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dgoodhue

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I think your city driving has better conditions then EPA's tests. At best I've gotten 21mpg City on my 2012 6MT 2.5i. My average speed is 20mph and I do about 8m a day :lol:. Highway wise I was getting 27-28 until I upped the tire pressure by 10psi, only then I started to see 30-32mpg.

 

Do you adjust your odometer readings to the smaller sized tires? If you don't your actually getting the same MPG as before, it's just your odometer is thinking you traveled more miles :lol:.

 

I'll agree with you though, all of the Japanese cars that I've owned always got higher Highway MPG then EPA, city it's where I'm usually at or below EPA though.

 

Maybe my car is freak, but I can get 34-35mpg on a 2 hour highway trip on my factory sized tires (warmer weather) driving 65-70. My 235 tires drop down 2mpg.

 

I drive about 75% highway or on back roads with no traffic, so I would expect my numbers to be better. I do notice when I do true city driving that the mpg sucks and gets closer to the rate mpg and will go below that on cold snowy days.

 

My 235 or actually a smaller tire height than my factory 205, so the difference is slightly larger. I adjusted my mpg display 5% and now reads what I calculate. (the odometer/speedomter reads slightly faster than my actual speed/distance.)

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My 235 or actually a smaller tire height than my factory 205, so the difference is slightly larger. I adjusted my mpg display 5% and now reads what I calculate. (the odometer/speedomter reads slightly faster than my actual speed/distance.)

 

wouldn't that make the difference smaller because you are dividing a larger mile number than you've actually traveled?

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Maybe, though mine had very high psi in the compression test. I've been running with 93 for a while, because it doesn't knock nearly as much with it, but 93 could be eating my MPG's too.

 

Anyway, +1 for a MT Legacy, I want comfort and fun in same car. Probably wont happen though, so will have to just settle for a WRX when the time comes.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

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wouldn't that make the difference smaller because you are dividing a larger mile number than you've actually traveled?

 

You are right, the calculated difference would be smaller. The difference between the tires is 1% diameter.

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Higher octane don't make the mpgs worse, but it don't make it better either under normal driving. The octane level is only to prevent knocking, but as soon as the spark ignites the fuel it's normal conditions.

 

However a higher octane rating may allow for a different tune including higher compression ratio that is more efficient and may then lower the fuel consumption.

 

Then you will of course count in the lead foot factor when you run the higher octane and don't have to worry as much about knocking.

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Higher octane don't make the mpgs worse, but it don't make it better either under normal driving. The octane level is only to prevent knocking, but as soon as the spark ignites the fuel it's normal conditions.

 

It does when they are using more ethanol to raise the octane rating since ethanol has a lower energy density than gas

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It does when they are using more ethanol to raise the octane rating since ethanol has a lower energy density than gas

 

That wasn't clear from the description - it was only a statement of increasing the octane rating, not changing the blend with another fuel.

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Higher octane don't make the mpgs worse, but it don't make it better either under normal driving. The octane level is only to prevent knocking, but as soon as the spark ignites the fuel it's normal conditions.

 

However a higher octane rating may allow for a different tune including higher compression ratio that is more efficient and may then lower the fuel consumption.

 

Then you will of course count in the lead foot factor when you run the higher octane and don't have to worry as much about knocking.

 

Higher octane fuel has more additives in it to prevent it from auto-igniting during compression, these additives also reduce the speed of the flame front. In layman's terms 93 gas is harder to ignite and it burns slower, which means you need to ignite the mixture earlier in the cycle (BTDC) to get a complete burn, otherwise you will be sending unburnt fuel into your exhaust.

 

This is why 93 gas on a car meant for 87 gas is a waste of time and will yield you lower gas mileage actually (even without ethanol). An 87 gas car can be tuned to use 93 by advancing the ignition timing, this way 93 gas has more time to fully burn up before the cylinder reaches the top dead center.

 

In theory, since 87 gas takes less effort to ignite and burns faster, it should deliver better gas mileage (when tuned for it correctly).

 

Since 2.5i Subaru's are said to use 87 gas, 93 gas in theory (for Subaru's) would bring worse fuel economy, this is why I mentioned the octane when talking to dgoodhue earlier. Reason I say in theory is, Subaru is really aggressive with their NA tunes, I've never seen IAM of 1.0 for any NA Subaru, it's always been much less then 1.0 with 87 gas, aka major knocking. I'm in the middle of re-tuning my 2012 to be more 87 gas friendly, I've pulled 10* of timing from WOT loads and have lost 0HP from the factory timing! I'm also gonna test the gas mileage with much less timing once I'm done with the maps.

