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2011 Forester X Premium AT
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812 Posts
Discussion Starter · #1 ·
Hi,

I have recently ran a tank and a half now of premium (92 octane) gas and the car seems to like it.

I knew this engine has pretty high compression (10.5) but I love being able to fill with regular (87 octane) gas.

Fuel economy seems the same as with regular, throttle response just seems better, power seems slightly higher, nothing drastic, but better.

Anyone try this? Your response?

I will try a tank of regular soon and see if I really did notice a difference. :catfight:
 

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Premium Member
2019 Crosstrek 2018 Forester XT
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15,013 Posts
Total waste of money, really.
 

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2015 Highlander AWD XLE 6AT
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4,255 Posts
The FB25 engine's compression ratio is 10:1 {ref 2012 FSM, page ME(H4DO)-2}.

I've experimented a lot with fuel grades and non-turbo engine performance over the years. The results have varied from engine to engine.

Our '12 Forester is fitted with the FB25 engine. I've found that it seems to run better on 89 AKI while driving around locally at low- to moderate speeds, which includes some steep hills. Specifically, the engine feels smoother and torquier, and I can stay in gear longer before down-shifting.

However, I've found no consistent advantage from higher grade fuel while driving at highway speeds, so 87 AKI it is out on the open road.

HTH,
Jim / crewzer
 

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2019 Crosstrek 2018 Forester XT
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15,013 Posts
CompressionRatio is not the total picture..due to newer technology. My Ninja motorcycle is 12:1 and uses regular gas.
 

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2016 XT Touring CVT
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656 Posts
CompressionRatio is not the total picture..due to newer technology. My Ninja motorcycle is 12:1 and uses regular gas.
However, I bet it's not as much fun in the snow as your Foz!!:woohoo:
 

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2012 Forester 2.5X Mt
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60 Posts
I switched to 93 a little while back. On 87 car pinged occasionally. So I tried the higher octane stuff and the forester definitely seems to run a bit better and peppier and no pinging on the 93. It costs me around ten dollars a month more to run 93.....ken
 

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2019 Crosstrek 2018 Forester XT
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15,013 Posts
I switched to 93 a little while back. On 87 car pinged occasionally. So I tried the higher octane stuff and the forester definitely seems to run a bit better and peppier and no pinging on the 93. It costs me around ten dollars a month more to run 93.....ken
It shouldn't ping ever on 87 IMHO. Others may disagree.
 

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2012 Forester 2.5X Mt
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60 Posts
Yes they are not supposed to ping....but just do a search on google for subaru forester pinging, or for that matter almost any new car, and you will find lots and lots of people complaining about their car pinging. Mine was not too bad and only under certain circumstances did it ping. After trying the 93 and seeing how it runs better, you can of course think I am crazy, but for now I am staying with the 93 because I am hoping to keep this car for a long time and pass it on to my kids so they can learn to drive a stick unlike most people now. My wife's new mazda which also is supposed to only need 87 will sometimes ping. Any new car manual also likely states occasional pinging is okay. I think it's just a nature of new higher compression modern engines that should control any knock thru the knock sensor but don't always.
 

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2011 Forester X Premium AT
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812 Posts
Discussion Starter · #9 ·
Yeah, call me crazy, too, but it does seem to run better on the premium fuel. It is not night and day by any means, just a bit better.

I also have ran regular since I got it, adc, and I thought it ran fine. I was thinking about detergents n cleaning out the fuel system a bit, figured I would run a tank of premium. I used to just run a can of gumout in it every few months on account of the regular gas, but I was told to do that just before you changed oil in the engine because the fuel inj, cleaner would contaminate the oil.

I bet you are right crewzer. I looked it up in the manual a few times early on...but just did a wiki look up just before posting, it said the 10.5. I remembered it was high.....but not that high it seems. When in doubt, RTOM ;)

I will switch back to regular soon to see if it is all in my head....and Ken's. Ha ha
 

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2013 VW CC Sport 6MT
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171 Posts
During the blazing hot Phx summer, running anything less than high quality 89 resulted in noticeably worse performance and economy (1-1.5mpg). Basically, I thought it was easy to hear / feel the difference between 87 and 89 octane when the ambient temps were >90 degrees. I never got the chance to try 91 octane before summer's end.

Now that it's nice out again, 60-80 Fahrenheit, I think 89 and 91 octane offer indistinguishable performance. However, I'm starting to think that the engine might sound happier on 89 in these temps.

While it's still nice out, I want to try:
87 octane again
Pure gas in dif. octanes






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2011 Forester X Premium AT
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812 Posts
Discussion Starter · #11 ·
I too have noticed about 1+ mpg improvement witan premium.
 
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