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Questions regarding Mud Flaps, CAI and Exhaust on 2014 Impreza


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So I drive a 2014 Impreza Sport Premium, not a WRX or STI(I know I should have gotten one of these >.<). The car is automatic however I drive it in manual 100% of the time, yes with the flappy paddles. I've recently throw mudflaps on the car and have noticed roughly 4-8mpg decrease, was curious if anyone has seen this occur? I did do some research and saw some people said there would be very minimal mpg decrease, but i didn't think it would bring me down from 27mpg to 20~23mpg. The other thing I was debating, it's nice and cold here now, would cold weather have effect on a cars mpg? I did notice that due to cold temperature the mpg digital read jumps around a lot and is quite slow and inaccurate at reading when its below 32 degrees outside. The alternative way I've come to guessing how my car is doing is by matching the amount of miles to the amount of gas. For example, usually when the first 3 bars of the tank are gone I should have about 100 miles, sometimes a little less, on the tank, some times a little bit more - but since installing the flaps its been about 70-80 miles on the tank when those bars go away. There's only 6350-6400 miles on the car and I just had my second oil change.

 

Now for the other questions, keep in mind, I am very grateful for all and any answers.

 

To start things off, the car is still under warranty, so I am hesitant to doing any modifications for now, unless someone can explain why my warranty would not be voided.

 

Either way, I am looking into potentially doing a CAI or an exhaust, potentially both after a period of time. Some questions I have, if doing a CAI would I need to tune my car after? I was reading that you would want to but it looked like that was mainly around cars with turbos. My question is, if my car can support a CAI, would it need to be tuned after installation? If so, can someone explain to me why?

 

My other question regarding an exhaust; if I do an exhaust(was currently looking at the Borla Axle Back) would I need to have the CAI to compensate for the output of the exhaust? Some of my friends tell me yes and some no, so I am resorting to you guys for better input.

 

Any sort of guidance on these is much appreciated. I am not a car person, I work with computers, my friends are the car ones - with conflicting information I like to get a wider groups input.

 

Thanks in advance for any input/guidance you guys have for me. :D

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Hello- I have a 2014 Impreza (sedan). I think you'll see a decrease in MPG's this time of year because of different gasoline formulations due to colder weather. In my case (I have the CVT but drive it manually only occasionally) I've been running 32- 33 MPG in mostly longer trip driving (I have an 80 mile round trip commute) but am seeing 30- 31 MPG in the past month. It also takes your engine longer to reach operating temperature in the cold weather (I am noticing the blue temp light is on  longer nowadays). That being said, your MPG drop seems pretty steep. Were there any other changes to your driving/ or the car around the same time?

 

As for tracking gas usage using the gauge, I calculated each bar on the fuel gauge= 1.2 gallons. With my driving, I drop the first bar at around 560 moles after filling up, the second around 90, the third around 130. When it drops 6 bar (at 1/2 tank on the gauge), I usually am down about 7 gallons at that point. I find the MPG's calculated by the ECU to be 2- 4 MPG higher than what I'm getting, but I see those MPG's drop drastically when the car is cold or if taking it for a shorter drive, then gradually climb back to where it was after a longer drive.

 

After what I've read about warranties, I'm a little gun shy about making any mechanical mods to the car at this point. (I did opt for the 100K mile warranty this time). I've started same my oil and filter receipts for warranty purposes in case anything were to happen (never did anything like that with previous new cars). Probably just me being paranoid from reading stories on these forums).

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Hello- I have a 2014 Impreza (sedan). I think you'll see a decrease in MPG's this time of year because of different gasoline formulations due to colder weather. In my case (I have the CVT but drive it manually only occasionally) I've been running 32- 33 MPG in mostly longer trip driving (I have an 80 mile round trip commute) but am seeing 30- 31 MPG in the past month. It also takes your engine longer to reach operating temperature in the cold weather (I am noticing the blue temp light is on  longer nowadays). That being said, your MPG drop seems pretty steep. Were there any other changes to your driving/ or the car around the same time?

 

Yeah I've noticed my blue temp light on longer now as well. I'm driving the hatch version of your car, love the car! The only change that occurred was adding mudflaps. But I wouldn't think mudflaps could create that much drag. I'm almost convinced to take them off, I have also noticed since adding the flaps the car pulls around a lot more from wind(does anyone else experience this??). I mean I do know that I was roughly averaging at 25-27mpg, usually closer to 27mpg. I drive about 45mins to and from work mainly city style driving, occasional roads that hit 45-50mph.

Edited by sturner91
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I found this on another site regarding the MPG decrease with mud flaps. I can't seem to figure out why my mileage would have gone down so much though????    :blink:  :huh:

 

"This is a good question. And the answer is simple, yet complex. As the Mythbusters showed, a tailgate being down actually DECREASES gas mileage, by about 1-2 MPG. The air cycles around and ends up PUSHING on the cab, and creating a partial counter to drag, but the tailgate open allows that air to just rush out, and it will not cycle back into the cab. The concept is similar to a mudflap, they are close enough to the wheel/tire, that most of the time, they won't produce any drag at all, except as measurable on a microscopic level. It won't affect your mileage in any way, especially not that you'd notice. Yeah, you might go from 26.2857394702 MPG to 26.2857394701 MPG, but that's less than a penny more at the pump. You'd have to fill up more than 1,000,000 times to pay even a penny or two more."

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