93+) in yours. At 50,000, 100,000, and 150,000 miles we can compare how much we’ve spent in total on engine repairs and gasoline. (Hint: by 150,000 miles you’ll have spent about as much as the cost of a new engine on the price difference of premium fuel. In other words: it’s not worth it)
The owner’s manual of my 2009 Subaru Impreza (non-turbo) says the same thing, 87 octane or better. I’d be willing to bet any semi-recently made car supports the same when it was designed for 87. The engine can adjust the timing to support the higher octane gas, the only difference is the price you’re paying at the gas station.
I’ll tell you what—I’ll put 87 octane in my tank, you can put 91 (or 93+) in yours. At 50,000, 100,000, and 150,000 miles we can compare how much we’ve spent in total on engine repairs and gasoline. (Hint: by 150,000 miles you’ll have spent about as much as the cost of a new engine on the price difference of premium fuel. In other words: it’s not worth it)
To summarize your valid point, if all a person cares about is cost, then use the cheapest gas supported.
I'd be interested to see if there's any difference on a dyno, but I'm not willing to pay for it.
I might use the cheapest Costco gas until COBB comes out with something for the Ascent or Subaru comes out with an explicit update that supports higher octane levels.
I have put 87 in the vehicle so far - just put 2000 miles on the car loaded with kids and bags (although this is probably only like 750 pounds total). I'd probably put 93 in when towing. I imagine the motor will detonate from time to time on 87 when it is hot and heavy and 89, 91 or 93 will help to prevent this and possibly give you a few extra hp.
Thanks for summarizing, but I think my point got lost there. What I was saying is that using anything higher than 87 octane in an engine designed for 87 is a waste of money. It gives you no significant difference in performance, gas mileage, engine longevity, or towing.
If there were a significant difference, Subaru would have put it in the owner’s manual and added it to their performance specs.
I suppose there is a chance that the engine was really designed for 91 octane and for marketing purposes they just aren’t mentioning it. But I think we’ll find out rather quickly if that is the case, the numbers will be significant. I doubt it though — I would’t think Subaru would hamper themselves with the performance specs.
Thanks for summarizing, but I think my point got lost there. What I was saying is that using anything higher than 87 octane in an engine designed for 87 is a waste of money. It gives you no significant difference in performance, gas mileage, engine longevity, or towing.
If there were a significant difference, Subaru would have put it in the owner’s manual and added it to their performance specs.
I suppose there is a chance that the engine was really designed for 91 octane and for marketing purposes they just aren’t mentioning it. But I think we’ll find out rather quickly if that is the case, the numbers will be significant. I doubt it though — I would’t think Subaru would hamper themselves with the performance specs.
https://newsroom.aaa.com/2017/12/dont-fueled-premium-not-always-worth-price/
AAA did an amazingly thorough test across a number of different types of vehicles and, depending on what you consider significant, performance sometimes changed with different octanes in certain conditions (and not always for the better).
Personally, I think Subaru just didn't think it was worth the cost to explicitly engineer, test and verify that using higher octane fuel helped (whether it actually does help or not). We don't even get a driving mode selection that allows the CVT to act like a CVT, which would help with both performance and gas mileage (but that would be another thread).
https://newsroom.aaa.com/2017/12/dont-fueled-premium-not-always-worth-price/
AAA did an amazingly thorough test across a number of different types of vehicles and, depending on what you consider significant, performance sometimes changed with different octanes in certain conditions (and not always for the better).
Personally, I think Subaru just didn't think it was worth the cost to explicitly engineer, test and verify that using higher octane fuel helped (whether it actually does help or not). We don't even get a driving mode selection that allows the CVT to act like a CVT, which would help with both performance and gas mileage (but that would be another thread).
AAA only tested vehicles where the manufacturer explicitly recommended high octane fuels for best performance. In this case, Subaru is recommending a regular octane fuel. AAA’s test results don’t really apply in this case. Though it’s not surprising that in many cases that high octane fuels don’t give a performance difference, and sometimes makes performance worse.
This engine is based off the FXT FA20DIT. The FA20 FXT also states 87 can be used at the expense of performance, gas mileage and possible engine knocking. I can't understand why anyone would spend this much money on their Ascent then cheap out on the gas. It's your vehicle and you can use whatever you want though.
Having owned many turbo cars and even some that say you can use regular unleaded, do your car a favor and just run premium. Turbo vehicles will always run better with higher octane regardless if the ECU can compensate.
I'm willing to try a tank of 87 from Costco and see but ultimately I'd probably still go with a higher octane to be safe. But until there is more data and testing out there, I guess none of us will know.
We can know because the manufacturer told us. Yes the car will run better on 91 but it will be fine on 87 because they tuned the car for both. It's like a flex-fuel vehicle. They program it to run on 87 or on ethanol.
It's not a waste on this car true, but it is 100% incorrect to say that every turbo car will run better, they won't, unless they were specifically programmed for it.
I took a look at the Ascent owners manual. It says 87 or better as well. Also warning that using lower octane can potentially cause knock and engine damage. I'm not sure if this vehicle is a lot of people's first turbo vehicle but higher octane is almost always better in a turbo engine.
Again you're changing what you are saying and agreeing that it's not always better to run higher octane. Plus, I'd bet a good deal of the people here had a wrx at some point in the past.
AAA only tested vehicles where the manufacturer explicitly recommended high octane fuels for best performance. In this case, Subaru is recommending a regular octane fuel. AAA’s test results don’t really apply in this case. Though it’s not surprising that in many cases that high octane fuels don’t give a performance difference, and sometimes makes performance worse.
Again you're changing what you are saying and agreeing that it's not always better to run higher octane. Plus, I'd bet a good deal of the people here had a wrx at some point in the past.
I've never changed my stance on running a higher octane. I said I'd give 87 from Costco a shot due to it being a Top Tier provider with more detergents. You're also cherry picking my comments and making claims on them without having any context as to what I replying to.
Yep, if the figures are correct, when it comes to detergents and related additives, Costco beats all other brands at all octane levels, with the singular (and far more expensive) exception of Shell 93 Octane V-Power. And it's not far behind that one. All of the rest that we've found numbers for trail Shell 93 and all Costco octane levels by quite a bit.
So, I too agree that Costco is quite a nice option, regardless of what octane someone wants to run. Failing that, if someone wants high detergents level, Shell 93 is next, and everything else tested is far away from those two options.
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