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Old 03-09-2011, 02:08 PM   #1
Heavy-Fuel
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Default Modifications vs Gas Milage.

To all the people who have modified their G8, did you see any improvement in fuel economy? I was wondering if you bolt on x-amount in horsepower upgrades, would the car get better gas milage?
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Old 03-09-2011, 02:14 PM   #2
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Its funny as I pondered this on my way to work this morning. Currently I'm seeing an average of 28 miles on the highway and about 22 city. To me thats nice. (Had a TBSS prior too that gave me like 11 city/9 hwy.
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Old 03-09-2011, 02:16 PM   #3
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An intake and exhaust can actually get you better gas mileage. I see and increase of about 2 mpg on the highway with my mods...but it really still all depends on how heavy your right foot is.
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Old 03-09-2011, 02:20 PM   #4
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I'm only getting 16 around the city but that's alot of idling at stoplights (avg mph is 27mph). Highway I can get 27 or 27 at 70 mph.

Intake & tune are going to bump you up a couple mpg, anything after that will likely hurt. Keep in mind, running an aftermarket tune will probably increase the octane reqmt to 91+ so any increase in mileage is cancelled by more expensive gas.
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Old 03-09-2011, 02:33 PM   #5
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Intake, Tune and Exhaust modifications are all designed to increase efficiency and therefore they will increase gas mileage. Any modding beyond these basics usually results in a decrease in gas mileage. My car has seen as high as 29mpg with d.o.d. turned off over the course of a long trip but I usually get closer to 15 or 16 mpg because driving for mpg's isn't nearly as fun as driving for rpm's
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Old 03-09-2011, 02:34 PM   #6
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Without a doubt, most performance improvements also come with MPG increases.

However, if your USING this new power, you'll likely see less MPG.

For the most part though.....CAI, headers and/or cat back, high flow cats, etc should show solid increases in MPG.

The AFM/DoD removal/tune out, can hurt MPG's.

But I noticed on a 2500mi round trip road trip at the end of February, that mileage really decreases after 65mph. I-95 has a 70mph speed limit just south of DC, all the way to Florida. This means people are rolling at 75-80. I set the cruise at 79 both up and back and got 24.7 average for the whole trip. We did minimal driving while down there. Average speed was 67mph when we got home!

My only mod is a Cortex 91 tune. Everything else stock.
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Old 03-09-2011, 03:07 PM   #7
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Modifications make me want to tromp it at a higher percentage of the time.

thus, my gas mileage suffers considerably.
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Old 03-09-2011, 03:47 PM   #8
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I noticed that my 0-60 has improved much more than my mpgs since I've owned the car.
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Old 03-09-2011, 03:52 PM   #9
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Added my CAI, headers, and tune all at once. My MPG has gone from 14.9-15 mpg to 15.5-15.6 mpg. Not a huge increase, but not a decrease either. 99% of my driving is in town.
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Old 03-09-2011, 04:27 PM   #10
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Quote:
Originally Posted by shudog View Post

... an aftermarket tune will probably increase the octane reqmt to 91+ so any increase in mileage is cancelled by more expensive gas.


unfortunately, the GXP has the premium fuel requirement from the factory ...

i find it amusing how GT guys casually make these kinds of comments in this GXP section ...
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Old 03-09-2011, 04:34 PM   #11
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GXP stock I was getting about 26-28 highway under ideal conditions, added headers/high flow cats/ tune and was able to squeeze 30-31 ideal highway driving conditions. Added a supercharger to the mix and Im lucky to see 21 MPG ideal conditions.

So opening up the breathing and tuning absolutely impacted the mileage positively. Once you add in forced induction with higher flow injectors, mileage kind of goes out the window.

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Old 03-09-2011, 05:13 PM   #12
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Back when I had my 04 Chevy Cavi after I modded it with an INJEN intake, headar, hi-flow cat and 2.5 inch exhaust then ported the TB and intake and header it would get 42mpg on the highway with the cruise set at 65mph. The car had the 2.2 ecotec and was a 5spd LS.

Mods DO improve gas mileage till you start useing them.
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Old 03-09-2011, 05:20 PM   #13
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Quote:
Originally Posted by 95_9C1 View Post


unfortunately, the GXP has the premium fuel requirement from the factory ...

i find it amusing how GT guys casually make these kinds of comments in this GXP section ...
I guess I'm guilty with the AFM/DoD comment.

But I never look what "section" I'm in.

I log in and hit [NEW POSTS].

If something piques my interest, I click and comment, contribute, and help where I can.
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Old 03-09-2011, 05:32 PM   #14
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Quote:
Originally Posted by 95_9C1 View Post


unfortunately, the GXP has the premium fuel requirement from the factory ...

i find it amusing how GT guys casually make these kinds of comments in this GXP section ...
Kindof in the same vain as Americans constantly making comments about "soon you'll have to pay $4.50 gallon" to Canadians
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Old 03-09-2011, 06:15 PM   #15
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Quote:
Originally Posted by jhilliard14 View Post
An intake and exhaust can actually get you better gas mileage. I see and increase of about 2 mpg on the highway with my mods...but it really still all depends on how heavy your right foot is.

2nd that, conservative driving is hard though
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Old 03-09-2011, 06:24 PM   #16
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On a V6 all I did was add a CAI and no I really didn't notice any earth shattering MPG improvement. But I did clean my MAF sensor and Throttle Body today, it really needed it after 37K miles. If you have never done it, I highly recommend it. Both needed to be cleaned.
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Old 03-10-2011, 09:39 AM   #17
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Changing the intake does nothing.

A less restrictive exhaust can make an improvement, because it doesn't have a throttle and MAF sensor.
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Old 03-10-2011, 09:42 AM   #18
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Quote:
Originally Posted by mr_didgers View Post
Changing the intake does nothing.

A less restrictive exhaust can make an improvement, because it doesn't have a throttle and MAF sensor.
Then please explain that to my mpg calculations after putting one on...
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Old 03-10-2011, 09:46 AM   #19
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Changing the intake (specifically a high flow filter and smooth intake ducting) would definitely improve mileage.

If something you add gives you horsepower on a dyno, then it has the ability to offer increased efficiency.
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Old 03-10-2011, 09:58 AM   #20
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I have only really checked my highway mileage accurately, to tell snooty tree-huggers that my car can be Sick-Fast and Fuel Efficient as needed. These are my numbers totally stock. I have not had a real opportunity to test after my mods.

HWY 70-73mph on cruise for 2 hours: 24.8 (Verified a couple of times)
HWY 65mph on cruise for 45 minutes: 27.7 (One time test)

I cannot imagine the mods make it worse, only my right foot can do this :-)
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