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Old 09-19-2012, 08:44 PM   #1884
Scooby Newbie
Member#: 315470
Join Date: Apr 2012
Chapter/Region: NESIC
Location: Massachusetts
2012 Impreza LTD
Marine Blue Pearl


Originally Posted by bobdole888 View Post
... I've been getting ~8% better mpg... 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...

Our impreza is equipped with knock sensor, so if it detects knock, it will automatically retard timing and make the engine less efficient... 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...
Wouldn't be a bit surprised if the gas station made a difference. My last car, an Altima, lost 2 mpg when I filled up at Junior's Convenience vs. when I filled up at the New England Farms Mobile. 'Course I had to wait until the next fillup to find out...

Knock sensor - is that peculiar to CA cars? Supposedly I have CA-grade emissions system in my 'preza but first time I've heard of it. Never given much credence to the idea of boosting mpg with octane (didn't work for me after a tank of 89), but maybe...

I'm not as extreme as you, but I have been overinflating for years. I run 36 front/34 rear to get a bit of lift without stiffenning the ride too much. Side note, it took me 2 or 3 weeks to check the tire pressure after buying the car, and when I did I found the dealer had not deflated from the "shipping pressure" (their term) of ~48 psi! No ill effects on the tires I could see.
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