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Old 06-07-2013, 12:50 AM   #4366
stevehnm
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Join Date: Aug 2012
Chapter/Region: SWIC
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2013 Impreza Spt cvt
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Quote:
Originally Posted by G2Spfld View Post
It's more the underpowered smaller motor fuel efficiency type cars affected really. These cars, like other similar cars, rely heavily on maximizing the little HP they have. When the computer is reading the TPS at higher percentages, it has to automatically adjust injectors. When the fuel blends are winter, lower octane, more E85 ( for cars not tuned for E85) we tend to use more petal, or the cruise uses more petal to compensate, thus the higher TPS readings. E85 tuned cars will automatically have much higher injector pulses and widths. It's kinda the same affect the A/C compressor has on power and MPG ( albeit A/C is more of a drag). Now you take a larger engine, and its not using its HP potential most of the time. The A/C has less of an affect on it, and is less noticeable when A/C is on, just as its less noticeable when using winter blend fuel. Before anyone attacks me on this, I have a few cars with Autronic and AEM ECU's. I understand tuning fairly well. This is my take on your point, and why it's not just a Subaru impreza problem.
No, that's a good point, and one that I'm sure Subaru's 2.0 engineers are aware of. Someone made a conscious decision to maximize efficiency (aka fuel economy) at the meager requirements of the EPA highway test, to the detriment of real world performance. The 2.0 does have some oomph at high rpm's - I've never actually seen it not be able to maintain the speed limit on interstate grades, it's just that sometimes on a hill the instantaneous mpg gauge reads under 10mpg (with the CVT that is).

The thing about a larger engine not needing as much reserve and not dropping as much mpg on e.g. the same grade is that it will "slobber" more under no load and is not getting as good mpg as a baseline.
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