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I note the requirement is "at least" 87 octane.
Does this mean if you use higher octane ratings that the timing
will advance; theoretically giving you better performance and economy?

Any thoughts?
 

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The timing advance isn't totally based on fuel. It's based on a host of factors and the timing is constantly changing for optimal conditions. But theoretically yes, with a fuel that's more resistant to detonation the car may advance timing a bit more than it did with the lower octane but again, that all depends on many many inputs from the cars sensors.
 

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Twist2Stop said:
It's best to not use higher octane than you need.
Definitely true!

One should always stick to the octane rating that is most optimal for your vehicle. For example, a vehicle that requires 87 or higher only needs 87, there's no need for 89.

And don't use an octane too low, like the Subaru WRX. It's a turbocharged engine, and requires high octane, preferably 93 though 91 can be run.


Heck, one real-world example was when my parents tried running 91 octane when we usually run 87. That long trip we had taken dozens of times, ended up with 1/16th less fuel (and the trip usually has consistent fuel-mileage thanks to my dad's lack of jack-rabbiting)
 

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^
That is true. Using the higher octane fuel can result in MPG changes. However it's not going to do engine damage. The difference in octane simply equates to a higher resistance to detonation. Take e85 for example, it actually has an octane rating of somewhere around 106 which is why a lot of high performance guys use it (with tuning required of course). The higher resistance to detonation won't do damage to you car and may actually allow you to push more timing. But you may suffer mpg costs.
 

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So then my question is what about running 86 octane in the tRek? Here in my state we have 86, 88 and something stupid like 91. 88 is $0.40 more expensive than 86. What will 87 do that 86 won't?
 

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Your lower octane numbers are because of the altitude. In my experience everywhere between I 25 and the Sierra foothills octane numbers are a point or two lower than coastal regions and the plains.
 

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I live a 5K' and I'd run 85 octane, it will be fine. Lowest octane is the fastest burning and packs the biggest punch. My wife has run 85 in her Boxster which calls for 93 octane since '02 and in also in her Lexus that calls for Premium since '06. She drives pretty conservatively and probably never winds the motors up where they need anything more.
 

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Bignick said:
Lowest octane is the fastest burning and packs the biggest punch.
Not quite. Lower octane fuel is more prone to detonation which is bad. Lower octane fuel provides the least potential for making power in an engine. The higher the octane rating the more resistance to detonation, so you can push more pressure and get more power with higher octane fuel without having to worry about detonation. As well as being able to advance timing more aggressively. Detonation is NOT good and usually causes serious engine/piston damage.
There's a reason high HP cars and high revving engines call for premium fuel. Any single detonation event in a car like that can cause serious failure. Driving around tame you might be fine, but open it up once and run it hard and you can be in a world of hurt real fast.
 

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^
That! For this car plain old 87 (ish) is fine and dandy! Sorry to have gone WAY further into that than needed! :-X
 

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Scoobyxv-l said:
I only use 98 octane
Australia uses RON, while the USA uses AKI. Octane ratings vary from region to region.

For example, 98 RON is similar 93-94 AKI.

I've only seen 93 AKI once out of state, because most of California's fuel stations have AKI up to 91 available for most locations. There are, however, rare instances of gasoline/petrol that can be found above 91 AKI (I've seen as high as 100 AKI!).
 

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We can get 106 and sometimes 116 AKI fuel by the race track out here 8) It's NOT cheap though.
 

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I think I've said this in another thread, and it's 99% likely that I am imagining things, but I swear the car preforms slightly better as well as gets slightly better MPG with 91 compared to 85. I'm of course not saying it's shaving seconds off the 0-60 or anything, but it just feels a little peppier. It's probably just placebo since I want to believe it's doing something, but for only $2-$3 more a tank I'll probably keep using 91.
 

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Oh boy! I'll try and be brief. On any turbocharged Sube(since 02 model year) the sensors present to determine timing can take advantage of 100 octane(U.S. rating, so 104 or so in other parts of the world). Now, if Subaru finds it cheaper to adopt this "system"(hardware, software) or parts of, because of economy of scale etc. maybe there could be a difference in that the system on the XV could take advantage of higher octane. ClubCrosstrek getting peppier response and better mpg falls in line with benefits of higher octane especially living in a warmer climate like L.A. Summer time(82-98 degrees) I will top off my tank with some premium(93) in consideration that I will be blasting the A/C and pasting the throttle to the carpet often for more than a second or two. Keep in mind that if you her slight knocking on a consistent basis the odds of you having some crappy gas is high. With most modern cars(last 15 years at least) knock sensors will keep retarding the timing to control knock(detonation). That's why there are some people that say you don't need premium in a WRX, or STi. because the engine won't knock so they think they're fine. I know, stay focused, I'm trying. Higher octane won't hurt XV, driving in hot temps will see biggest benefit. Cold temps of negligible or zero benefit and could take one second longer to start. Last point I promise, it is common for gasoline manufacturers to add the most detergents to the premium fuel and(I'm cheating here) really cheap no-name fuel has minimal detergents.
 

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The benefits of higher octane in relation to higher ambient temperatures probably has a direct correlation to the warmer air that's mixing with the fuel...

Although higher-AKI fuel is more expensive in the summer, I guess it's much more beneficial, especially for those who have leadfoot syndrome such as myself.


Oddly enough, my dad's Honda Ridgeline, which has a minimum AKI of 86, recommends 91 AKI for a heavy-duty use such as towing... I'm guessing the higher temperatures associated with making an engine work harder make the use of higher octane a necessity.


Regarding the "higher octane means more additives", I'm a bit skeptical about that...
 

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Every fuel manufacturer uses different additive packages so that's solely dependent on where you get gas, not necessarily on octane rating. Though some companies do use different additive packages for different octane ratings.

The need for higher octane under higher load is because an engine under heavy load is more prone to detonation.
 
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