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I just took a 1500 mile road trip from Arizona to Iowa in the 500 rwhp supercharged 6 speed gxp and averaged 23 miles per gallon per tank full. My cruise control was set between 74 and 79 depending on the speed limit at the time. I did 16 hours on the second leg of the journey. I have to say these G8's are extremely comfortable. I have to laugh because I get more mpg than the original purchase window sticker, yet I had to pay a gas guzzler tax.
 

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Yep those city/hwy estimates are so far off. My 2006 GTO M6 got 29MPG at 70mph with CAI across country. My bone stock G8 gets 31 at 60mph.
 

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There was one?
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I averaged 23 mpg doing 85 mph through the mountains of Tennessee....... can't imagine the EPA estimates are way off! LOL
 

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I think EPA highway estimates are at 65mph roughly. If your getting 23mpg at 85mph i bet you can get 28+mpg doing 65-70 in the mountains.
 

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You guys are lucky. I'm lucky to see 21 mpg even with DOD on. Mostly highway driving at 60-70 mph.
 

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Mack
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I just averaged about 20mpg on the way NC and back this weekend. I'm on 93 octane, tune, intake and exaust with AFM tuned out though. I don't see how a GXP is getting 23+mpg at 74mph+ but man, more power to ya!
 

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I didn't really notice a change in highway MPG from my GT to GXP. Hard to believe since the GXP is running higher rpms. City you can watch the needle drop though...haha
 

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If you guys are using the computer's avg MPG calculation it is almost always off by at least 2-3 MPG at least in my experience. The only way to figure it out is to use old fasioned math, divide your miles by the amount of gallons used
 

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Mack
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I've been using the fuelly app. Pretty damn cool.
 

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I just averaged about 20mpg on the way NC and back this weekend. I'm on 93 octane, tune, intake and exaust with AFM tuned out though. I don't see how a GXP is getting 23+mpg at 74mph+ but man, more power to ya!
Manual gearing = better mpg, more cubes = less work = better mpg, manual tranny = less weight = better mpg too.

Edit if its an auto still better gearing and more cubes.
 

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Discussion Starter · #14 ·
I manually calculated my mpg during the trip. My tuner pretty much just set the fuel trims given I asked for an very conservative tune. I wanted my car to drive well in all conditions.
 

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MUSCLE Biotch!
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I averaged 23 mpg doing 85 mph through the mountains of Tennessee....... can't imagine the EPA estimates are way off! LOL
I found that I got the best mileage on my trip from the Raliegh area to OKC crusing at 75 mph. 19 hours straight except to eat and fuel up. My average speed was 73mph and 27mpg. AC was on the whole way also. When I drive over 80, I get around 24mpg.
 

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Mack
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Just did a search on Fuelly for fun. Not many folks are getting 27pmg. Or even 24. That's flat out impressive.
 

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I just drove to Albuquerque and back for a one day trade show with 4 of us and a little pooch, trunk & back seat packed to the gills with heavy stuff. So 1000 miles in 3 days and I probably averaged 90 mph, my display gauge said I did 21.3 mpg, which I thought was low but my right foot keeps acting up so I think that's the problem :pimp:

There are some LONG straight and desolate stretches of desert highway on this road trip :secret:
 

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These cars can get great mileage, I'm not complaining about my GT.
 

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On a recent trip I drafted a large bus and kept her AFM on... My DIC said 28 or so but I know it's about 4mpg high 'cause of the bigger injectors. Still, 24mpg isn't bad.
 

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Just did a search on Fuelly for fun. Not many folks are getting 27pmg. Or even 24. That's flat out impressive.
Hey, that's me in the pic!

I'm averaging ~18, but with quite a bit of dense urban city driving mixed in. I'm actually surprised its not worse. I should be able to do 24 highway no problem, maybe more once I get my tune figured out.
 
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