 

 

About ethanol, it does have a lower BTU while having a higher octane. Since ethanol burns cooler, it does allow you to run more timing then the equivalent octane 100% gas (good for performance). Since no one really publishes their actual ethanol contents between grades, it's really hard to say. It could very well be that 87 has 1% ethanol while 93 has 10% ethanol. I don't think that would be the case though, since ethanol is highly subsidized and is cheaper, I think 87 would actually have more ethanol then 93, but this is just my theory based on business practices.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

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Since 2.5i Subaru's are said to use 87 gas, 93 gas in theory (for Subaru's) would bring worse fuel economy, this is why I mentioned the octane when talking to dgoodhue earlier. Reason I say in theory is, Subaru is really aggressive with their NA tunes, I've never seen IAM of 1.0 for any NA Subaru, it's always been much less then 1.0 with 87 gas, aka major knocking. I'm in the middle of re-tuning my 2012 to be more 87 gas friendly, I've pulled 10* of timing from WOT loads and have lost 0HP from the factory timing! I'm also gonna test the gas mileage with much less timing once I'm done with the maps.

 

It isn't just Subaru who is doing this with too aggressive part throttle timing. It seems like most manufacturers are using this strategy. One of my other hobbies is riding my bicycle. While riding my bicycle, I often hear audible detonation with low rpm and high loads (i.e. going up hill and accelerating) from various cars. I am surprised at how many new cars are audibly pinging, it hear it on American, Japanese, Korean, and German cars. From econobox to luxury vehicles. Their must be a reason and benefit as to why so many manufacturers are using this strategy.

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My Outback definitely audibly knocked with 87 gas, heck even with 93 (perhaps 100k miles of 87 did enough damage)? I also noticed it being much louder then my 05 LGT, and a 06 2.5i Outback I recently worked on too, I figured price cuts in soundproofing, could have been knock afterall.

 

Some say that they run lots of timing for better fuel economy, but from what I've seen on my GT is that too much timing was actually hurting my economy. This is why I'm now retuning the outback.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

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It isn't just Subaru who is doing this with too aggressive part throttle timing. It seems like most manufacturers are using this strategy. One of my other hobbies is riding my bicycle. While riding my bicycle, I often hear audible detonation with low rpm and high loads (i.e. going up hill and accelerating) from various cars. I am surprised at how many new cars are audibly pinging, it hear it on American, Japanese, Korean, and German cars. From econobox to luxury vehicles. Their must be a reason and benefit as to why so many manufacturers are using this strategy.

 

The low rpm knocks aren't as damaging to the engine as the high rpm ones that you rarely hear over the other noise. The catch is that if you tune the ignition for best torque at low rpms you come close to the knock limit and if the engine control system don't take them into account and tune the ignition timing you will get the knock. But if the ignition timing is downtuned you get worse fuel economy.

 

Then there's probably the matter of people tanking a lower grade gasoline than what the car actually is designed for.

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I think that's what Subaru does with 2.5i's, the knock correction advance (KCA) table does 3-12* of advancement over the already a fairly aggressive base map. They might have even tried to make it a dual octane car, but they didn't do enough to make that be effective.

 

Also about peak torque timing and gas mileage, on my turbo Infiniti peak torque at ~3k rpm was 36* of timing, my best gas mileage was actually at 24* of timing. There was no knock or any signs of engine not being happy at 36*, I just ran out of things to test and anecdotally started removing timing to laugh about it, car went from getting 32mpg to 38mpg.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

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  • 1 month later...
They cut back legacy production, outbacks are still outselling the sedans!

 

yea ever since they stopped calling it a wagon people can't get enough of them. ... they should just sell lowered crossover suv's instead of wagons:spin:

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Maybe later, but it would be an anemic one - like the 1.6 liter DIT found in the Levorg with 170hp.

 

why wouldn't it be the 2.0l that the levorg also gets? i see no point in going turbo charged to have the same hp as the NA 2.5l

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imho, it would actually make sense if subaru kept the 4cyl NA and replaced the 6cyl NA with 4cyl turbo. it would simplify the offerings since 4cyl turbo is already used in wrx/sti/forester. Also with clever tech may be able to improve MPG, at least that's what EcoBoost promised.
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imho, it would actually make sense if subaru kept the 4cyl NA and replaced the 6cyl NA with 4cyl turbo. it would simplify the offerings since 4cyl turbo is already used in wrx/sti/forester. Also with clever tech may be able to improve MPG, at least that's what EcoBoost promised.

That is the most likely move to be made, they may even take the 1.6T and replace the 2.5 and go to all turbocharged layouts. they give the power you want w/ way better gas mileage to a comparable NA (if you can keep your foot out of it)

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why wouldn't it be the 2.0l that the levorg also gets? i see no point in going turbo charged to have the same hp as the NA 2.5l

 

Fuel consumption legislation issues.

 

I suspect that we would see more 3 cylinder engines in the future combined with hybrid tech.

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