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Old 09-19-2012, 07:05 PM   #1882
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Member#: 314216
Join Date: Mar 2012
Location: ND
2012 2.0i Sport 5MT


Originally Posted by bobdole888

First off, I'm not one of the guys getting 40+ mpg. However, I do feel that gas could have a lot to do with getting better mpg.
For the last 3 tanks of gas, I've been getting ~8% better mpg. This is without any change in driving pattern or weather changes. The only change that I can attribute it to is that my last 3 tanks of gas were regular 87 gas from Rotten Robbie. Previous to this, I was using regular 87 gas from either Unocal 76, or Valero.
The increase in mpg was instantaneous. The mpg meter started showing ~2mpg higher results soon after I got the Rotten Robbie gas.
At some point I'll fill up with Unocal 76 gas again to see if my mpg would drop when that happens. Then I would know for sure that it was the gas that made the difference.
Our impreza is equipped with knock sensor, so if it detects knock, it will automatically retard timing and make the engine less efficient --less mpg.
I'm wondering if the people getting 40+ mpg are putting in 89, 91 gas.
Or maybe they are in states which do not mandate ethanol in gas.
Here in California, ethanol blend is required by law.
For sure ethanol blended gas will result in lower mpg then pure gas.

For the record, my last tank of gas gave me 32.1 mpg(dash), 30.2(calculated). Less than 50% of my drive is freeway.
I'm slightly over the EPA estimate of 30mpg mixed.

I want to try 89, 91 gas at some point also to see if I get any boost in mpg from that.

The other point is tire pressure. I'm running 40 psi to help reduce rolling resistance. I've had problems with running manufacturer's recommended tire pressure in the past. They always seem too low and I end up with tires that wear out on the outer edges, but ok in the center. Hopefully running 40 psi tire pressure will result in more even wear and better mpg.
I've seen in Prius forums that people are running 50 psi over there and are not having any issues with tire wear. They claim to get 0.25mpg for every psi added.
I tried 91, no real improvement, definitely not enough to offset cost.

I also tried higher tire pressure, no improvement and handling was worse. You can do what you wish though with your tires.

I do however get better mpg with real gas and not the crap with 10% ethanol. It doesn't to seem to be 10% better like previous cars, but still 1.5mpg and only cost an extra 0.60 per fill so definitely worth it
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