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2015 Subaru Legacy 3.6R Limited w/ EyeSight
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Sometimes I notice the engine in my 2015 Legacy 3.6R seems peppier than at other times. This morning for example, the engine was a bit more willing; quicker takeoffs, smoother etc. The weather when I leave the house is typically is in upper 50’s. I’ve had the same tank of gas for the last week. My normal routine in the morning is start the car and let it run for 15 seconds before I start out.

I can’t put my finger on any variables that would change the feel of the motor. Any thoughts on the varied performance?
 

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Any increase in so call performance is in your head. Are you wearing the same pair of shoes every time? This can affect how hard you are pushing on the go pedal. Any engine performance increase/decrease due to ambient temperature would be so slight you would need a computer to detect it.
 

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Any increase in so call performance is in your head. Are you wearing the same pair of shoes every time? This can affect how hard you are pushing on the go pedal. Any engine performance increase/decrease due to ambient temperature would be so slight you would need a computer to detect it.
I disagree, as I have also noticed that sometimes the engine is significantly more eager. I think it, for the most part, is related to torque limiting in the tune. For example, if I hammer down from a stop, the car doesn’t take off with the same pep as it does from a roll. That’s been my experience over 61k miles.
 

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I would describe it as engine + CVT more willing to rev up faster. I too see it, saw it with my previous 2.5 as well. But it is very related to the outside temperature. when it is warm up enough, engine warms up faster and seems more agile.
 

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What you are feeling is called "torque converter multiplication" You ought to feel what a SC or turbo does to that TQM. You get in the TQM power band and its like night and day.

The CVT tries to optimize, but sometimes you multiply.

Those with a 2.5 NA will never know.
 

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2016 Outback Premium 2.5 CVT w/EyeSight+SRVD
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What you are feeling is called "torque converter multiplication" You ought to feel what a SC or turbo does to that TQM. You get in the TQM power band and its like night and day.

The CVT tries to optimize, but sometimes you multiply.

Those with a 2.5 NA will never know.
Sorry, but this post makes no sense at all.
 
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The colder the air, the denser it is. Denser air permits the engine to draw in more oxygen, and in turn burn more fuel. More fuel means more power. So in theory you have more power available on a cool morning. In practice, the difference is too subtle to notice across daily temperature swings and the power difference is attributable to other things. Are you running the ac compressor? In the morning it is drawing essentially no power because the car and air are cool. In the afternoon it may be taking a lot more power, especially if the car has been sitting in the sun and the interior is warm.
 

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The OP almost surely has a worn Rendler Spindle. As it moves abnormally on its axially, the ECM senses that as the beginning of a misfire, and cuts power by 20% to prevent engine damage.
 

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All joking aside, I have experienced something like what the OP describes with my 3.6R on a few occasions (pretty rare), and I'm quite certain it's not imagined or ambient temperature related. I'd just call it enhanced throttle response. It's pretty subtle since the throttle response is already quite good.

My old Impreza OBS (2006, EJ25 H4) used to do the same thing, but it was MUCH more noticable and relatively frequent (maybe once a month). That car typically had very laggy throttle response, which I chalked up to it being the first MY using drive-by-wire. Highly irritating, but you learn to compensate.
 

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Sorry, but this post makes no sense at all.
You can see it in torque curves on high HP forced induction motors. It's one reason that many strip junkies prefer automatics.

And the post was mostly as a joke made to continually poke fun at the 2.5 - 3.6 debate.
 

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2015 Outback 3.6R Package 23
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The colder the air, the denser it is. Denser air permits the engine to draw in more oxygen, and in turn burn more fuel. More fuel means more power. So in theory you have more power available on a cool morning. In practice, the difference is too subtle to notice across daily temperature swings and the power difference is attributable to other things. Are you running the ac compressor? In the morning it is drawing essentially no power because the car and air are cool. In the afternoon it may be taking a lot more power, especially if the car has been sitting in the sun and the interior is warm.
Yeah, but...

In the winter, you're burning winter blend fuel that has butane in it. Butane has less energy in it than the other components of gasoline.

In the winter, you have higher wind resistance. PV=nRT. That won't impact 0 to 30 mph but it will certainly impact passing on secondary roads accelerating from 50 mph to 65 mph.

None of us have access to the software for the engine control unit. I'm sure it plays all kinds of games in the name of fuel economy with choice of RPM, how much fuel it is pushing through the injectors, ignition timing, etc. It seems reasonable that depending on sensor inputs, it does things differently so the car has more pop in some conditions than others. I'd bet that has more impact on perceived engine performance than ambient temperature and humidity. The A/C compressor and alternator certainly drain some power but I think it's probably a small fraction of total engine output.
 

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Doesn't the onboard computer compensate for irregularities in the fuel to give you consistent performance throughout the year? Imagine if everyone's car performed differently month by month. This was not even an issue when cars had carburetors and point ignitions.
 

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Doesn't the onboard computer compensate for irregularities in the fuel to give you consistent performance throughout the year? Imagine if everyone's car performed differently month by month. This was not even an issue when cars had carburetors and point ignitions.
No, the onboard computer compensates for irregularities in the fuel to give you the least amount of pollution emissions possible.
 

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Doesn't the onboard computer compensate for irregularities in the fuel to give you consistent performance throughout the year?
No, the onboard computer compensates for irregularities in the fuel to give you the least amount of pollution emissions possible.
Actually, the ECM does actively compensate for the energy content of the fuel (e.g. the energy density of E10 is ~3% less than "pure" gasoline), along with air density, fuel volatility, and other factors. ECM programming strives to balance among several sometimes-competing goals: performance, economy, emissions, driveability, etc.

Like most good engineering, the fuel management systems for modern gasoline engines comprise multitude of design compromises flying in tight formation.
 
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