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87 or 91+ octane?

COJeeper

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Though mine is an EcoDiesel, my wife Subaru Forester takes 87 octane, but I like to throw in the 91 plus octane fuels every two to three fill ups because I find the higher octane fuels tend to help burn off a lot of the gunk in the engine.

There's a buc-ee's one city over from us, and I go there once a month and load her car up with the ethanol-free blue pump, it comes out to like 93 octane I believe, but with no corn in it. Amazing for the engine, sucks for the wallet, but it's still cheaper on average than diesel fuel around here. Her car doesn't seem to respond too much differently to it, but last time we took it to the dealership for a warranty repair on the engine, they said that the engine looks meticulously maintained. And even asked me what I have been putting in it. I thought they were being smart, but I've also heard that the higher octane helps burn off a lot of the gunk that the additives clean off, just add a more efficient level.

Better burn; cleaner engine, less corn; cleaner engine, cleaner engine; longer engine life, cleaner engine; less serious maintenance, less serious maintenance; lower maintenance cost.

You could dump any number of additives in there and probably get similar results, but a lot of the additives I've read on a older engineering forum years ago, basically just add a bunch of lubricants which the gasoline already has in it, and increases the octane so it gets a better burn. But you're adding like 16 oz to 18 to 23 gallons of gas depending what make and model you have. It's not going to make a huge difference, not quite like adding 18 to 23 gallons higher octane fuel.

If you want it save on cost, at minimum I would do every third or fourth tank with higher octane fuel. Just my personal preference, I'm no chemical engineer.

EDIT: I should probably note the Subaru Forester she has is a 2.5L non-turbo engine
Buc-ees! mmmmm jerky.

I was in GA for work and stopped in Buc-ees, man, what a breakfast I had! Two burritos and a sandwich and giant freaking soda! Then I brought back to the office a bunch of beef jerky to share. Good stuff!!!!
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Buc-ees! mmmmm jerky.

I was in GA for work and stopped in Buc-ees, man, what a breakfast I had! Two burritos and a sandwich and giant freaking soda! Then I brought back to the office a bunch of beef jerky to share. Good stuff!!!!
Whenever I got a long drive ahead of me, it's definitely my first stop on my way out the house. I like their root beer. Not sure where they source it from, but they're in-house root beer is legit!!
 

jmr

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The 3.6L PUG version has static compression ratio of 11.3:1 which is more the 2.0L at 10:1.
The 2.0L makes 24 psi of boost so that increases the combustion pressure even more than the 3.6.
Which is why the factory suggests 91 octane for the 2.0L. If knock is detected the ignition timing is backed down and the turbo will not make as much boost.

On a side note a SRT tune bumped the 2.0L to 340 hp and 369 lb-ft of torque .
 

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Whenever I got a long drive ahead of me, it's definitely my first stop on my way out the house. I like their root beer. Not sure where they source it from, but they're in-house root beer is legit!!
ooooo Thanks for sharing! I love root beer! I'll have to check that out the next time I'm near one.
 

Yawnie'sPapa

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Static compression doesn't count as much as it used to. The cams, valve timing, valve lift and other factors determine dynamic compression and quick-burn chambers lessen the chances of detonation. There's better heat control, better mixture control, and the EGR to quiet things down.

I was asking a similar octane question in the 4xe forums and - then was promptly shown the "book" - the 4xe supplement........
Same 2.0 turbo engine, but with the 4xe it has help and isn't tasked with taking on so much load. So the 4xe supplement says with that setup, 87 octane.
The non-4xe is doing the work all by itself, the HP and torque ratings are pure 2.0, hills, high combustion pressures and temperatures that the 4xe won't see due to the electric assist.

So, I'm settled on 87 for the 2.0 in the 4xe, 91 on the non-4xe and 87 top tier in my JT's 3.6
 

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Static compression doesn't count as much as it used to. The cams, valve timing, valve lift and other factors determine dynamic compression and quick-burn chambers lessen the chances of detonation. There's better heat control, better mixture control, and the EGR to quiet things down.

