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Old 05-13-2009, 09:54 PM   #1
cmiovino
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My '98 OBS has some pinging/ticking before warmed up which is the norm for NA Subarus of that year, especially the EJ22. It's almost totally gone when fully warm, but you can just very faintly hear it if you listen. I was reading around and found that sometimes running higher octane may help reduce the pinging/ticking.

I was thinking about just trying it once, maybe half a tank of mid-grade, and seeing the results. Will this harm my car in any way? Think it will help?
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Old 05-13-2009, 09:56 PM   #2
jeonster
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I doubt higher octane will do any harm
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Old 05-13-2009, 10:19 PM   #3
treksofar
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dude you can run anything in that engine. i find midgrade to be the best/most efficiant due to the high compresion ratio. 87 can cause knocking and 93 just yeilds bad milage.
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Old 05-14-2009, 01:47 AM   #4
jordan s
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my car ticks before its warmed up and i switched to 93 a few months ago and it greatly reduced it. plus the car just runs much stronger/smoother overall and i get better mileage than i did with 87.
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Old 05-14-2009, 02:23 PM   #5
formula91
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The car's advanced timing tables are strung out far beyond even what 93 can do to prevent knocking.

93 will should yield you better gas mileage and less knocking, but you should also calculate the better gas mileage vs cost.

Which honestly, is a pain since gas prices keep changing every week, but whatever.

But they're usually about 10-20 cents apart so you can kind of estimate.

Also some of the tick might be because of the "piston slap." Subaru says this is normal because the pistons are quite big enough when it's cold. Once its warmed up, the pistons expand enough to fit the cylinder better and therefore do not make as much noise. So a lot of it might be normal.
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Old 05-14-2009, 03:29 PM   #6
cmiovino
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Quote:
Originally Posted by formula91 View Post
The car's advanced timing tables are strung out far beyond even what 93 can do to prevent knocking.

93 will should yield you better gas mileage and less knocking, but you should also calculate the better gas mileage vs cost.

Which honestly, is a pain since gas prices keep changing every week, but whatever.

But they're usually about 10-20 cents apart so you can kind of estimate.

Also some of the tick might be because of the "piston slap." Subaru says this is normal because the pistons are quite big enough when it's cold. Once its warmed up, the pistons expand enough to fit the cylinder better and therefore do not make as much noise. So a lot of it might be normal.
It is in fact piston slap... but it just feels like I'm killing it before it gets warmed up all the way, even driving very light on the throttle.
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Old 05-14-2009, 05:48 PM   #7
cmiovino
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Also, I read the manual today and it says 87 is the minimum you should use. Anything above that is ok to use too, just in case anyone was wondering.
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Old 05-14-2009, 07:47 PM   #8
98 OBS for me
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I started useing 93 in my OBS about a month ago and don't see myself going back to 87. I've just found the car runs much smoother and has much smoother power delivery. My milage has remained about the same, but I also have an O2 sensor I still need to install. As for the piston slap, I'd at least give higher octane a try. It's probably not going to cause any harm and you might just like the way your car runs with a higher octane.
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Old 05-14-2009, 08:20 PM   #9
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With 93 or 89 octane, I didn't feel any difference, except in my wallet. 87 for me.
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Old 05-14-2009, 10:39 PM   #10
formula91
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Quote:
Originally Posted by chazly413 View Post
With 93 or 89 octane, I didn't feel any difference, except in my wallet. 87 for me.
Right, it shouldn't be enough gain in torque to actually make a difference, unless some problem makes you ping badly.

It does make a noticeable difference in gas mileage. I used to be 23 mpg on 87, but 89 puts me up to 26. Whether or not this is worth it depends on the gas price I believe. Or rather the difference in gas prices.

Another thing that it does is that it raises your IAM value, but this is linked to the knock that occurs on 87.

One may argue that 93 is better because it is less stressful on your engine. Due to less knock. There is still enough knock to let the IAM value be less than 1 on the 32-bit ECUs. Subaru maintains that this is ok, but we're starting to see many cars starting to fail after 60k, especially the turbo Subarus. I don't think it's as bad on the N/A, but I think we're gonna start seeing more issues soon.

Basically they're giving up reliability for emissions and gas mileage. Those spark timing tables are way strung out. Your engine will have a better time with 93, without knocking. Power? maybe Gas mileage? May not be worth it. But is it better for your engine? As long as the tables are stock, yes.
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Old 05-15-2009, 10:47 AM   #11
Sir-Knight
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maybe someone better at math can correct me with this... and excuse the use of metric, the result should be the same because the mileage is the same between our cars and the gas tank size is the same...

I converted 23 and 26 mpg into liters per 100 km. Using formula91's average numbers will give us a general idea of the difference between 87 and 89. I converted to metric because well.. I'm canadian, and our gas prices are per liters, so it's easier for me to figure out if it's all local to me.

Anyways... around me, 89 AKI is about 7-10 cents more per liter than 87, I'll use the high amount to figure the worst case scenario.

87 @ .90 $/liter (based on the avg price I see today)
60L = 54$
mileage yield is about 587 km at 10.23 L/100 km

89 @ 1.00$/liter
60L = 60$
mileage yield is about 663 km 9.05 L/100 km


The difference in mileage is 76 km per tank.
so I believe to calculate the fuel needed to run that extra 76 km on 87 would be to calculate the amount of fuel needed to run 76/100

so 10.23 L/100 km x .76 = 7.7748 liters

take that amount of fuel needed and multiply that by .90 $

an additional 7$ in fuel is required to run the same distance as running 89.

so 54+7= 61$

so according to the numbers, you will save 1$ (if 89 is 10 cents more than 87 per liter) by running 89.
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