Here is a response from SOA to someone who wrote them and posted the response on SubaruOutback.org.
Thank you for taking the time to contact us. We hope that you have been enjoying your 2006 Outback 3.0R Wagon.
The 3.0-liter H6 engine is designed to operate using unleaded gasoline with an octane rating of 91 AKI or higher. Regular unleaded gasoline with an octane rating of 87 AKI or higher may be used. This is not just for emergency situations. You can use regular unleaded fuel in your vehicle on a regular basis. However, for optimum engine performance and driveability, it is recommended that you use 91 AKI or higher grade unleaded gasoline.
You may experience reduced output, poor accelerator response, and reduced fuel economy when using gasoline with an octane rating lower than 91 AKI, depending on your driving habits and conditions.
If you experience any of those conditions while using a lower octane rated fuel, you may want to return to using 91 AKI octane rated fuel as soon as possible. Additionally, if your vehicle knocks heavily or persistently, or if you are driving with heavy loads such as when towing a trailer, the use of 91 AKI or higher grade unleaded gasoline is required.
Thank you for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again.
Best wishes,
John J. Mergen
Subaru of America, Inc.
Customer/Dealer Services Department
Oil Recommendation :2020 Subaru Legacy 2.4 turbo
- Thread starter R18A1
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My Subaru Ascent has that same motor.
I use Supertech synthetic 5w30 and change it every 6000 miles.
wemay
Site Donor 2023
Originally Posted by jbutch
Originally Posted by wemay
My wife's Hyundai 2.0T runs no better on 93 than on 87. Even though I fill it up mostly with 93, my better (smarter) half uses 87 and I can never tell by feel, sounds or mpg.
I'm now running 87-89 in the Passat 2.0T Budack Cycle. Same thing, no difference whatsoever.
Originally Posted by wemay
Yes, both are 87. The VW manual says "performance "May" be enhanced with higher Premium", but when I did, I never noticed a thing (10,000 miles).
My experience is getting old now, but I worked on a component for a knock detection system for a major US OEM back in the '90s and it was capable of making adjustments on the fly for octane level.
The engine guys told us the sweet spot for them was to have the engine knocking at a low level that was not possible for the driver to notice...that gave them the best power/mileage combo. The system my company developed strove to give our customer the ability to ride that edge (if they wanted to) and the filtering and windowing that was needed to reject vibrations that weren't due to knock was all pretty impressive. This was mass market stuff, not just intended for high end vehicles but across their entire line in a standard ECM.
Things could have changed a lot by now and every engine and engine control scheme is different, but a modern knock control system integrated into an overall engine control scheme should give most vehicles the capability to get at least a little benefit from higher octane gas. Could be so little that it's nearly impossible to notice...
Back when I was in college the term I remember was "incipient knock". Almost, right up to, but not quite.
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