I was asking a similar octane question in the 4xe forums and - then was promptly shown the "book" - the 4xe supplement........
Same 2.0 turbo engine, but with the 4xe it has help and isn't tasked with taking on so much load. So the 4xe supplement says with that setup, 87 octane.
The non-4xe is doing the work all by itself, the HP and torque ratings are pure 2.0, hills, high combustion pressures and temperatures that the 4xe won't see due to the electric assist.

So, I'm settled on 87 for the 2.0 in the 4xe, 91 on the non-4xe and 87 top tier in my JT's 3.6
Reminds me that I wanted to see if I can monitor engine timing advance and boost pressure while driving around and see if it changes noticeably between 87 and 91.
 

Yawnie'sPapa

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Reminds me that I wanted to see if I can monitor engine timing advance and boost pressure while driving around and see if it changes noticeably between 87 and 91.
I've monitored timing on my 3.6 with jscan but it changes so often, so much, and a wide range, not sure how you'd figure a baseline.
I'd not expect a real noticeable change, really. Doesn't take much timing changes even in older engines to avoid detonation. And these can control it in multiple ways.
It might be fun, or interesting, anyway. I'd like to see if you do, what results you come up with.
 

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Our 2.0T is noticeably more zippy with 93 than 87.
 

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Our 2.0T is noticeably more zippy with 93 than 87.
I wish someone had access to the means to qualitatively test this on a dyno or a track. I'd love to know how much more power is available with a higher octane fuel. That way I could decide if it was worth paying extra at the pump.
 

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jjvincent

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I wish someone had the money to the means to qualitatively test this on a dyno or a track. I'd love to know how much more power is available with a higher octane fuel. That way I could decide if it was worth paying extra at the pump.
Fixed if for ya.

Evereyone has access to a chassis dyno. It would be easy. Pump the tank, put in 91. Run it and get the corrected numbers. Pump the tank, put in 87 and repeat. Just do a search and you'll find one in the area. Like anything else, it costs money and that's what stops people from doing it.

Eveeryone has access to a drag strip. Find a local one that has a test and tune night. Do a few runs with 91. Pump the tank and repeat with 87. Make sure that the weather has not changed much as that will change times. I used to run a NHRA Super Comp Dragster, so I know that weather can make a difference. Like above, that takes money.
 

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I've run 89 in both my 2.0Ts.
 

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We have run regular 87 almost every fill up prior to the last few fills. I used the Jeep (its the wifes) a couple weeks ago. I honestly could hear very light detonation with part throttle load. I have since done two complete fills with super 93. Not only is that detonation gone, the Jeep honestly feels much more lively. Even my wife noticed it. I know seat of the pants is hard to take as truth, the detonation being gone is all I need to know to keep up using 93. $300 a year is all it costs for us. Honestly a no brainer!
 

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I’ve treated mine as I have with any turbo or supercharged vehicles I’ve ever had. I’ve ran 93 since day one. On average it only cost me $3-$5 more a tank to use 93 instead of 87.
 

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Fixed if for ya.

Evereyone has access to a chassis dyno. It would be easy. Pump the tank, put in 91. Run it and get the corrected numbers. Pump the tank, put in 87 and repeat. Just do a search and you'll find one in the area. Like anything else, it costs money and that's what stops people from doing it.

Eveeryone has access to a drag strip. Find a local one that has a test and tune night. Do a few runs with 91. Pump the tank and repeat with 87. Make sure that the weather has not changed much as that will change times. I used to run a NHRA Super Comp Dragster, so I know that weather can make a difference. Like above, that takes money.
unlike your car we have knock sensors.
You can just datalog and look at the timing.

anything above 87 in the 2.0 is throwing money in the toilet

edit:only data I’ve seen is from the 2.0 in the 4xe, it could possibly be tuned differently than the non 4xe
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