Weak gas mileage??
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This is a discussion on Weak gas mileage?? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Whats up everyone, Lately I have noticed my fuel economy going downhill, at least I think so. On a full ...

  1. #1
    Registered User STiled's Avatar
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    Weak gas mileage??

    Whats up everyone,

    Lately I have noticed my fuel economy going downhill, at least I think so. On a full tank (filled up 13.5 gallons) I am getting about 200 miles per tank all city driving. My car is a stage 2 tune. APS turboback, APS 65mm intake, prodrive BC, tomei header, ecutek.

    What do you get? Is mine way off? normal?

    Cheers.
    Sleeper stylie...gt30 + tmic

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    well...i have an 04 wrx with a vf30, full exhaust, 565cc injectors with open source tune, 320ish whp and i get 22-24 city and 29+ highway.

    I dont drive like my butts on fire all the time, but I also dont drive like an old man...

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    Moderator Donkey's Avatar
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    You can't just directly compare gas mileage due to the fact that the biggest variable is the driver and their right foot. My recommendation:

    *Clean the MAF sensor
    *Check air filter and clean if required
    *Inflate tires to 36 psi all around
    *Stay out of boost
    *Injector/fuel system cleaner
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    Registered User STiled's Avatar
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    Quote Originally Posted by wudntme View Post
    well...i have an 04 wrx with a vf30, full exhaust, 565cc injectors with open source tune, 320ish whp and i get 22-24 city and 29+ highway.

    I dont drive like my butts on fire all the time, but I also dont drive like an old man...
    What!? thats crazy... you car stock only get 19/25. How does your mpg increase with modifications? You are in the midwest though so I am sure you get better fuel...lucky. We get sold waste water here in the desert, lol.
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    Moderator Donkey's Avatar
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    Quote Originally Posted by STiled View Post
    What!? thats crazy... you car stock only get 19/25. How does your mpg increase with modifications?
    Because modding a car makes the motor more efficient. Not to mention most engine management solutions lean the car out.
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    Registered User msgsti217's Avatar
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    I'm stage 2 protuned with just a Turbo XS TBE and SPT short ram, about half city, half highway and over my last 53 fuel ups, I have averaged 14.9 MPG

    Teh STI (Subaru Impreza) | Fuelly

    I usually cruise at about 80 mph on the freeway, and sometime drive like my butt's on fire as wudntme said Honestly, my goal is to get about 200 miles out of a tank and I usually fill up between 13.5 and 14.5 gallons, depending on when I need to fill up during my commute to school.
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    If you are going to be crazy....it's best to be crazy with no regard for safety at all

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    Registered User STiled's Avatar
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    Quote Originally Posted by Donkey View Post
    Because modding a car makes the motor more efficient. Not to mention most engine management solutions lean the car out.
    Understood. But adding more horsepower--using larger injectors, increasing boost, etc. will require more fuel.
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    Registered User STiled's Avatar
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    Quote Originally Posted by msgsti217 View Post
    I'm stage 2 protuned with just a Turbo XS TBE and SPT short ram, about half city, half highway and over my last 53 fuel ups, I have averaged 14.9 MPG

    Teh STI (Subaru Impreza) | Fuelly

    I usually cruise at about 80 mph on the freeway, and sometime drive like my butt's on fire as wudntme said Honestly, my goal is to get about 200 miles out of a tank and I usually fill up between 13.5 and 14.5 gallons, depending on when I need to fill up during my commute to school.
    I am in the exact same ball park as you.
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    Moderator Donkey's Avatar
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    Quote Originally Posted by STiled View Post
    Understood. But adding more horsepower--using larger injectors, increasing boost, etc. will require more fuel.
    Only if you drive it like you stole it. I have a 18G with 650cc injectors running 20psi. I get better gas mileage than my TD04 with stock injectors. Why? Because of turbo lag and driving my car like an adult. Your right foot dictates your gas mileage. Because I have a much bigger turbo part throttle cruise is spent in vacuum not boost. The engine's air demand hasn't changed with a bigger turbo and injectors.
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    Quote Originally Posted by STiled View Post
    You are in the midwest though so I am sure you get better fuel...lucky. We get sold waste water here in the desert, lol.
    The gas we get in Kansas isn't bad, but i will agree when im in Tucson my car isnt real happy with me... HAHA

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    Registered User Nigel79's Avatar
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    I get 14mpg with my stock 09'sti and 20mpg highway no matter how I drive. I was quite shocked. My '04 GTO got way better gas mileage. This is my first turbo car so I guess I didnt know what to expect but driving conservative I expected more from a 4cyl 2.5L. Don't get me wrong. I drive crazy quite often as well. How can you not?

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    Quote Originally Posted by Nigel79 View Post
    I get 14mpg with my stock 09'sti and 20mpg highway no matter how I drive. I was quite shocked. My '04 GTO got way better gas mileage. This is my first turbo car so I guess I didnt know what to expect but driving conservative I expected more from a 4cyl 2.5L. Don't get me wrong. I drive crazy quite often as well. How can you not?
    I too am a little disappointed with the gas consumption, but not enough to get rid of the car, haha. As far as driving a little crazy, yeah I have had my moments but how can you not give in once in a while when you have a car with decent power/acceleration?
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    Registered User STiled's Avatar
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    Quote Originally Posted by Donkey View Post
    Only if you drive it like you stole it. I have a 18G with 650cc injectors running 20psi. I get better gas mileage than my TD04 with stock injectors. Why? Because of turbo lag and driving my car like an adult. Your right foot dictates your gas mileage. Because I have a much bigger turbo part throttle cruise is spent in vacuum not boost. The engine's air demand hasn't changed with a bigger turbo and injectors.
    Obviously your driving style (right foot weight) is gonna affect the mpg, that a given. But as a rule of thumb, if you want more power it will take more fuel, period. I don't see how one can achieve a large HP increase by just cramming more air in the cylinder, there needs to be more fuel as well?
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    Quote Originally Posted by wudntme View Post
    The gas we get in Kansas isn't bad, but i will agree when im in Tucson my car isnt real happy with me... HAHA
    I hear you, wish we had 93 here. My only option is to add a few gallons of 100 to the 91. Which adds an $15-20 to every fill up, arrg.
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    Moderator Donkey's Avatar
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    Quote Originally Posted by STiled View Post
    Obviously your driving style (right foot weight) is gonna affect the mpg, that a given. But as a rule of thumb, if you want more power it will take more fuel, period. I don't see how one can achieve a large HP increase by just cramming more air in the cylinder, there needs to be more fuel as well?
    You missed it. The VE of the engine has not changed by putting a larger turbo and injectors in. When I am crusing I am not putting out 300+ whp. I am roughly outputting a very efficient 30 whp. Do you see where I am going? I could have 2000cc injectors and I wouldn't use any more gas than 440cc injectors if the airflow is the same. The throttle controls the airflow but a smaller turbo takes less throttle to boost. The difference is the larger turbo is less of a exhaust restriction than the stock one and allows for better throttle response off boost in a normally aspirated manner.
    Last edited by Donkey; 02-09-2010 at 05:33 PM.
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