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Old 06-15-2012, 10:07 PM   #1 (permalink)
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Default Does High Octane gas make a difference?

Filled up at Costco the other day. They were out of regular, so they priced the 91 Octane at the regular price while they were waiting for a truck. I filled up. Now, I am trying to figure out if I am really getting more performance, or if it is all in my head. Some manufacturers recommend only Premium. Some say if you use other than regular, you are wasting your money. Thoughts?
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Old 06-15-2012, 10:42 PM   #2 (permalink)
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This is my take on using premium fuel on a vehicle (non-Subie) designed for regular a few years ago. Sometimes the ethanol-blended supplies I got were so lousy that the premium fuel did make a difference. Quicker off the line, smoother idle and less need for the passing gear. Despite the extra driving enjoyment I received I did not see any mpg improvement. This experiment came to a halt when the fuel prices skyrocketed. Other vehicles I own did not respond differently with premium fuel.
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Old 06-15-2012, 10:53 PM   #3 (permalink)
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If your vehicle recommends (or requires it) I'd say to use it. My former 2003 H6-3.0 Outback recommended 91, when I used lower octane fuel I could tell a major difference. In fact if I used lower than 89 my check engine light would come on until I filled up with higher octane fuel. I was fond of using 92-93 octane fuel when available, my Outback LOVED Shell's 93 gas. Better performance and better fuel economy.

That being said, I see that you have a 2.5L Outback and there is no benefit whatsoever to using fuel higher than 87 octane in it. In fact you will likely get lower performance and decreased fuel economy. Higher octane does not equal higher performance, contrary to the popular misconception. Higher octane fuel does not burn as hot nor has as high an energy content, typically it is used in engines that have cooling systems that cannot keep up with the heat said engines produce. Thus the need for a "cooler burning" fuel, somehow people get the idea that because a high performance engine uses high octane fuel that means high octane fuel = high performance.
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Old 06-15-2012, 11:21 PM   #4 (permalink)
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never noticed a difference ever. i've tried it here and there for kicks, while towing enormous loads in my subaru's, etc. nothing.

my current 2002 H6 and 2003 H6 (which i think recommend higher grades) don't respond any differently. i put the lowest cheapest name brand gas in there and call it good - runs great and no gas mileage difference, which suggests a fairly high correlation to gas mileage given the long distance highway driving i do.
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Old 06-16-2012, 01:21 AM   #5 (permalink)
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I have run 87, 89, 91, 92, 93 in Kaylee (calls for 87 minimum) and have found no difference in MPG or performance. So I fill with 87 from a top tier station with decent customer volume. Stale gas is bad.
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Old 06-16-2012, 01:37 AM   #6 (permalink)
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Higher octane fuel is "more" stable than lower octane fuel. Performance engines have more extreme temps and compression than super low tech engines like the old non turbo 2.5 designed to run on low octane fuels.

So a properly running 2.5 non turbo subaru could care less what your running in it. Running low octane less stable fuel in high performance engines can and usually does result in the less stable fuel ignighting at the wrong time causing damage or having the engine system dial back timing and power to avoid engine damage. The old 2.5 runs fine on the low octane fuel so zero reason to buy the more stable higher octane fuel. As for power? All gasoline blends contain the same stored energy per volume of fuel. Octane rating plays no role in power.
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Old 06-16-2012, 02:27 AM   #7 (permalink)
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I think this puts it in the fairest perspective:
In theory, even fairly basic engines could have engine management that allows you to squeeze a bit more usable power from your fuel, but not a whole lot and its certainly not being done by the factory.
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Old 06-16-2012, 08:53 AM   #8 (permalink)
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Quote:
Originally Posted by Euchre View Post
I think this puts it in the fairest perspective:
5th Gear - High Octane Fuels - YouTube
In theory, even fairly basic engines could have engine management that allows you to squeeze a bit more usable power from your fuel, but not a whole lot and its certainly not being done by the factory.
Well that tells the story quite well. Regular fuel save me about .25 cents a gallon X about 50 gallons a month. Or $12,50 X 12 months, for about $150 a year savings. Regular it is. BTW, I had no idea you could get 98 Octane in the UK.

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Old 06-16-2012, 09:10 AM   #9 (permalink)
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Quote:
Originally Posted by Zioncanyon View Post
Well that tells the story quite well. Regular fuel save me about .25 cents a gallon X about 50 gallons a month. Or $12,50 X 12 months, for about $150 a year savings. Regular it is. BTW, I had no idea you could get 98 Octane in the UK.

I believe UK and other countries use a different method of determining Octane than the US. So their 98 Octane fuel isn't much different than our 93 Octane.

I know wikipedia should be taken at face value, but this arcticle sums it up.
Octane rating - Wikipedia, the free encyclopedia

As everyone else has said, a properly running engine that is not designed to run on higher octane fuel will see no benefit from it, and possibly will have negative effects. If you have another problem that is causing knocking or another detonation problem higher octane could mask it with it's inherent properties.
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Old 06-16-2012, 09:55 AM   #10 (permalink)
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In the H6, yes. In the H4, probably not.

I have noticed the same things as Ignatius when I've put 87 or 89 in my LL Bean. It acts gutless and fuel economy suffers. I figure that 93 is only around 20 cents more, so $3.00 per fillup tops. I can afford that, so I might as well give the car what Subaru recommends.
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